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CHEMISTRY (537 journals)                  1 2 3 4 5 6 | Last

2D Materials     Hybrid Journal   (Followers: 3)
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 31)
ACS Catalysis     Full-text available via subscription   (Followers: 24)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 13)
ACS Combinatorial Science     Full-text available via subscription   (Followers: 8)
ACS Macro Letters     Full-text available via subscription   (Followers: 17)
ACS Medicinal Chemistry Letters     Full-text available via subscription   (Followers: 25)
ACS Nano     Full-text available via subscription   (Followers: 270)
ACS Photonics     Full-text available via subscription   (Followers: 2)
ACS Synthetic Biology     Full-text available via subscription   (Followers: 8)
Acta Chemica Iasi     Open Access  
Acta Chimica Sinica     Full-text available via subscription  
Acta Chimica Slovaca     Open Access   (Followers: 5)
Acta Chromatographica     Full-text available via subscription   (Followers: 10)
Acta Facultatis Medicae Naissensis     Open Access   (Followers: 1)
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 4)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 3)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 4)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 8)
Advanced Functional Materials     Hybrid Journal   (Followers: 34)
Advances in Chemical Engineering and Science     Open Access   (Followers: 21)
Advances in Chemical Science     Open Access   (Followers: 8)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 13)
Advances in Drug Research     Full-text available via subscription   (Followers: 17)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 7)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 12)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 13)
Advances in Nanoparticles     Open Access   (Followers: 11)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Polymer Science     Hybrid Journal   (Followers: 38)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 10)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 4)
African Journal of Chemical Education     Open Access   (Followers: 1)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 4)
Afrique Science : Revue Internationale des Sciences et Technologie     Open Access  
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Alchemy     Open Access   (Followers: 3)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 4)
AMB Express     Open Access   (Followers: 1)
American Journal of Applied Sciences     Open Access   (Followers: 28)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 165)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 11)
American Journal of Chemistry     Open Access   (Followers: 17)
American Journal of Plant Physiology     Open Access   (Followers: 9)
American Mineralogist     Full-text available via subscription   (Followers: 2)
Analyst     Full-text available via subscription   (Followers: 35)
Angewandte Chemie     Hybrid Journal   (Followers: 16)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 213)
Annales UMCS, Chemia     Open Access   (Followers: 2)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 1)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 2)
Annual Reports Section B (Organic Chemistry)     Full-text available via subscription   (Followers: 4)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 10)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 12)
Anti-Infective Agents     Hybrid Journal   (Followers: 1)
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 4)
Applied Spectroscopy     Full-text available via subscription   (Followers: 12)
Applied Surface Science     Hybrid Journal   (Followers: 14)
Arabian Journal of Chemistry     Full-text available via subscription   (Followers: 6)
ARKIVOC     Open Access   (Followers: 1)
Asian Journal of Biochemistry     Open Access   (Followers: 1)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 4)
Autophagy     Full-text available via subscription   (Followers: 1)
Avances en Quimica     Open Access   (Followers: 1)
Biochemical Pharmacology     Hybrid Journal   (Followers: 6)
Biochemistry     Full-text available via subscription   (Followers: 204)
Biochemistry Insights     Open Access   (Followers: 4)
Biochemistry Research International     Open Access   (Followers: 4)
BioChip Journal     Hybrid Journal   (Followers: 1)
Bioinorganic Chemistry and Applications     Open Access   (Followers: 4)
Biointerface Research in Applied Chemistry     Open Access   (Followers: 1)
Biointerphases     Open Access  
Biomacromolecules     Full-text available via subscription   (Followers: 17)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 5)
Biomedical Chromatography     Hybrid Journal   (Followers: 7)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 2)
BioNanoScience     Partially Free   (Followers: 4)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 30)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 24)
Bioorganic Chemistry     Hybrid Journal   (Followers: 5)
Biopolymers     Hybrid Journal   (Followers: 13)
Biosensors     Open Access   (Followers: 3)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 1)
Bulletin of the Chemical Society of Japan     Full-text available via subscription   (Followers: 12)
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 3)
Canadian Journal of Chemistry     Full-text available via subscription   (Followers: 6)
Canadian Mineralogist     Full-text available via subscription   (Followers: 1)
Carbohydrate Research     Hybrid Journal   (Followers: 10)
Carbon     Hybrid Journal   (Followers: 37)
Catalysis for Sustainable Energy     Open Access   (Followers: 2)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 4)
Catalysis Science and Technology     Free   (Followers: 4)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 4)
Catalysts     Open Access   (Followers: 6)
Cellulose     Hybrid Journal   (Followers: 4)
Central European Journal of Chemistry     Hybrid Journal   (Followers: 5)

        1 2 3 4 5 6 | Last

Journal Cover Advanced Functional Materials
   Journal TOC RSS feeds Export to Zotero [36 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1616-301X - ISSN (Online) 1616-3028
     Published by John Wiley and Sons Homepage  [1604 journals]   [SJR: 4.862]   [H-I: 136]
  • Masthead: (Adv. Funct. Mater. 39/2014)
    • Pages: n/a - n/a
      PubDate: 2014-10-15T12:40:37.213668-05:
      DOI: 10.1002/adfm.201470259
  • Materials Meets Concepts in Molecule‐based Electronics
    • Authors: Frank Ortmann; K. Sebastian Radke, Alrun Günther, Daniel Kasemann, Karl Leo, Gianaurelio Cuniberti
      Pages: n/a - n/a
      Abstract: In this contribution, molecular materials are highlighted as an important topic in the diverse field of condensed matter physics, with focus on their particular electronic and transport properties. A better understanding of their performance in various applications and devices demands for an extension of basic theoretical approaches to describe charge transport in molecular materials, including the accurate description of electron–phonon coupling. Starting with the simplest case of a molecular junction and moving on to larger aggregates of bulk organic semiconductors, charge‐transport regimes from ballistic motion to incoherent hopping, which are frequently encountered in molecular systems under respective conditions, are discussed. Transport features of specific materials are described through ab initio material parameters whose determination is addressed. Molecular semiconductors are intriguing materials with applications in flexible electronics due to their potential low‐cost processing ability and chemical tunability. In addition, they are utile in fundamental studies of decoherence effects in single‐molecular junctions. Concepts of transport modeling for such systems are presented in this Feature Article, highlighting the unique transport properties of organic and molecular semiconductors.
      PubDate: 2014-10-14T11:32:31.870027-05:
      DOI: 10.1002/adfm.201402334
  • Effects of Delocalized Charge Carriers in Organic Solar Cells: Predicting
           Nanoscale Device Performance from Morphology
    • Authors: Adam G. Gagorik; Jacob W. Mohin, Tomasz Kowalewski, Geoffrey R. Hutchison
      Pages: n/a - n/a
      Abstract: Monte Carlo simulations of charge transport in organic solar cells are performed for ideal and isotropic bulk heterojunction morphologies while altering the delocalization length of charge carriers. Previous device simulations have either treated carriers as point charges or with a highly delocalized mean‐field treatment. This new model of charge delocalization leads to weakening of Coulomb interactions and more realistic predicted current and fill factors at moderate delocalization, relative to point charges. It is found that charge delocalization leads to significantly increased likelihood of escaping interface traps. In isotopic two‐phase morphologies, increasing the domain sizes leads to slight decreases in predicted device efficiencies. It was previously shown that tortuous pathways in systems with small domain sizes can decrease device performance in thin film systems. However, the diminishing effects of Coulomb interactions with delocalization and efficient separations of excitons by small domains make morphological effects less pronounced. The importance of delocalization, which has largely been ignored in past simulations, as a parameter to consider and optimize when choosing materials for organic solar cells is emphasized. The effects of charge delocalization on device efficiency is probed using mesoscale Monte Carlo simulations of charge transport in idealized and isotropic two‐phase morphologies. Interfacial charge trapping is drastically reduced when Coulomb interactions are weakened through moderate delocalization (1.0–2.0 nm). Morphological differences become less dominant as charges delocalize.
      PubDate: 2014-10-14T11:32:19.097764-05:
      DOI: 10.1002/adfm.201402332
  • Temperature‐Dependent Electrical Transport in Polymer‐Sorted
           Semiconducting Carbon Nanotube Networks
    • Authors: Jia Gao; Yueh‐Lin (Lynn) Loo
      Pages: n/a - n/a
      Abstract: The temperature dependence of the electrical characteristics of field‐effect transistors (FETs) based on polymer‐sorted, large‐diameter semiconducting carbon nanotube networks is investigated. The temperature dependences of both the carrier mobility and the source‐drain current in the range of 78 K to 293 K indicate thermally activated, but non‐Arrhenius, charge transport. The hysteresis in the transfer characteristics of FETs shows a simultaneous reduction with decreasing temperature. The hysteresis appears to stem from screening of charges that are transferred from the carbon nanotubes to traps at the surface of the gate dielectric. The temperature dependence of sheet resistance of the carbon nanotube networks, extracted from FET characteristics at constant carrier concentration, specifies fluctuation‐induced tunneling as the mechanism responsible for charge transport, with an activation energy that is dependent on film thickness. Our study indicates inter‐tube tunneling to be the bottleneck and implicates the role of the polymer coating in influencing charge transport in polymer‐sorted carbon nanotube networks. The temperature‐dependent electrical transport in polymer‐sorted semiconducting carbon nanotube networks is elucidated in this work. The source‐drain current and mobility in polymer‐sorted carbon nanotube network‐based field‐effect transistors decrease with decreasing temperature attributable to fluctuation‐induced tunneling. The barrier for charge transport inversely correlates with carbon nanotube network thickness, for the probability to sample conductive pathways with fewer inter‐tube junctions increases with increasing thickness.
      PubDate: 2014-10-14T11:31:33.854493-05:
      DOI: 10.1002/adfm.201402407
  • Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin
           Films of BiFe0.5Mn0.5O3
    • Authors: Eun‐Mi Choi; Thomas Fix, Ahmed Kursumovic, Christy J. Kinane, Darío Arena, Suman‐Lata Sahonta, Zhenxing Bi, Jie Xiong, Li Yan, Jun‐Sik Lee, Haiyan Wang, Sean Langridge, Yong‐Min Kim, Albina Y. Borisevich, Ian MacLaren, Quentin M. Ramasse, Mark G. Blamire, Quanxi Jia, Judith L. MacManus‐Driscoll
      Pages: n/a - n/a
      Abstract: Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X‐ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. A new window for designing multiferroic materials through epitaxial strain control: For the first time, coexistent ferrimagnetism and ferroelectricity is demonstrated at RT in BiFe0.5Mn0.5O3 (BFMO) by strain engineering. The most highly strained and crystalline films have a ferrimagnetic transition temperature of ∼600 K, which is 500 K higher than bulk BMO and a piezoresponse amplitude of 45 pm/V.
      PubDate: 2014-10-14T11:31:03.495917-05:
      DOI: 10.1002/adfm.201401464
  • From Chiral Islands to Smectic Layers: A Computational Journey Across
           Sexithiophene Morphologies on C60
    • Authors: Gabriele D'Avino; Luca Muccioli, Claudio Zannoni
      Pages: n/a - n/a
      Abstract: A theoretical investigation of the molecular organization at a sexithiophene (T6)‐C60 fullerene planar heterojunction, based on atomistic molecular dynamics, is presented, in which the effect of two different sample preparation processes on the resulting interface morphology is explored. First, the landing of T6 on C60(001) substrate is considered, which leads to crystalline layers of standing and tilted molecules, in accordance with experiments. The observation and the quantitative characterization of the nucleation and growth provide detailed insights on this out‐of‐equilibrium process, including the establishment of an epitaxial relationship between the substrate and the interfacial T6 layer, and the spontaneous formation of defective islands, characterized by chiral edges, during the growth of the second and third layers. It is then shown that molecular orientations can be radically changed upon annealing at 600 K, at which T6 forms a smectic phase with planar alignment, whose layers are perpendicular to the interface. The interfacial T6 morphologies are then analyzed in detail at room temperature and compared to the known bulk polymorphs. The morphology of sexithiophene thin films deposited over a C60 fullerene crystalline slab is investigated with an atomistic molecular dynamics technique. Simulations show that the nucleation and growth of vapor‐deposited sexithiophene leads to the formation of weakly correlated crystalline layers of standing molecules, while the orientation of sexithiophene molecules can be radically changed to planar upon thermal annealing.
      PubDate: 2014-10-14T11:30:58.115475-05:
      DOI: 10.1002/adfm.201402609
  • Strategy for Enhancing the Dielectric Constant of Organic Semiconductors
           Without Sacrificing Charge Carrier Mobility and Solubility
    • Authors: Solmaz Torabi; Fatemeh Jahani, Ineke Van Severen, Catherine Kanimozhi, Satish Patil, Remco W. A. Havenith, Ryan C. Chiechi, Laurence Lutsen, Dirk J. M. Vanderzande, Thomas J. Cleij, Jan C. Hummelen, L. Jan Anton Koster
      Pages: n/a - n/a
      Abstract: Current organic semiconductors for organic photovoltaics (OPV) have relative dielectric constants (relative permittivities, ε r) in the range of 2–4. As a consequence, Coulombically bound electron‐hole pairs (excitons) are produced upon absorption of light, giving rise to limited power conversion efficiencies. We introduce a strategy to enhance ε r of well‐known donors and acceptors without breaking conjugation, degrading charge carrier mobility or altering the transport gap. The ability of ethylene glycol (EG) repeating units to rapidly reorient their dipoles with the charge redistributions in the environment was proven via density functional theory (DFT) calculations. Fullerene derivatives functionalized with triethylene glycol side chains were studied for the enhancement of ε r together with poly(p‐phenylene vinylene) and diketopyrrolopyrrole based polymers functionalized with similar side chains. The polymers showed a doubling of ε r with respect to their reference polymers in identical backbone. Fullerene derivatives presented enhancements up to 6 compared with phenyl‐C61‐butyric acid methyl ester (PCBM) as the reference. Importantly, the applied modifications did not affect the mobility of electrons and holes and provided excellent solubility in common organic solvents. A synthetic strategy is presented for the dielectric constant enhancement of organic semiconductors. It is demonstrated that fullerene derivatives, DPP‐ and PPV‐based polymers show a marked increase of the relative dielectric constant when being functionalized with TEG side chains. Density functional theory calculations attribute such enhancements to the rapid reorientations of ethylene glycol ­dipoles on the side chains.
      PubDate: 2014-10-14T11:30:36.51344-05:0
      DOI: 10.1002/adfm.201402244
  • Plasmonic Janus‐Composite Photocatalyst Comprising Au and
           C–TiO2 for Enhanced Aerobic Oxidation over a Broad
           Visible‐Light Range
    • Authors: Lequan Liu; Thang Duy Dao, Rajesh Kodiyath, Qing Kang, Hideki Abe, Tadaaki Nagao, Jinhua Ye
      Pages: n/a - n/a
      Abstract: Asymmetric Janus nanostructures containing a gold nanocage (NC) and a carbon–titania hybrid nanocrystal (AuNC/(C–TiO2)) are prepared using a novel and facile microemulsion‐based approach that involves the assistance of ethanol. The localized surface plasmon resonance of the Au NC with a hollow interior and porous walls induce broadband visible‐light harvesting in the Janus AuNC/(C–TiO2). An acetone evolution rate of 6.3 μmol h−1 g−1 is obtained when the Janus nanostructure is used for the photocatalytic aerobic oxidation of iso‐propanol under visible light (λ = 480–910 nm); the rate is 3.2 times the value of that obtained with C–TiO2, and in photo‐electrochemical investigations an approximately fivefold enhancement is obtained. Moreover, when compared with the core–shell structure (AuNC@(C–TiO2) and a gold–carbon–titania system where Au sphere nanoparticles act as light‐harvesting antenna, Janus AuNC/(C–TiO2) exhibit superior plasmonic enhancement. Electromagnetic field simulation and electron paramagnetic resonance results suggest that the plasmon–photon coupling effect is dramatically amplified at the interface between the Au NC and C–TiO2, leading to enhanced generation of energetic hot electrons for photocatalysis. A novel and facile approach is developed for preparing asymmetric Janus nanostructures comprising a gold nanocage and carbon–titania hybrid nanoparticles. The microemulsion‐based preparation, results in composites with increased plasmon–photon coupling at the interface of the AuNC and C–TiO2 particle. The amplification of the plasmon–photon coupling leads to enhanced generation of energetic hot electrons for visible‐light photocatalysis.
      PubDate: 2014-10-14T11:28:39.121274-05:
      DOI: 10.1002/adfm.201402088
  • Organic Thin Film Transistors Based on Highly Dipolar Donor–Acceptor
           Polymethine Dyes
    • Authors: Andreas Liess; Lizhen Huang, Alhama Arjona‐Esteban, Aifeng Lv, Marcel Gsänger, Vladimir Stepanenko, Matthias Stolte, Frank Würthner
      Pages: n/a - n/a
      Abstract: Organic thin film transistors (OTFTs) of a series of twenty dipolar donor–acceptor‐substituted polymethine dyes (D–A dyes, dipole moments from 3–15 D) are investigated. The employed merocyanine dyes contain a dimethine bridge that is substituted with 1‐alkyl‐3,3‐dimethylindolin‐2‐ylidene (“Fischer base”), 3‐alkyl‐2,3‐dihydrobenzothiazol‐2‐ylidene or 1,3‐benzodithiole‐2‐ylidene, respectively, as electron‐donating unit and various acceptor heterocycles. These studies show that thin films formed by these D–A dyes upon deposition in high vacuum are all composed of antiparallel π‐stacked dimers. However, they are either amorphous, discontinuous or highly crystalline due to the interplay between molecule‐substrate and dimer–dimer interactions. With the help of single crystal X‐ray analysis, out‐of‐plane X‐ray studies (XRD), selected area electron diffraction (SAED), and atomic force microscopy (AFM), a correlation between the molecular structure, film ordering, and hole charge transport ability can be established. The mobility values are compared to Bässler's disorder charge transport theory and a film growth mechanism is proposed based on DFT calculations and single crystal structures. The results show that with carefully adjusted bulky substituents and high dipolarity an intimate centrosymmetric packing with a slipped, but tight π‐stacking arrangement could be realized. This provides two‐dimensional percolation pathways for holes and ultimately results in charge carrier mobilities up to 0.18 cm2 V−1 s−1. Twenty dipolar donor–acceptor‐substituted polymethine dyes (merocyanines) are investigated as active layer in organic thin film transistors. It is shown that the diverse performance of the devices can be attributed to either low or high dimensional ordering in the crystal structure which in the latter case leads to mobilities as high as 0.18 cm2 V−1 s−1.
      PubDate: 2014-10-13T12:17:06.207026-05:
      DOI: 10.1002/adfm.201402678
  • Significantly Enhanced Thermoelectric Performance in n‐type
           Heterogeneous BiAgSeS Composites
    • Authors: Di Wu; Yanling Pei, Zhe Wang, Haijun Wu, Li Huang, Li‐Dong Zhao, Jiaqing He
      Pages: n/a - n/a
      Abstract: High performance n‐type bulk BiAgSeS is successfully synthesized to construct heterogeneous composites which consist of mesoscale grains of both pristine BiAgSeS and doped BiAgSeS1‐xClx (x = 0.03 or 0.05). Without perceptibly deteriorating the Seebeck coefficient, a significant enhancement on electrical conductivity is obtained due to an anomalous increase of both carrier mobility and concentration; the enhanced carrier mobility is proven to be a direct result of modulation doping which relates to the band alignments, while the increased carrier concentration is attributed to the possible charge transfer from Cl rich nanoscale precipitates at the heterogeneous BiAgSeS/BiAgSeS1‐xClx grain boundaries. Eventually, an enhanced figure of merit ZT ≈ 1.23 at 773 K in the composite (BiAgSeS)0.5(BiAgSeS0.97Cl0.03)0.5 is achieved, indicating that heterogeneous composites ultilizing the mechanism of modulation doping shall be a promising means of boosting the performance of thermoelectric materials. This strategy should be very likely applicable to other thermoelectrics. Charge carriers swimming in matrix grains free of ionized impurites in undoped region in the notion of modulation doping leads to a significant enhancement on power factor over the uniformly doped counterpart.
      PubDate: 2014-10-13T12:15:40.19518-05:0
      DOI: 10.1002/adfm.201402211
  • Facile Photo‐Crosslinking of Azide‐Containing
           Hole‐Transporting Polymers for Highly Efficient,
           Solution‐Processed, Multilayer Organic Light Emitting Devices
    • Authors: Junwoo Park; Changyeon Lee, Jihye Jung, Hyunbum Kang, Ki‐Hyun Kim, Biwu Ma, Bumjoon J. Kim
      Pages: n/a - n/a
      Abstract: A novel framework of azide containing photo‐crosslinkable, conducting copolymer, that is, poly(azido‐styrene)‐random‐poly(triphenylamine) (X‐PTPA), is reported as a hole‐transporting material for efficient solution‐processed, multi‐layer, organic light emitting diodes (OLEDs). A facile and energy‐efficient crosslinking process is demonstrated with UV irradiation (254 nm, 2 mW/cm2) at a short exposure time (5 min). By careful design of X‐PTPA, in which 5 mol% of the photo‐crosslinkable poly(azido‐styrene) is copolymerized with hole‐transporting poly(triphenylamine) (X‐PTPA‐5), the adverse effect of the crosslinking of azide moieties is prevented to maximize the performances of X‐PTPA‐5. Since the photo‐crosslinking chemistry of azide molecules does not involve any photo‐initiators, superior hole‐transporting ability is achieved, producing efficient devices. To evaluate the performances of X‐PTPA‐5 as a hole‐transporting/electron‐blocking layer, Ir(ppy)3‐based, solution‐processable OLEDs are fabricated. The results show high EQE (11.8%), luminous efficiency (43.7 cd/A), and power efficiency (10.4 lm/W), which represent about twofold enhancement over the control device without X‐PTPA‐5 film. Furthermore, micro‐patterned OLEDs with the photo‐crosslinkable X‐PTPA‐5 can be fabricated through standard photolithography. The versatility of this approach is also demonstrated by introducing the same azide moiety into other hole‐transporting materials such as poly(carbazole) (X‐PBC). Photo‐crosslinkable azide (N3) containing X‐PTPA is used as a HTL/EBL layer for highly efficient, solution‐processed multi‐layer OLEDs. The X‐PTPA with 5 mol% of N3 group can be fully crosslinked via mild UV irradiation at short exposure time. A twofold enhancement of device performance is realized with X‐PTPA layer over the control device. This photo‐crosslinkable HTL/EBL layer also allows the fabrication of micro‐pixelated multi‐layer OLEDs by photolithography.
      PubDate: 2014-10-13T12:15:35.432484-05:
      DOI: 10.1002/adfm.201401958
  • Blue Aggregation‐Induced Emission Luminogens: High External Quantum
           Efficiencies Up to 3.99% in LED Device, and Restriction of the Conjugation
           Length through Rational Molecular Design
    • Authors: Jing Huang; Ning Sun, Jie Yang, Runli Tang, Qianqian Li, Dongge Ma, Zhen Li
      Pages: n/a - n/a
      Abstract: Great efforts have been devoted to seek novel approaches for constructing blue fluorescent materials, which is one of the most important prerequisites for the commercialization of OLEDs. In recent years, various outstanding luminogens with aggregation‐induced emission characteristic exhibit promising applications as emitters, but blue AIE fluorophores with excellent EL performance are still very scarce. Here, five hole‐dominated blue AIE molecules are demonstrated by adopting construction approaches of changing linkage modes and increasing intramolecular torsion together, with the aim to restrict conjugation lengths without sacrificing good EL data. Device results show that the novel synthesized materials could be applied as bifunctional materials, namely blue light‐emitting and hole‐transporting materials, with comparable EL efficiencies, and the ηC,max and ηext,max are up to 8.03 cd A−1 and 3.99% respectively, which is among the best EL performance for blue AIE luminogens. Five hole‐dominated blue AIE molecules, constructed from TPA core and TPE derivatives peripheries, are successfully synthesized and served as hole‐transport layers and emitters for non‐doped blue OLEDs with current efficiencies up to 8.03 cd A−1. By adopting construction approaches of changing linkage modes and increasing intramolecular torsion together, the conjugation lengths are effectively shortened for ensuring blue emission.
      PubDate: 2014-10-13T12:15:30.560198-05:
      DOI: 10.1002/adfm.201401867
  • pH‐Responsive Cyanine‐Grafted Graphene Oxide for Fluorescence
           Resonance Energy Transfer‐Enhanced Photothermal Therapy
    • Authors: Miao Guo; Jie Huang, Yibin Deng, He Shen, Yufei Ma, Mengxin Zhang, Aijun Zhu, Yanli Li, He Hui, Yangyun Wang, Xiangliang Yang, Zhijun Zhang, Huabing Chen
      Pages: n/a - n/a
      Abstract: Stimuli‐responsive anticancer agents are of particular interest in the field of cancer therapy. Nevertheless, so far stimuli‐responsive photothermal agents have been explored with limited success for cancer photothermal therapy (PTT). In this work, as a proof‐of‐concept, a pH‐responsive photothermal nanoconjugate for enhanced PTT efficacy, in which graphene oxide (GO) with broad NIR absorbance and effective photothermal conversion efficiency is selected as a typical model receptor of fluorescence resonance energy transfer (FRET), and grafted cyanine dye (e.g., Cypate) acts as the donor of near‐infrared fluorescence (NIRF), is reported for the first time. The conjugate of Cypate‐grafted GO exhibits different conformations in aqueous solutions at various pH, which can trigger pH‐dependent FRET effect between GO and Cypate and thus induce pH‐responsive photothermal effect of GO‐Cypate. GO‐Cypate exhibits severe cell damage owing to the enhanced photothermal effect in lysosomes, and thus generate synergistic PTT efficacy with tumor ablation upon photoirradiation after a single‐dose intravenous injection. The photothermal nanoconjugate with broad NIR absorbance as the effective receptor of FRET can smartly convert emitted NIRF energy from donor cyanine dye into additional photothermal effect for improving PTT. These results suggest that the smart nanoconjugate can act as a promising stimuli‐responsive photothermal nanoplatform for cancer therapy. A smart cyanine‐grafted GO nanoconjugate (GO‐Cypate) with pH‐dependent FRET effect, which triggers pH‐responsive photothermal effect and thus results in enhanced PTT efficacy with tumor ablation upon NIR irradiation after a single‐dose intravenous injection, is reported.
      PubDate: 2014-10-13T11:57:13.800737-05:
      DOI: 10.1002/adfm.201402762
  • Injectable Peptide Decorated Functional Nanofibrous Hollow Microspheres to
           Direct Stem Cell Differentiation and Tissue Regeneration
    • Authors: Zhanpeng Zhang; Melanie J. Gupte, Xiaobing Jin, Peter X. Ma
      Pages: n/a - n/a
      Abstract: Injectable microspheres are attractive stem cell carriers for minimally invasive procedures. For tissue regeneration, the microspheres need to present the critical cues to properly direct stem cell differentiation. In natural extracellular matrix (ECM), growth factors (GFs) and collagen nanofibers provide critical chemical and physical cues. However, there have been no reported technologies that integrate synthetic nanofibers and GFs into injectable microspheres. In this study, functional nanofibrous hollow microspheres (FNF‐HMS), which can covalently bind GF‐mimicking peptides, are synthesized. Two different GF‐mimicking peptides, Transforming Growth Factor‐β1 mimicking peptide Cytomodulin (CM) and Bone Morphogenetic Protein‐2 mimicking peptide P24, are separately conjugated onto the FNF‐HMS to induce distinct differentiation pathways of rabbit bone marrow‐derived mesenchymal stem cells (BMSCs). While no existing biomaterials are reported to successfully deliver CM to induce chondrogenesis, the developed FNF‐HMS are shown to effectively present CM to BMSCs and successfully induced their chondrogenesis for ­cartilage formation in both in vitro and in vivo studies. In addition, P24 is conjugated onto the newly developed FNF‐HMS and is capable of retaining its bioactivity and inducing ectopic bone formation in nude mice. These results demonstrate that the novel FNF‐HMS can effectively deliver GF‐mimicking peptides to modulate stem cell fate and tissue regeneration. Functional nano‐fibrous hollow microspheres (FNF‐HMS) are developed to deliver growth factor mimics to stem cells with enhanced efficacy. When a TGF‐β1 mimicking peptide is conjugated, FNF‐HMS can serve as injectable stem cell carriers and induce chondrogenesis and cartilage formation. FNF‐HMS can also deliver BMP‐2 mimicking peptide to induce stem cell osteogenesis and bone formation.
      PubDate: 2014-10-13T11:57:11.295319-05:
      DOI: 10.1002/adfm.201402618
  • Long Passage Times of Short ssDNA Molecules through Metallized Nanopores
           Fabricated by Controlled Breakdown
    • Authors: Harold Kwok; Matthew Waugh, José Bustamante, Kyle Briggs, Vincent Tabard‐Cossa
      Pages: n/a - n/a
      Abstract: The fabrication of individual nanopores in metallized dielectric membranes using controlled breakdown directly in solution is described. Nanopores as small as 1.5‐nm in diameter are fabricated in Au‐coated silicon nitride membranes immersed in 1 m KCl by subjecting them to high electric fields. The physical and electrical characteristics of nanopores produced with this method are presented. The translocation of short single‐stranded DNA molecules is demonstrated through such nanopore devices without further passivation of the metallic surface. Metallized nanopores can prolong the translocation times of 50‐nt ssDNA fragments by as much as two orders of magnitude, while the slowest events can reach an average speed as slow as 2 nucleotides per millisecond. The mechanism for the long dwell‐time distribution is differentiated from prior studies, which relied on friction to slow down DNA, and is attributed to nucleotide‐Au interactions. Controlled breakdown (CBD) is used to fabricate a single nanometer‐scale hole, or nanopore, in Au‐coated silicon nitride membranes immersed in 1 m KCl and subjected to high electric fields. These metallized nanopores can extend the dwell times of 50‐nt ssDNA fragments by as much as two orders of magnitude, by relying on nucleoside‐Au interactions.
      PubDate: 2014-10-13T11:55:47.213658-05:
      DOI: 10.1002/adfm.201402468
  • Achieving Outstanding Mechanical Performance in Reinforced Elastomeric
           Composite Fibers Using Large Sheets of Graphene Oxide
    • Authors: Mohammad Ziabari Seyedin; Joselito M. Razal, Peter C. Innis, Rouhollah Jalili, Gordon G. Wallace
      Pages: n/a - n/a
      Abstract: A simple fiber spinning method used to fabricate elastomeric composite fibers with outstanding mechanical performance is demonstrated. By taking advantage of the large size of as‐prepared graphene oxide sheets (in the order of tens of micrometers) and their liquid crystalline behavior, elastomeric composite fibers with outstanding low strain properties have been fabricated without compromising their high strain properties. For example, the modulus and yield stress of the parent elastomer improved by 80‐ and 40‐fold, respectively, while maintaining the high extensibility of ∼400% strain inherent to the parent elastomer. This outstanding mechanical performance was shown to be dependent upon the GO sheet size. Insights into how both the GO sheet size dimension and dispersion parameters influence the mechanical behavior at various applied strains are discussed. A straightforward approach to prepare liquid crystalline dispersions of poly­urethane/graphene oxide (PU/GO) formulations has enabled the fabrication of high performance elastomeric composite fibers. The PU/GO fibers containing large GO sheets display remarkable reinforcement in modulus and yield stress (low strain properties) without compromising the extensibility and stretchability (high strain properties) inherent to PU. These fibers are produced using a very simple, continuous and highly scalable fiber wet‐spinning process.
      PubDate: 2014-10-13T11:55:42.393484-05:
      DOI: 10.1002/adfm.201402167
  • Hierarchically CdS Decorated 1D ZnO Nanorods‐2D Graphene Hybrids:
           Low Temperature Synthesis and Enhanced Photocatalytic Performance
    • Authors: Chuang Han; Zhang Chen, Nan Zhang, Juan Carlos Colmenares, Yi‐Jun Xu
      Pages: n/a - n/a
      Abstract: A simple, low‐temperature synthesis approach is reported for planting CdS‐sensitized 1D ZnO nanorod arrays on the 2D graphene (GR) sheet to obtain the ternary hierarchical nanostructures, during which graphene oxide (GO) as the precursor of GR acts as a flexible substrate for the formation of ZnO nanorod arrays. The hierarchical CdS‐1D ZnO‐2D GR hybrids can serve as an efficient visible‐light‐driven photocatalyst for selective organic transformations. The fast electron transport of 1D ZnO nanorods, the well‐known electronic conductivity of 2D GR, the intense visible‐light absorption of CdS, the unique hierarchical structure, and the matched energy levels of CdS, ZnO and GR efficiently boost the photogenerated charge carriers separation and transfer across the interfacial domain of hierarchical CdS‐1D ZnO‐2D GR hybrids under visible light irradiation via three‐level electron transfer process. Furthermore, the superior reusability of ternary hybrids is achieved by controlling the reaction parameters, i.e., using visible light irradiation and holes scavenger to prevent ZnO and CdS from photocorrosion. This work demonstrates a facile way of fabricating hierarchical CdS‐1D ZnO‐2D GR hybrids in a controlled manner and highlights a promising scope of adopting integrative photosensitization and co‐catalyst strategy to design more efficient semiconductor‐based composite photocatalysts toward solar energy capture and conversion. A facile, low‐temperature synthesis approach is reported to fabricate hierarchical CdS‐1D ZnO nanorod arrays‐2D graphene (GR) hybrids in a finely tailored manner in pursuit of the integration of the fast electron transport of 1D ZnO, the electron conductive platform of 2D graphene and the desirable visible‐light absorption of CdS to efficiently harvest visible light and boost the separation and transfer of the photogenerated charge carriers for specific photocatalytic applications.
      PubDate: 2014-10-13T11:52:28.354328-05:
      DOI: 10.1002/adfm.201402443
  • Voltage‐Controlled Nonstoichiometry in Oxide Thin Films:
           Pr0.1Ce0.9O2−δ Case Study
    • Authors: Di Chen; Harry L. Tuller
      Pages: n/a - n/a
      Abstract: While the properties of functional oxide thin films often depend strongly on oxygen stoichiometry, there have been few means available for its control in a reliable and in situ fashion. This work describes the use of DC bias as a means of systematically controlling the stoichiometry of oxide thin films deposited onto yttria‐stabilized zirconia substrates. Impedance spectroscopy is performed on the electrochemical cell Pr0.1Ce0.9O2−δ (PCO)/YSZ/Ag for conditions: T = 550 to 700 °C, pO 2 = 10−4 to 1 atm, and ΔE = ‐100 to 100 mV. The DC bias ΔE is used to control the effective pO 2 or oxygen activity at the PCO/YSZ interface. The non‐stoichiometry (δ) of the PCO films is calculated from the measured chemical capacitance (Cchem ). These δ values, when plotted isothermally as a function of effective pO 2, established, either by the surrounding gas composition alone, or in combination with applied bias, agree well with each other and to predictions based on a previously determined defect model. These results confirm the suitability of using bias to precisely control δ of thin films in an in situ fashion and simultaneously monitor these changes by measurement of Cchem . Of further interest is the ability to reach effective pO 2s as high as 280 atm. The non‐stoichiometry of oxide thin films is systematically controlled by use of DC bias. The suitability of using bias across an electrochemical cell to conveniently and precisely control non‐stoichiometry of oxide thin films, in an in situ fashion, and simultaneously monitor these changes by measurement of the chemical capacitance, is confirmed.
      PubDate: 2014-10-09T12:32:06.794541-05:
      DOI: 10.1002/adfm.201402050
  • Quasi‐Three‐Dimensional Angle‐Tolerant Electromagnetic
           Illusion Using Ultrathin Metasruface Coatings
    • Authors: Zhi Hao Jiang; Douglas H. Werner
      Pages: n/a - n/a
      Abstract: Low‐profile and light‐weight coatings that offer comprehensive manipulation of the electromagnetic scattering for finite‐length objects are highly desirable, but not yet achieved, for applications including camouflaging, deceptive sensing, radar cognition control, and defense security. Here, for the first time, the theory, practical design, and experimental demonstration of quasi‐three‐dimensional and angle‐tolerant electromagnetic illusion coatings are presented which have been enabled by ultrathin single‐layer functional metasurfaces. By controlling the multiple Mie scattering coefficients using the tangential and non‐vanishing radial electromagnetic responses of the metasurface, the quasi‐two‐dimensional coating transforms the electromagnetic perception of one object to mimic that of another which has been pre‐selected by the designer. The illusion coating, which is homogeneous but anisotropic, is realized using hundreds of composite electric and magnetic sub‐wavelength unit cells operating at frequencies away from their resonance. Two different prototypes of the metasurface illusion coatings were fabricated and characterized, demonstrating very good camouflaging performance for finite‐length dielectric as well as conducting objects within a field‐of‐view up to ±10° off normal. This work paves the way for practical artificially engineered material coatings with exotic and versatile scattering control capabilities that would enable a wide range of applications throughout the entire electromagnetic spectrum. Quasi‐three‐dimensional and angle‐tolerant electromagnetic illusion coatings are proposed, designed, and demonstrated using ultrathin single‐layer functional metasurfaces with nonvanishing radial response. The quasi‐two‐dimensional metasurface coatings transform the electromagnetic perception of one object to mimic that of another which has been pre‐selected by the designer. The illusion coating is realized using hundreds of composite electric and magnetic sub‐wavelength unit cells.
      PubDate: 2014-10-09T12:32:01.637235-05:
      DOI: 10.1002/adfm.201401561
  • Self‐Powered Trajectory, Velocity, and Acceleration Tracking of a
           Moving Object/Body using a Triboelectric Sensor
    • Authors: Fang Yi; Long Lin, Simiao Niu, Jin Yang, Wenzhuo Wu, Sihong Wang, Qingliang Liao, Yue Zhang, Zhong Lin Wang
      Pages: n/a - n/a
      Abstract: Motion tracking is of great importance in a wide range of fields such as automation, robotics, security, sports and entertainment. Here, a self‐powered, single‐electrode‐based triboelectric sensor (TES) is reported to accurately detect the movement of a moving object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the movement of an object on the top surface of a polytetrafluoroethylene (PTFE) layer induces changes in the electrical potential of the patterned aluminum electrodes underneath. From the measurements of the output performance (open‐circuit voltage and short‐circuit current), the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values. Moreover, the TES can detect motions of more than one objects moving at the same time. In addition, applications of the TES are demonstrated by using LED illuminations as real‐time indicators to visualize the movement of a sliding object and the walking steps of a person. A self‐powered, single‐electrode‐based triboelectric sensor is reported to accurately detect the movement of an object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values.
      PubDate: 2014-10-06T23:57:42.538047-05:
      DOI: 10.1002/adfm.201402703
  • Hybrid CuTCNQ/AgTCNQ Metal‐Organic Charge Transfer Complexes via
           Galvanic Replacement vs Corrosion‐Recrystallization
    • Authors: Andrew Pearson; Rajesh Ramanathan, Anthony P. O'Mullane, Vipul Bansal
      Pages: n/a - n/a
      Abstract: This study reports a hybrid of two metal‐organic semiconductors that are based on organic charge transfer complexes of 7,7,8,8‐tetracyanoquinodimethane (TCNQ). It is shown that the spontaneous reaction between semiconducting microrods of CuTCNQ with Ag+ ions leads to the formation of a CuTCNQ/AgTCNQ hybrid, both in aqueous solution and acetonitrile, albeit with completely different reaction mechanisms. In an aqueous environment, the reaction proceeds by a complex galvanic replacement (GR) mechanism, wherein in addition to AgTCNQ nanowires, Ag0 nanoparticles and Cu(OH)2 crystals decorate the surface of CuTCNQ microrods. Conversely, in acetonitrile, a GR mechanism is found to be thermodynamically unfavorable and instead a corrosion‐recrystallization mechanism leads to the decoration of CuTCNQ microrods with AgTCNQ nanoplates, resulting in a pure CuTCNQ/AgTCNQ hybrid metal‐organic charge transfer complex. While hybrids of two different inorganic semiconductors are regularly reported, this report pioneers the formation of a hybrid involving two metal‐organic semiconductors that will expand the scope of TCNQ‐based charge transfer complexes for improved catalysis, sensing, electronics, and biological applications. A new metal organic semiconductor hybrid of CuTCNQ and AgTCNQ is reported. The synthesis of these hybrids in water and acetonitrile reveal two completely unexpected and different mechanisms in these solvents. A facile generalized approach to prepare hybrid materials comprising two metal‐TCNQs in a single system will expand the applicability of TCNQ‐based charge transfer complexes to new applications.
      PubDate: 2014-10-06T06:15:42.052483-05:
      DOI: 10.1002/adfm.201402320
  • Multi‐Shell Porous TiO2 Hollow Nanoparticles for Enhanced Light
           Harvesting in Dye‐sensitized Solar Cells
    • Authors: Sun Hye Hwang; Juyoung Yun, Jyongsik Jang
      Pages: n/a - n/a
      Abstract: An optimized configuration for nanomaterials in working electrodes is vital to the high performance of dye‐sensitized solar cells (DSSCs). Here, a fabrication method is introduced for multi‐shell TiO2 hollow nanoparticles (MS‐TiO2‐HNPs) via a sol–gel reaction, calcination, and an etching process. The prepared uniform MS‐HNPs have a high surface area (ca. 171 m2 g−1), multireflection, and facile electrolyte circulation and diffusion. During the MS‐HNP fabrication process, the amount of SiO2 precursor and H2O under reaction has a significant effect on aggregation and side reactions. The etching process to obtain pure TiO2 is influenced by anatase crystallinity. Additionally, single‐shell (SS)‐TiO2‐HNPs and double‐shell (DS)‐TiO2‐HNPs are synthesized as a control. The MS‐TiO2‐HNPs exhibit a high surface area and enhance light reflectance, compared with the SS‐ and DS‐TiO2‐HNPs of the same size. The power conversion efficiency of the optimized MS‐TiO2‐HNP‐based DSSCs is 9.4%, compared with the 8.0% efficiency demonstrated by SS‐TiO2‐HNP‐DSSCs (a 17.5% improvement). These results enable the utilization of multifunctional MS‐HNPs in energy material applications, such as lithium ion batteries, photocatalysts, water‐splitting, and supercapacitors. Multi‐shell porous TiO2 hollow nanoparticles (MS‐TiO2‐HNPs) are prepared by a sol–gel method and calcination and etching processes. Due to the porous multi‐shell structure, the MS‐TiO2‐HNPs exhibit strong light scattering and facile electrolyte diffusion and circulation. Additionally, the high surface area increases the adsorption of the dye molecules to the surface of the MS‐TiO2‐HNPs, resulting in an enhanced power conversion efficiency of 9.4%.
      PubDate: 2014-10-06T06:15:35.308165-05:
      DOI: 10.1002/adfm.201401915
  • Directed Electric Field Z‐Alignment Kinetics of Anisotropic
           Nanoparticles for Enhanced Ionic Conductivity
    • Authors: Saurabh Batra; Emre Unsal, Miko Cakmak
      Pages: n/a - n/a
      Abstract: In this study, the fast transient evolution of the electric field assisted thickness Z‐direction orientation and assembly of clay particles is studied using a instrumented real time system that simultaneously measures in‐plane and out of plane birefringence. The optical anisotropy master curves are developed, connecting the exposure time and electric field strength with orientation, using a superposition principle. Z‐oriented nanocomposite films manufactured through the R2R process show enhancement through thickness ionic conductivity, useful for membranes of batteries and fuel cells. Kinetics of electric field induced alignment of anisotropic particles through the thickness of polymer film is studied using birefringence. Kinetics of alignment is used to determine the processing conditions to create continuous oriented films using roll‐to‐roll manufacturing process. The directional percolation of these particles enhances thickness properties creating functional films for membranes and flexible electronics.
      PubDate: 2014-10-06T06:15:30.704751-05:
      DOI: 10.1002/adfm.201400760
  • Intracellular Microenvironment‐Responsive Dendrimer‐Like
           Mesoporous Nanohybrids for Traceable, Effective, and Safe Gene Delivery
    • Authors: Xin Du; Lin Xiong, Sheng Dai, Freddy Kleitz, Shi Zhang Qiao
      Pages: n/a - n/a
      Abstract: In order to create advanced functional nanocarriers for efficient gene therapy, novel intracellular microenvironment‐sensitive fluorescence label‐free nanostructured dendrimer‐like silica hybrid nanocarriers are developed for traceable, effective, and safe gene delivery. Dendrimer‐like mesoporous silica nanoparticles (DMSNs) with center‐radial large pores are covalently modified with short polyethyleneimine (PEI) for efficient gene loading and binding. Autofluorescent and biodegradable PEI (AC‐PEI) responsive to the intracellular microenvironment are then coated on the gene‐loaded nanoparticles for inhibiting gene leakage from the carriers. Moreover, AC‐PEI coating not only endows intracellular microenvironment‐responsive gene release property, but also allows monitoring the gene delivery process in the absence of external labelling, owing to the pH‐ and GSH‐responsive autofluorescence and biodegradability of AC‐PEI. The resultant nanocarriers show high gene loading capacity, low cytotoxicity, stimuli‐responsive gene release, label‐free, and simultaneous fluorescence tracking, and high gene silencing capability. Thus, these developed nanocarriers hold substantial and promising potential as effective and safe gene‐delivery carriers for future scientific investigation and practical implications in gene therapy. Novel intracellular microenvironment‐sensitive fluorescence label‐free nanostructured dendrimer‐like silica hybrid nanocarriers are successfully developed to achieve traceable, effective, and safe gene delivery. The pH‐ and GSH‐responsive autofluorescent and biodegradable properties of the coated polymer not only endow a responsive gene release property, but also allow real‐time monitoring of the gene delivery process.
      PubDate: 2014-10-06T06:06:43.817505-05:
      DOI: 10.1002/adfm.201402408
  • Bio‐Inspired, Water‐Soluble to Insoluble Self‐Conversion
           for Flexible, Biocompatible, Transparent, Catecholamine Polysaccharide
           Thin Films
    • Authors: Ji Hyun Ryu; Seongyeon Jo, Mi‐Young Koh, Haeshin Lee
      Pages: n/a - n/a
      Abstract: In nature, a variety of functional water‐insoluble organic materials are biologically synthesized in aqueous conditions without chemical additives and organic solvents. Insect cuticle, crustacean shells, and many others are representative examples. The insoluble materials are prepared by enzyme reactions and programmed self‐assembly in water from water‐soluble precursors. If the water‐basis could be adapted, environment‐friendly strategy developed in nature, many problems caused by the vast consumption of petroleum‐based olefin materials could be solved or significantly attenuated. Here, the spontaneous formation of water‐insoluble, biocompatible films from a water‐soluble polymer is demonstrated without using any chemical additives and organic solvents. It is found that a water‐soluble chitosan–catechol polymeric precursor is spontaneously self‐converted to flexible water‐insoluble thin film by simple dehydration. The preparation of mechanically robust, water‐insoluble, flexible, transparent chitosan–catechol film is a completely unexpected result because most water‐soluble polymers exist as powders when dehydrated. The film can be used as a bag similar to polyvinyl one and is multifunctional and biocompatible for drug delivery depots and tissue engineering applications. The water‐basis, environment‐friendly strategy evolutionarilly optimized in nature can solve problems shown in the widely implemented petroleum‐based olefin materials. Here, the spontaneous formation of water‐insoluble, biocompatible microfilms from a water‐soluble polymer is demonstrated without using any chemical additives similar to the biological process shown in the insect cuticle formation.
      PubDate: 2014-10-06T06:06:38.004306-05:
      DOI: 10.1002/adfm.201402250
  • Chain Length Dependence of the Photovoltaic Properties of Monodisperse
           Donor–Acceptor Oligomers as Model Compounds of Polydisperse Low Band
           Gap Polymers
    • Authors: Cheng Zhou; Yamin Liang, Feng Liu, Chen Sun, Xuelong Huang, Zengqi Xie, Fei Huang, Jean Roncali, Thomas P. Russell, Yong Cao
      Pages: n/a - n/a
      Abstract: Well‐defined conjugated oligomers (Sn) containing from 1 to 8 units of a tricyclic building block involving a dioctyloxybenzothiadiazole unit with two thienyl side rings (S1) are synthesized by a bottom‐up approach. UV–Vis absorption data of solutions show that chain extension produces a narrowing of the HOMO–LUMO gap (ΔE) to values slightly smaller than that of the parent polymer (P1). Plots of ΔE and of the band gap of films (E g) versus the reciprocal chain length show that ΔE and E g converge towards a limit corresponding to an effective conjugation length (ECL) of 7–8 S1 units. UV–Vis absorption and photoluminescence data of solutions and solid films show that chain extension enhances the propensity to inter‐chain aggregation. This conclusion is confirmed by GIXD analyses which reveal that the edge‐on orientation of short‐chain systems evolves toward a face‐on orientation as chain length increases while the π‐stacking distance decreases beyond 7 units. The results obtained on solution‐processed BHJ solar cells show a progressive improvement of power conversion efficiency (PCE) with chain extension; however, the convergence limit of PCE remains inferior to that obtained with the polymer. These results are discussed with regard to the role of mono/polydispersity and chain aggregation. A series of donor–acceptor monodisperse oligomers (S1 –S8) and two analogous polydisperse polymers (P1, P2) are synthesized successfully. These materials serve as a model system to understand the relationship between conjugation length and the photophysical, morphological, and photovoltaic properties in donor–acceptor polymer solar cell materials, and provide a bridge between small molecules and the polymers.
      PubDate: 2014-10-06T05:56:21.120346-05:
      DOI: 10.1002/adfm.201401945
  • Understanding the Role of Underlayers and Overlayers in Thin Film Hematite
    • Authors: Ludmilla Steier; Isaac Herraiz‐Cardona, Sixto Gimenez, Francisco Fabregat‐Santiago, Juan Bisquert, S. David Tilley, Michael Grätzel
      Pages: n/a - n/a
      Abstract: Recent research on photoanodes for photoelectrochemical water splitting has introduced the concept of under‐ and overlayers for the activation of ultrathin hematite films. Their effects on the photocatalytic behavior were clearly shown; however, the mechanism is thus far not fully understood. Herein, the contribution of each layer is analyzed by means of electrochemical impedance spectroscopy, with the aim of obtaining a general understanding of surface and interface modifications and their influence on the hematite photoanode performance. This study shows that doping of the hematite from the underlayer and surface passivation from annealing treatments and an overlayer are key parameters to consider for the design of more efficient iron oxide electrodes. Understanding the contribution of these layers, a new design for ultrathin hematite films employing a combination of a gallium oxide overlayer with thin niobium oxide and silicon oxide underlayers is shown to achieve a photocurrent onset potential for the photoelectrochemical oxidation of water more negative than 750 mV versus the reversible hydrogen electrode (RHE) at pH 13.6, utilizing Co‐Pi as a water oxidation catalyst. It is demonstrated that multilayer hematite thin film photoanodes are a strategy to reduce the overpotential for this material, thereby facilitating more efficient tandem cells. Impedance spectroscopy reveals new details for efficiency‐enhancing modifications of hematite water splitting photo­anodes. Suitable underlayers such as Nb2O5 and SiOx dramatically increase the conductivity in hematite ultrathin films, thereby improving the plateau photocurrent, and the photocurrent onset potential is determined by the energetic position and density of surface states, which can be modified by annealing and surface treatments.
      PubDate: 2014-10-02T02:06:08.86857-05:0
      DOI: 10.1002/adfm.201402742
  • First Principles Calculations of Charge Transfer Excitations in
           Polymer–Fullerene Complexes: Influence of Excess Energy
    • Authors: Dorota Niedzialek; Ivan Duchemin, Thiago Branquinho de Queiroz, Silvio Osella, Akshay Rao, Richard Friend, Xavier Blase, Stephan Kümmel, David Beljonne
      Pages: n/a - n/a
      Abstract: The ability of quantum simulations to predict the electronic structure at donor/acceptor interfaces and correlate it with the quantum efficiency of organic solar cells remains a major challenge. The need to describe with increased accuracy electron‐electron and electron‐hole interactions, while better accounting for disorder and environmental screening in realistic interfaces, requires significant progress to improve both the accuracy and computational efficiency of available quantum simulation methods. In the present study, the results of different ab initio techniques are compared, namely time‐dependent density functional and many‐body perturbation theories, with experimental data on three different polymer/fullerene heterojunctions. It is shown that valuable information concerning the thermodynamic drive for electron‐hole dissociation or recombination into triplets can be obtained from such calculations performed on model interfaces. In particular, the ability of these approaches to reproduce the Veldman and co–workers classification of the three studied interfaces is discussed, showing the success and limits of state‐of‐the‐art ab initio techniques. A comparative first‐principle study is presented of polymer‐fullerene complexes that differ by the excess energy for charge separation. The measured quantum efficiencies of the bulk heterojunctions can be traced back to the presence of energy‐accessible charge‐transfer states with large electron‐hole radii and molecular triplets mediating competing recombination pathways.
      PubDate: 2014-10-02T02:06:06.210499-05:
      DOI: 10.1002/adfm.201402682
  • 3D TEM Tomography of Templated Bilayer Films of Block Copolymers
    • Authors: Kevin W. Gotrik; Thomas Lam, Adam F. Hannon, Wubin Bai, Yi Ding, Jonathan Winterstein, Alfredo Alexander‐Katz, J. Alexander Liddle, Caroline A. Ross
      Pages: n/a - n/a
      Abstract: Transmission electron microscope (TEM) tomography was used to visualize the morphology and 3D connectivity of a lithographically templated, self‐assembled bilayer film of cylinder‐forming 45.5 kg/mol polystyrene‐block‐polydimethylsiloxane. The structure, formed after a 5 min solvothermal anneal, was imaged with a resolution of ≈3 nm in 3D, enabling a comparison between measurement and self‐consistent mean‐field theory (SCFT) calculations. Images of etched and unetched samples showed that etching collapsed the PDMS microdomain structure and reduced the template dimensions. In addition to the general comparison between modeled and measured dimensions, the tomography revealed connections between the orthogonal layers of cylinders at their crossing points. Comparison with the SCFT model, even under solvothermal annealing conditions, shows that it is helpful in understanding the detailed nanoscale structure of features created by directed self‐assembly (DSA), which is essential in developing nanomanufacturing processes based on DSA. Understanding the 3D structure of self‐assembled block copolymer films is essential to their applications in nanolithography. The 3D microdomain structure of a block copolymer consisting of polydimethylsiloxane cylindrical domains in a polystyrene matrix, templated by posts, is determined by TEM tomography. The cylinders form a cross‐point array (left), which is compared with the predictions of self‐consistent field theory (right).
      PubDate: 2014-10-02T02:06:03.15494-05:0
      DOI: 10.1002/adfm.201402457
  • Photosystem I‐based Biophotovoltaics on Nanostructured Hematite
    • Authors: Kasim Ocakoglu; Tomasz Krupnik, Bart van den Bosch, Ersan Harputlu, Maria Pia Gullo, Julian David Janna Olmos, Saadet Yildirimcan, Ram K. Gupta, Fahrettin Yakuphanoglu, Andrea Barbieri, Joost N. H. Reek, Joanna Kargul
      Pages: n/a - n/a
      Abstract: The electronic coupling between a robust red algal photosystem I (PSI) associated with its light harvesting antenna (LHCI) and nanocrystalline n‐type semiconductors, TiO2 and hematite (α‐Fe2O3) is utilized for fabrication of the biohybrid dye‐sensitized solar cells (DSSC). PSI‐LHCI is immobilized as a structured multilayer over both semiconductors organized as highly ordered nanocrystalline arrays, as evidenced by FE‐SEM and XRD spectroscopy. Of all the biohybrid DSSCs examined, α‐Fe2O3/PSI‐LHCI biophotoanode operates at a highest quantum efficiency and generates the largest open circuit photo­current compared to the tandem system based on TiO2/PSI‐LHCI material. This is accomplished by immobilization of the PSI‐LHCI complex with its reducing side towards the hematite surface and nanostructuring of the PSI‐LHCI multilayer in which the subsequent layers of this complex are organized in the head‐to‐tail orientation. The biohybrid PSI‐LHCI‐DSSC is capable of sustained photoelectrochemical H2 production upon illumination with visible light above 590 nm. Although the solar conversion efficiency of the PSI‐LHCI/hematite DSSC is currently below a practical use, the system provides a blueprint for a genuinely green solar cell that can be used for molecular hydrogen production at a rate of 744 μmoles H2 mg Chl−1 h−1, placing it amongst the best performing biohybrid solar‐to‐fuel nanodevices. A fully integrated, stable and functional photosystem I‐based biohybrid dye‐sensitized solar cell is constructed with an improved solar‐to‐electric quantum efficiency over previously reported biohybrid devices. A highly robust oriented Cyanidioschyzon merolae PSI‐LHCI complex is used as a natural photosensitizer of the nanostructured hematite substrate for the sustained photodriven H2 production.
      PubDate: 2014-10-02T02:05:46.842898-05:
      DOI: 10.1002/adfm.201401399
  • Tailoring Electron‐Transfer Barriers for Zinc Oxide/C60 Fullerene
    • Authors: Philip Schulz; Leah L. Kelly, Paul Winget, Hong Li, Hyungchul Kim, Paul F. Ndione, Ajaya K. Sigdel, Joseph J. Berry, Samuel Graham, Jean‐Luc Brédas, Antoine Kahn, Oliver L. A. Monti
      Pages: n/a - n/a
      Abstract: The interfacial electronic structure between oxide thin films and organic semiconductors remains a key parameter for optimum functionality and performance of next‐generation organic/hybrid electronics. By tailoring defect concentrations in transparent conductive ZnO films, we demonstrate the importance of controlling the electron transfer barrier at the interface with organic acceptor molecules such as C60. A combination of electron spectroscopy, density functional theory computations, and device characterization is used to determine band alignment and electron injection barriers. Extensive experimental and first principles calculations reveal the controllable formation of hybridized interface states and charge transfer between shallow donor defects in the oxide layer and the molecular adsorbate. Importantly, it is shown that removal of shallow donor intragap states causes a larger barrier for electron injection. Thus, hybrid interface states constitute an important gateway for nearly barrier‐free charge carrier injection. These findings open new avenues to understand and tailor interfaces between organic semiconductors and transparent oxides, of critical importance for novel optoelectronic devices and applications in energy‐conversion and sensor technologies. Controlling the defect composition of the oxide surface allows the barriers to be changed for charge transfer at the ZnO/Fullerene interface. Direct and inverse electron spectroscopy is used to demonstrate the control over the transfer barrier by tracking electronic alignment and interface state formation. This is predicted by DFT and leads to observable alterations in charge injection in our devices.
      PubDate: 2014-10-01T11:41:06.29142-05:0
      DOI: 10.1002/adfm.201401794
  • Highly Stretchable Conductors Integrated with a Conductive Carbon
           Nanotube/Graphene Network and 3D Porous Poly(dimethylsiloxane)
    • Authors: Mengting Chen; Ling Zhang, Shasha Duan, Shilong Jing, Hao Jiang, Chunzhong Li
      Pages: n/a - n/a
      Abstract: Here, a novel and facile method is reported for manufacturing a new stretchable conductive material that integrates a hybrid three dimensional (3D) carbon nanotube (CNT)/reduced graphene oxide (rGO) network with a porous poly(dimethylsiloxane) (p‐PDMS) elastomer (pPCG). This reciprocal architecture not only alleviates the aggregation of carbon nanofillers but also significantly improves the conductivity of pPCG under large strains. Consequently, the pPCG exhibits high electrical conductivity with a low nanofiller loading (27 S m−1 with 2 wt% CNTs/graphene) and a notable retention capability after bending and stretching. The simulation of the mechanical properties of the p‐PDMS model demonstrates that an extremely large applied strain (εappl) can be accommodated through local rotations and bending of cell walls. Thus, after a slight decrease, the conductivity of pPCG can continue to remain constant even as the strain increases to 50%. In general, this architecture of pPCG with a combination of a porous polymer substrate and 3D carbon nanofiller network possesses considerable potential for numerous applications in next‐generation stretchable electronics. A highly stretchable conductor is manufactured by integrating porous poly(dimethylsiloxane) (p‐PDMS) with a CNT/graphene network (pPCG). Mechanical simulation of p‐PDMS demonstrates that large strains are accommodated through strut rotations and bending. After a slight decrease, the high conductivity (27 S m−1 with 2 wt% CNTs/graphene) remained constant, even as the strain was increased to 50%.
      PubDate: 2014-10-01T11:40:45.705075-05:
      DOI: 10.1002/adfm.201401886
  • Intranuclear Photosensitizer Delivery and Photosensitization for Enhanced
           Photodynamic Therapy with Ultralow Irradiance
    • Authors: Limin Pan; Jianan Liu, Jianlin Shi
      Pages: n/a - n/a
      Abstract: Photodynamic therapy (PDT) is a well‐established clinical treatment modality for various diseases. However, reactive oxygen species (ROS) generated by photosensitizers(PS) under proper irradiation exhibits the extremely short life span (
      PubDate: 2014-09-30T13:49:27.502667-05:
      DOI: 10.1002/adfm.201402255
  • Direct Growth of Nanographene on Silicon with Thin Oxide Layer for
           High‐Performance Nanographene‐Oxide‐Silicon Diodes
    • Authors: Qichong Zhang; Xiaojuan Wang, Dong Li, Zengxing Zhang
      Pages: n/a - n/a
      Abstract: Graphene‐silicon based configurations are attracting great attention for their potential application as electronics and optoelectronics. For their practical use, it is still limited by the configuration fabrication process. In this paper, a catalyst‐free method is reported to directly grow nanographene on silicon covered with a thin oxide layer to form nanographene‐oxide‐silicon configurations. Compared with previously reported nanographene‐silicon Schottky junctions, the nanographene‐oxide‐silicon structures exhibit a high performance on electronic and photovoltaic properties. The reverse leakage current of the nanographene‐oxide‐silicon is suppressed from over 10−5 A down to 10−8 A and the rectifier ratio is greatly enhanced from less than 5 up to 103. The photovoltage is enhanced over 50 times. The nanographene‐oxide‐silicon structures exhibit especially ultrasensitive to weak light at a photovoltage working mode, which exceeds up to 106 V/W at the light power of 0.025 μW. Due to the source material for nanographene is photoresist and the fabrication process is mainly based on the current‐used photolithography and silicon technique, the developed nanographene‐oxide‐silicon structures are very easy for device fabrication, integration, and miniaturization, and could be a promising way to produce metal‐free graphene‐silicon based electronics and optoelectronics for commercial use. A simple and low cost approach of directly producing high‐performance metal‐free nanographene‐oxide‐silicon diodes is developed. The nanographene is from photoresist without any transfer and the approach is based on the conventional photolithography and silicon technique. Due to the source material is photoresist, the fabrication approach is easy for device fabrication, integration and miniaturization, and thus for commercial use.
      PubDate: 2014-09-30T13:48:49.789173-05:
      DOI: 10.1002/adfm.201402099
  • Optimization of Solubility, Film Morphology and Photodetector Performance
           by Molecular Side‐Chain Engineering of Low‐Bandgap
           Thienothiadiazole‐Based Polymers
    • Authors: Ji Qi; Xiaokang Zhou, Dezhi Yang, Wenqiang Qiao, Dongge Ma, Zhi Yuan Wang
      Pages: n/a - n/a
      Abstract: A series of donor–acceptor (D‐A) type low‐bandgap polymers containing the terthiophene and thieno[3,4‐b]thiadiazole units in the main chain but different numbers of identical side chains are designed and synthesized in order to study the effect of side chain on the polymer properties and optimize the performance of polymer photodetectors. Variation in the side chain content can influence the polymer solubility, molecular packing, and film morphology, which in turn affects the photodetector performance, particularly with regard to the photoresponsivity and dark current. X‐ray diffraction patterns indicate that molecular ordering increases with more side chains. Atomic force microscopy shows that appropriate morphology of the active layer in the polymer photodetector is necessary for high photocurrent and low dark current. Using BCP as a hole blocking layer (10 nm), the photodetector based on P4 exhibits the optimized performance with specific detectivity of 1.4 × 1012 Jones at 800 nm, which is among the best reported values for polymer photodetectors and even comparable to that of a silicon photodetector. A series of thieno[3,4‐b]thiadiazole based low‐bandgap polymers with different amounts of side chains are designed for probing the effect of side chains on solubility, molecular packing, film morphology, and key performance of polymer photodetectors. Among them, the P4‐based photodetector demonstrates the best performance and shows fairly constant specific detectivity of about 1012 Jones in the spectral range of 330–950 nm.
      PubDate: 2014-09-30T13:48:39.452231-05:
      DOI: 10.1002/adfm.201401948
  • Joule Heating Characteristics of Emulsion‐Templated Graphene
    • Authors: Robert Menzel; Suelen Barg, Miriam Miranda, David B. Anthony, Salem M. Bawaked, Mohamed Mokhtar, Shaeel A. Al‐Thabaiti, Sulaiman N. Basahel, Eduardo Saiz, Milo S. P. Shaffer
      Pages: n/a - n/a
      Abstract: The Joule heating properties of an ultralight nanocarbon aerogel are investigated with a view to potential applications as energy‐efficient, local gas heater, and other systems. Thermally reduced graphene oxide (rGO) aerogels (10 mg cm−3) with defined shape are produced via emulsion‐templating. Relevant material properties, including thermal conductivity, electrical conductivity and porosity, are assessed. Repeatable Joule heating up to 200 °C at comparatively low voltages (≈1 V) and electrical power inputs (≈2.5 W cm−3) is demonstrated. The steady‐state core and surface temperatures are measured, analyzed and compared to analogous two‐dimensional nanocarbon film heaters. The assessment of temperature uniformity suggests that heat losses are dominated by conductive and convective heat dissipation at the temperature range studied. The radial temperature gradient of an uninsulated, Joule‐heated sample is analyzed to estimate the aerogel's thermal conductivity (around 0.4 W m−1 K−1). Fast initial Joule heating kinetics and cooling rates (up to 10 K s−1) are exploited for rapid and repeatable temperature cycling, important for potential applications as local gas heaters, in catalysis, and for regenerable of solid adsorbents. These principles may be relevant to wide range of nanocarbon networks and applications. A fundamental study of the direct resistive heating of graphene aerogels demonstrates efficient, uniform, fast, and repeatable Joule heating. The outlined principles pave a route towards new applications of three‐dimensional nanocarbon networks as viable light‐weight, high‐surface‐area local gas heaters and temperature‐controlled catalyst and adsorber supports.
      PubDate: 2014-09-30T13:48:22.466152-05:
      DOI: 10.1002/adfm.201401807
  • Wafer Scale Synthesis and High Resolution Structural Characterization of
           Atomically Thin MoS2 Layers
    • Authors: Aaron S. George; Zafer Mutlu, Robert Ionescu, Ryan J. Wu, Jong S. Jeong, Hamed H. Bay, Yu Chai, K. Andre Mkhoyan, Mihrimah Ozkan, Cengiz S. Ozkan
      Pages: n/a - n/a
      Abstract: Synthesis of atomically thin MoS2 layers and its derivatives with large‐area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated‐ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV–Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X‐ray photo­emission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high‐angle annular dark‐field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back‐gate field‐effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2‐WS2 thin layers. Wafer scale synthesis of atomically thin MoS2 layers via thermolysis of spin coated films is presented. High resolution characterization of atomically thin layers is performed by HAADF‐STEM image analysis. This approach could be applied to a variety of substrates and provides a promising route towards wafer scale production of other TMD and doped materials for applications in electronics and optoelectronics.
      PubDate: 2014-09-30T13:44:12.124433-05:
      DOI: 10.1002/adfm.201402519
  • Green Emission in Ladder‐Type Quarterphenyl: Beyond the
    • Authors: Björn Kobin; Francesco Bianchi, Simon Halm, Joachim Leistner, Sylke Blumstengel, Fritz Henneberger, Stefan Hecht
      Pages: n/a - n/a
      Abstract: In polyfluorenes it is generally accepted that (photo)degradation leads to fluorenone type defects that accept the excitation energy and emit green‐to‐yellow light with rather low efficiency. Although initial spectroscopic studies suggest the same to hold true for ladder‐type poly(para‐phenylene)s (LPPPs), kinetic studies of the degradation process are not compatible with the established mechanism. In general, the observed green emission can be caused by the introduction of carbonyl groups; however, only if associated with an additional disruption of the backbone rigidity and hence planarity of the entire π‐system. This is clearly shown by comparison with synthesized model compounds, which are bearing the fluorenone motif yet possess very different optical properties as compared to the defects, which are actually formed. Degradation can be caused by solvent specific, yet substrate nonspecific aromatic formylation but mainly originates from reaction with in‐situ generated singlet oxygen, both in solution as well as in thin films. Time‐dependent photoluminescence measurements on thin films show that green emission is enhanced by energy transfer from intact molecules to defect centers. Photodegradation in polyfluorenes has traditionally been explained by fluorenone‐type defects. Thorough analysis of the photodegradation products of ladder‐type quarter­phenyl and comparison with separately synthesized, potential ketone products now shows that the observed green emission indeed originates from the introduction of carbonyl groups yet only if associated with an additional disruption of the backbone rigidity and hence planarity of the π‐system.
      PubDate: 2014-09-30T13:43:48.780968-05:
      DOI: 10.1002/adfm.201402638
  • Nano‐Bio‐Chemical Braille for Cells: The Regulation of Stem
           Cell Responses using Bi‐Functional Surfaces
    • Authors: Wojciech Chrzanowski; Jae Ho Lee, Alexey Kondyurin, Megan S. Lord, Jun‐Hyeog Jang, Hae‐Won Kim, Marcela M. M. Bilek
      Pages: n/a - n/a
      Abstract: Insufficient integration with local host tissues is a significant problem that adversely affects the performance of implanted biomedical devices. Poor tissue integration leaves patients susceptible to complications associated with adverse foreign body reactions and infections that typically mandate expensive and elevated‐risk revision surgery. The aging population and growing incidence of medical implants makes the development of bio‐functional implant surfaces a high priority research imperative. Here multifunctional surfaces are reported that are capable of regulating cell adhesion and triggering cell differentiation to facilitate osseointegration of implantable devices. The approach described is universal, cost‐ and time‐effective. It relies on a unique combination of two advances: i) a reactive interface provided by a plasma activated coating (PAC) that covalently immobilises bioactive molecules with significantly higher efficiency than conventional technologies, and ii) multifunctional molecules (bi‐functional fusion‐proteins) that regulate multiple cellular responses. Covalent linking of the molecules, their high density, and desired orientation are demonstrated. The effectiveness of these functional interfaces to regulate mesenchymal stem cell attachment and differentiation is confirmed suggesting the ability to regulate osseointegration. This method is a leap forward in the fabrication of truly biofunctional materials tailored for particular applications. A single step technology that activates the surfaces of biomedical implant materials is developed to enable the direct covalent immobilization of novel bi‐functional proteins via the formation of highly reactive radicals embedded in the surface. This multifunctional interface successfully regulates mesenchymal stem cell adhesion and differentiation at the surface, thus resulting in an osteoinductive surface that enhances implant integration within the body.
      PubDate: 2014-09-30T04:16:42.206589-05:
      DOI: 10.1002/adfm.201401696
  • Laser‐Activatible PLGA Microparticles for Image‐Guided Cancer
           Therapy In Vivo
    • Authors: Yang Sun; Yanjie Wang, Chengcheng Niu, Eric M. Strohm, Yuanyi Zheng, Haitao Ran, Rongzhong Huang, Di Zhou, Yuping Gong, Zhigang Wang, Dong Wang, Michael C. Kolios
      Pages: n/a - n/a
      Abstract: Poly(lactide‐co‐glycolic acid) (PLGA) particles are biocompatible and bio­degradable, and can be used as a carrier for various chemotherapeutic drugs, imaging agents and targeting moieties. Micrometer‐sized PLGA particles were synthesized with gold nanoparticles and DiI dye within the PLGA shell, and perfluorohexane liquid (PFH) in the core. Upon laser irradiation, the PLGA shell absorbs the laser energy, activating the liquid core (liquid conversion to gas). The rapidly expanding gas is expelled from the particle, resulting in a microbubble; this violent process can cause damage to cells and tissue. Studies using cell cultures show that PLGA particles phagocytosed by single cells are consistently vaporized by laser energies of 90 mJ cm−2, resulting in cell destruction. Rabbits with metastasized squamous carcinoma in the lymph nodes are then used to evaluate the anti‐cancer effects of these particles in the lymph nodes. After percutaneous injection of the particles and upon laser irradiation, through the process of optical droplet vaporization, ultrasound imaging shows a significant increase in contrast in comparison to the control. Histology and electron microscopy confirm damage with disrupted cells throughout the lymph nodes, which slows the tumor growth rate. This study shows that PLGA particles containing PFC liquids can be used as theranostic agents in vivo. PLGA particles containing gold nano­particles/DiI dye in the shell and perfluorohexane in the core are investigated as intravenous theranostic agents. Upon laser irradiation, the liquid core violently vaporizes into a microbubble, damaging nearby tissue. A tumor region can be selectively targeted in vivo, and the vaporization process verified through an increase in contrast during ultrasound imaging.
      PubDate: 2014-09-29T02:50:01.962985-05:
      DOI: 10.1002/adfm.201402631
  • Photoresponsive Soft‐Robotic Platform: Biomimetic Fabrication and
           Remote Actuation
    • Authors: Weitao Jiang; Dong Niu, Hongzhong Liu, Chaohui Wang, Tingting Zhao, Lei Yin, Yongsheng Shi, Bangdao Chen, Yucheng Ding, Bingheng Lu
      Pages: n/a - n/a
      Abstract: Biomimetic microsystems, which can be driven by various stimuli, are an emerging field in micro/nano‐technology and nano‐medicine. In this study, a soft and fast‐response robotic platform, constituted by PDMS/graphene‐nanoplatelets composited layer (PDMS/GNPs) and pristine PDMS layer, is presented. Due to the differences in coefficient of thermal expansion and Young's modulus of the two layers, the bilayer platform can be driven to bend to the PDMS/GNPs side by light irradiation. The robotic platform (1 mm in width and 7 mm in length) can be deflected about 1500 μm by near infrared irradiation (nIR)(808 nm in wavelength) within 3.4 s, and excellent reversibility and repeatability in actuation are also revealed by sweeping and multicycle light irradiation. The experiments also show that, the presented bilayer platform in various shapes, that is, fish‐like shapes, can float and swim to perspective location in fluid (i.e., water), whose moving directions and velocities can be remotely adjusted by light, indicating an excellent light‐actuation ability and well controllability. The results may be not only hopeful in developing light‐driven drug‐delivery platform, but also the bio‐robotic microgrippers applying in vivo and in vitro. Soft and fast‐response robotic platform constituted by PDMS/graphene‐nanoplatelets composited layer (PDMS/GNPs) and pristine PDMS layer are proposed. The robotic platform can be driven by near infrared irradiation (nIR) due to the photothermal effect of graphene to mimic the fish swimming, which is hopeful in developing light‐driven drug‐delivery platform, but also the bio‐robotic microgrippers applying in vivo and in vitro.
      PubDate: 2014-09-29T02:49:58.236213-05:
      DOI: 10.1002/adfm.201402070
  • Ortho‐ vs Bay‐Functionalization: a Comparative Study on
    • Authors: Glauco Battagliarin; Sreenivasa Reddy Puniredd, Sebastian Stappert, Wojciech Zajaczkowski, Suhao Wang, Chen Li, Wojciech Pisula, Klaus Müllen
      Pages: n/a - n/a
      Abstract: In this paper n‐type semiconductors synthesized via selective fourfold cyanation of the ortho‐ and bay‐positions (2,5,10,13‐ and 1,6,9,14‐positions respectively) of teyrrylenediimides are reported. A detailed study about the impact of the diverse functionalization topologies on the optoelectronic properties, self‐organization from solution, solid‐state packing, and charge carrier transport in field‐effect transistors is presented. The ortho‐substitution preserves the planarity of the core and favors high order in solution processed films. However, the strong intermolecular interactions lead to a microstructure with large aggregates and pronounced grain boundaries which lower the charge carrier transport in transistors. In contrast, the well‐soluble bay‐functionalized terrylenediimide forms only disordered films which surprisingly result in n‐type average mobilities of 0.17 cm2/Vs after drop‐casting with similar values in air. Processing by solvent vapor diffusion enhances the transport to 0.65 cm2/Vs by slight improvement of the order and surface arrangement of the molecules. This mobility is comparable to highest n‐type conductivities measured for solution processed PDI derivatives demonstrating the high potential of TDI‐based semiconductors. Ortho‐ vs Bay‐Functionalization: a Comparative Study on Tetracyano‐TerrylenediimidesOrtho‐ or bay‐tetracyanation? A comparative study on terrylenediimide reveals that the two functionalizations have similar impact on the optoelectronic properties, but remarkably different effects on self‐assembling from solution, with striking consequences on the n‐type behavior in field‐effect transistors. The pronounced electron mobilities here reported for the bay‐tetracyano derivative demonstrate the high potential of terrylenediimide as scaffold for n‐type semiconductors.
      PubDate: 2014-09-29T02:48:56.64124-05:0
      DOI: 10.1002/adfm.201401573
  • Insulator‐Conductor Type Transitions in Graphene‐Modified
           Silver Nanowire Networks: A Route to Inexpensive Transparent Conductors
    • Authors: Izabela Jurewicz; Azin Fahimi, Phillip E. Lyons, Ronan J. Smith, Maria Cann, Matthew L. Large, Mingwen Tian, Jonathan N. Coleman, Alan B. Dalton
      Pages: n/a - n/a
      Abstract: Silver nanowire coatings are an attractive alternative to indium tin oxide for producing transparent conductors. To fabricate coatings with low sheet resistance required for touchscreen displays, a multi‐layer network of silver nanowires must be produced that may not be cost effective. This problem is counteracted here by modifying the electrical properties of an ultra‐low‐density nanowire network through local deposition of conducting graphene platelets. Unlike other solution‐processed materials, such as graphene oxide, our pristine graphene is free of oxygen functional groups, resulting in it being electrically conducting without the need for further chemical treatment. Graphene adsorption at inter‐wire junctions as well as graphene connecting adjacent wires contributes to a marked enhancement in electrical properties. Using our approach, the amount of nanowires needed to produce viable transparent electrodes could be more than 50 times less than the equivalent pristine high density nanowire networks, thus having major commercial implications. Using a laser ablation process, it is shown that the resulting films can be patterned into individual electrode structures, which is a pre‐requisite to touchscreen sensor fabrication. A simple, scalable, and relatively inexpensive method is described for preparing highly conducting AgNW/graphene hybrid transparent electrodes that use low‐cost solution‐processed pristine graphene. A combination of spray deposition and Langmuir‐based techniques is used to produce ultrathin films with controlled nanowire and graphene densities. The results indicate that these graphene/nanowire hybrid films may serve as a cheap replacement for existing technologies in electronic devices.
      PubDate: 2014-09-26T02:45:43.572227-05:
      DOI: 10.1002/adfm.201402547
  • Memristor Kinetics and Diffusion Characteristics for Mixed
           Anionic‐Electronic SrTiO3‐δ Bits: The
           Memristor‐Based Cottrell Analysis Connecting Material to Device
    • Authors: Felix Messerschmitt; Markus Kubicek, Sebastian Schweiger, Jennifer L.M. Rupp
      Pages: n/a - n/a
      Abstract: Memristors based on mixed anionic‐electronic conducting oxides are promising devices for future data storage and information technology with applications such as non‐volatile memory or neuromorphic computing. Unlike transistors solely operating on electronic carriers, these memristors rely, in their switch characteristics, on defect kinetics of both oxygen vacancies and electronic carriers through a valence change mechanism. Here, Pt SrTiO3‐δ Pt structures are fabricated as a model material in terms of its mixed defects which show stable resistive switching. To date, experimental proof for memristance is characterized in hysteretic current–voltage profiles; however, the mixed anionic‐electronic defect kinetics that can describe the material characteristics in the dynamic resistive switching are still missing. It is shown that chronoamperometry and bias‐dependent resistive measurements are powerful methods to gain complimentary insights into material‐dependent diffusion characteristics of memristors. For example, capacitive, memristive and limiting currents towards the equilibrium state can successfully be separated. The memristor‐based Cottrell analysis is proposed to study diffusion kinetics for mixed conducting memristor materials. It is found that oxygen diffusion coefficients increase up to 3 × 10–15 m2s–1 for applied bias up to 3.8 V for SrTiO3‐δ memristors. These newly accessible diffusion characteristics allow for improving materials and implicate field strength requirements to optimize operation towards enhanced performance metrics for valence change memristors. The strategy for studying material‐dependent diffusion characteristics for mixed conducting memristors is extended by applying chronoamperometry and bias‐dependent resistive measurements. The memristor‐based Cottrell analysis and equation is proposed to derive oxygen diffusion coefficients of 3 × 10‐15 m2s‐1 for bias increase up to 3.8 V for SrTiO3‐δ memristors at room temperature.
      PubDate: 2014-09-25T06:34:05.601165-05:
      DOI: 10.1002/adfm.201402286
  • Ultrasensitive Plasmonic Response of Bimetallic Au/Pd Nanostructures to
    • Authors: Ruibin Jiang; Feng Qin, Qifeng Ruan, Jianfang Wang, Chongjun Jin
      Pages: n/a - n/a
      Abstract: Hydrogen detection is crucial for the safety of all hydrogen‐related applications. Compared to electrical hydrogen sensors, which usually suffer from possible electric sparks, optical hydrogen sensors offer advantages of remote and contact‐free readout and therefore the avoidance of spark generation. Herein, bimetallic Au/Pd nanostructure monolayers that exhibit ultrasensitive plasmonic response to hydrogen are reported. Bimetallic Au/Pd nanostructures with continuous and discontinuous Pd shells are prepared. The plasmonic response to hydrogen is monitored by measuring the extinction spectra of the ensemble Au/Pd nanostructures deposited on glass slides. Introduction of hydrogen induces red plasmon shifts, which become larger for the nanostructures with thicker Pd shells. For the nanostructures with continuous Pd shell, the plasmon shift can reach 56 nm at the hydrogen volume concentration below the explosion limit. The plasmon resonance wavelength displays an excellent linear dependence on the hydrogen volume concentration below 1%. The detection limit in the experiments reaches 0.2%. The nanostructures with discontinuous Pd shell show smaller plasmon shifts than those with continuous Pd shell. The extinction measurements on the ensemble nanostructures supported on transparent substrates and the unprecedentedly large plasmon shifts and sensitivity make the results very promising for the development of practical optical hydrogen sensors. The plasmonic response of bimetallic Au/Pd nanostructures to hydrogen is systematically investigated. Red plasmon shifts larger than 50 nm are observed when Au/Pd nanostructure monolayers are exposed to hydrogen at the volume concentration below the explosion limit. The facile measurements and ultrasensitive plasmonic response make the bimetallic nanostructures very promising for the development of practical optical hydrogen sensors.
      PubDate: 2014-09-24T06:15:11.925307-05:
      DOI: 10.1002/adfm.201402091
  • High‐Performance Hybrid Supercapacitor Enabled by a High‐Rate
           Si‐based Anode
    • Authors: Ran Yi; Shuru Chen, Jiangxuan Song, Mikhail L. Gordin, Ayyakkannu Manivannan, Donghai Wang
      Pages: n/a - n/a
      Abstract: A hybrid supercapacitor constructed of a Si‐based anode and a porous carbon cathode is demonstrated with both high power and energy densities. Boron‐doping is employed to improve the rate capability of the Si‐based anode (B‐Si/SiO2/C). At a high current density of 6.4 A/g, B‐Si/SiO2/C delivers a capacity of 685 mAh/g, 2.4 times that of the undoped Si/SiO2/C. Benefiting from the high rate performance along with low working voltage, high capacity, and good cycling stability of B‐Si/SiO2/C, the hybrid supercapacitor exhibits a high energy density of 128 Wh/kg at 1229 W/kg. Even when power density increases to the level of a conventional supercapacitor (9704 W/kg), 89 Wh/kg can be obtained, the highest values of any hybrid supercapacitor to date. Long cycling life (capacity retention of 70% after 6000 cycles) and low self‐discharge rate (voltage retention of 82% after 50 hours) are also achieved. This work opens an avenue for development of high‐performance hybrid supercapacitors using high‐performance Si‐based anodes. A hybrid supercapacitor is constructed of a high‐rate Si‐based anode and a porous carbon cathode. The hybrid supercapacitor exhibits a high energy density of 128 Wh/kg at 1229 W/kg. Even when power density increases to the level of a conventional supercapacitor (9704 W/kg), 89 Wh/kg can be obtained. Long cycling life and low self‐discharge rate are also achieved.
      PubDate: 2014-09-22T07:20:47.522239-05:
      DOI: 10.1002/adfm.201402398
  • General Formation of MS (M = Ni, Cu, Mn) Box‐in‐Box Hollow
           Structures with Enhanced Pseudocapacitive Properties
    • Authors: Xin‐Yao Yu; Le Yu, Laifa Shen, Xiaohui Song, Hongyu Chen, Xiong Wen (David) Lou
      Pages: n/a - n/a
      Abstract: Complex hollow structures of metal sulfides could be promising materials for energy storage devices such as supercapacitors and lithium‐ion batteries. However, it is still a great challenge to fabricate well‐defined metal sulfides hollow structures with multi‐shells, hierarchical architectures, and non‐spherical shape. In this work, a template‐engaged strategy is developed to synthesize hierarchical NiS box‐in‐box hollow structures with double‐shells. The NiS box‐in‐box hollow structures constructed by ultrathin nanosheets are evaluated as electrode materials for supercapacitors. As expected, the NiS box‐in‐box hollow structures exhibit excellent rate performance and impressive cycling stability due to their unique nano‐architecture. More importantly, the synthetic method can be easily extended to synthesize other transition metal sulfides box‐in‐box hollow structures. For example, we have also successfully synthesized similar CuS and MnS box‐in‐box hollow structures. The present work makes a significant contribution to the design and synthesis of transition metal sulfides hollow structures with non‐spherical shape and complex architecture, as well as their potential applications in electrochemical energy storage. Box in box: A template‐engaged method is successfully developed to synthesize hierarchical metal sulfide (NiS, CuS, MnS) box‐in‐box hollow structures with double‐shells. As an example, it is demonstrated that the NiS box‐in‐box hollow structure exhibits excellent pseudocapacitive performance with remarkable rate performance and cycling stability.
      PubDate: 2014-09-22T07:17:13.039836-05:
      DOI: 10.1002/adfm.201402560
  • Charge Carrier Localization and Transport in Organic Semiconductors:
           Insights from Atomistic Multiscale Simulations
    • Authors: Marko Mladenović; Nenad Vukmirović
      Pages: n/a - n/a
      Abstract: Organic electronic semiconducting materials exhibit complex atomic structures with a lack of periodicity that lead to charge carrier localization which, in turn, strongly affects the electronic transport properties of these materials. To understand charge carrier localization and electronic transport in organic semiconductors, simulations that take into account the details of the atomic structure of the material are of utmost importance. In this article, computational methods that can be used to simulate the electronic properties of organic semiconductors are reviewed and an overview of the results that have been obtained from such simulations is given. Using these methods the effects of static disorder, thermal disorder and interfaces between domains are investigated and the microscopic origin of these effects is identified. It is shown that in strongly disordered conjugated polymer materials the main origin of the localization of charge carrier wave functions is the disordered long‐range electrostatic potential. In ordered polymers, thermal disorder of main chains leads to wave function localization. In small molecule based organic semiconductors, grain boundaries introduce localized trap states at the points where electronic coupling is the strongest. It is also demonstrated that detailed atomistic simulations are necessary for quantitative and sometimes even qualitative description of charge mobility in organic materials. Organic semiconductor materials exhibit different types of disorder which lead to localization of charge carrier wave functions. Atomic multiscale simulations can be used to generate the models of atomic structure and to calculate the wave function localization lengths, electronic density of states and sometimes even the conductivity of the material.
      PubDate: 2014-09-22T03:24:42.613553-05:
      DOI: 10.1002/adfm.201402435
  • All Solution‐Processed Chalcogenide Solar Cells – from Single
           Functional Layers Towards a 13.8% Efficient CIGS Device
    • Authors: Yaroslav E. Romanyuk; Harald Hagendorfer, Patrick Stücheli, Peter Fuchs, Alexander R. Uhl, Carolin M. Sutter‐Fella, Melanie Werner, Stefan Haass, Josua Stückelberger, Cédric Broussillou, Pierre‐Philippe Grand, Veronica Bermudez, Ayodhya N. Tiwari
      Pages: n/a - n/a
      Abstract: Solution processing of inorganic thin films has become an important thrust in material research community because it offers low‐cost and high‐throughput deposition of various functional coatings and devices. Especially inorganic thin film solar cells – macroelectronic devices that rely on consecutive deposition of layers on large‐area rigid and flexible substrates – could benefit from solution approaches in order to realize their low‐cost nature. This article critically reviews existing deposition approaches of functional layers for chalcogenide solar cells with an extension to other thin film technologies. Only true solutions of readily available metal salts in appropriate solvents are considered without the need of pre‐fabricated nanoparticles. By combining three promising approaches, an air‐stable Cu(In,Ga)Se2 thin film solar cell with efficiency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from solutions. Notably, water is employed as the solvent in all steps, highlighting the potential for safe manufacturing with high utilization rates. A Cu(In,Ga)Se2 thin film solar cell with efficiency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from aqueous solutions of metal salts using industrially scalable processes.
      PubDate: 2014-09-19T06:14:09.809095-05:
      DOI: 10.1002/adfm.201402288
  • Highly Efficient and Robust Blue Phosphorescent Pt(II) Compounds with a
           Phenyl‐1,2,3‐triazolyl and a
           Pyridyl‐1,2,4‐triazolyl Chelate Core
    • Authors: Xiang Wang; Shao‐Long Gong, Datong Song, Zheng‐Hong Lu, Suning Wang
      Pages: n/a - n/a
      Abstract: A new class of brightly phosphorescent Pt(II) compounds that contain an N∧C‐chelate phenyl‐1,2,3‐triazolyl ligand (ptrz) and an N∧C‐chelate pyridyl‐1,2,4‐triazolyl ligand (pytrz) in the central core is achieved. The impact of various substituent groups on phosphorescence of this class of molecules is examined. Crystal structural analyses revealed that this class of compounds has a great tendency to form stacked dimers—one of which is persistent even in the gas phase—leading to excimer emission. The introduction of bulky substituents, such as diphenyl amino (NPh2) or trityl (CPh3), is found to greatly diminish the excimer emission. Using this approach, several highly efficient blue and green phosphorescent Pt(II) compounds with λem at ≈450–460 nm and Φp ≈ 0.70 to 1.00 are obtained. These molecules are highly robust with exceptionally high thermal stability. Bright bluish‐green electrophosphorescent devices with external quantum efficiencies as high as 16.7% are fabricated. Bright blue and green phosphorescent Pt(II) complexes with an N∧C chelate 1,2,3‐triazolyl ligand and an N∧N chelate 1,2,4‐trizolyl ligand, near unity quantum efficiencies and high thermal stability are achieved. Steric blocking and the rigidity enhancement around the Pt(II) core by large substituent groups at the para‐position are found to be critical in the bright phosphorescence of this new class of compounds.
      PubDate: 2014-09-18T06:34:16.709229-05:
      DOI: 10.1002/adfm.201402366
  • Dendrimer‐Encapsulated Ruthenium Oxide Nanoparticles as Catalysts in
           Lithium‐Oxygen Batteries
    • Authors: Priyanka Bhattacharya; Eduard N. Nasybulin, Mark H. Engelhard, Libor Kovarik, Mark E. Bowden, Xiaohong S. Li, Daniel J. Gaspar, Wu Xu, Ji‐Guang Zhang
      Pages: n/a - n/a
      Abstract: Dendrimer‐encapsulated ruthenium oxide nanoparticles (DEN‐RuO2) have been used as catalysts in lithium‐oxygen (Li‐O2) batteries for the first time. The results obtained from ultraviolet‐visible spectroscopy, electron microscopy and X‐ray photoelectron spectroscopy show that the nanoparticles synthesized by the dendrimer template method are ruthenium oxide, not metallic ruthenium as reported by other groups. The DEN‐RuO2 significantly improves the cycling stability of Li‐O2 batteries with carbon electrodes and decreases the charging potential even at ten times less catalyst loading than those reported previously. The monodispersity, porosity, and large number of surface functionalities of the dendrimer template prevent the aggregation of the RuO2 nanoparticles, making their entire surface area available for catalysis. The potential of using DEN‐RuO2 as a standalone cathode material for Li‐O2 batteries is also explored. Dendrimer‐encapsulated ruthenium nano­particles are readily oxidized to RuO2 when exposed to ambient conditions. These nanoparticles are used as catalysts in Li‐O2 batteries, which exhibited improved cycling thus suggesting that porous dendrimer‐encapsulated nanoparticles can be used to achieve superior performance in energy storage systems.
      PubDate: 2014-09-17T07:27:25.718797-05:
      DOI: 10.1002/adfm.201402701
  • Rationally Designed Dynamic Protein Hydrogels with Reversibly Tunable
           Mechanical Properties
    • Authors: Na Kong; Qing Peng, Hongbin Li
      Pages: n/a - n/a
      Abstract: Protein hydrogels have attracted considerable interest due to their potential applications in biomedical engineering. Creating protein hydrogels with dynamic mechanical properties is challenging. Here, the engineering of a novel, rationally designed protein‐hydrogel is reported that translates molecular level protein folding‐unfolding conformational changes into macroscopic reversibly tunable mechanical properties based on a redox controlled protein folding‐unfolding switch. This novel protein folding switch is constructed from a designed mutually exclusive protein. Via oxidation and reduction of an engineered disulfide bond, the protein folding switch can switch its conformation between folded and unfolded states, leading to a drastic change of protein's effective chain length and mechanical compliance. This redox‐responsive protein can be readily photochemically crosslinked into solid hydrogels, in which molecular level conformational changes (folding‐unfolding) can result in significant macroscopic changes in hydrogel's physical and mechanical properties due to the change of the effective chain length between two crosslinking points in the protein hydrogel network. It is found that when reduced, the hydrogel swells and is mechanically compliant; when oxidized, it swells to a less extent and becomes resilient and stiffer, exhibiting an up to fivefold increase in its Young's modulus. The changes of the mechanical and physical properties of this hydrogel are fully reversible and can be cycled using redox potential. This novel protein hydrogel with dynamic mechanical and physical properties could find numerous applications in material sciences and tissue engineering. Translating molecular events into macroscopic tunable mechanical properties: Using a redox potential‐controlled protein switch as a building block, protein‐based dynamic hydrogels are engineered. Upon redox potential‐controlled protein folding‐unfolding, these novel protein hydrogels exhibit dynamically tunable mechanical properties and can switch between a compliant state and a stiff yet resilient state.
      PubDate: 2014-09-17T07:27:09.252036-05:
      DOI: 10.1002/adfm.201402205
  • Pd‐Cu Bimetallic Tripods: A Mechanistic Understanding of the
           Synthesis and Their Enhanced Electrocatalytic Activity for Formic Acid
    • Authors: Lei Zhang; Sang‐Il Choi, Jing Tao, Hsin‐Chieh Peng, Shuifen Xie, Yimei Zhu, Zhaoxiong Xie, Younan Xia
      Pages: n/a - n/a
      Abstract: This article reports a facile synthesis of Pd‐Cu bimetallic tripods with a purity over 90%. Two requirements must be met in order to form tripods: i) formation of triangular, plate‐like seeds during the nucleation step and ii) preferential deposition of atoms onto the three corners of a seed during the growth step. In this synthesis, these requirements are fulfilled by adding CuCl2 and KBr into an aqueous synthesis. Specifically, it is demonstrated that the Cu atoms resulting from underpotential deposition could greatly reduce the energy barrier involved in the formation of triangular seeds with planar defects because of the much lower stacking fault energy (41 mJ·m−2 for Cu vs 220 mJ·m−2 for Pd). The Br− ions could strongly bind to the three {100} side faces of a triangular seed, forcing the Pd atoms to grow from the three corners of a seed to generate a tripod. When compared with commercial Pd black, the Pd‐Cu tripods exhibited substantially enhanced catalytic activity toward the electro‐oxidation of formic acid. This work offers a general strategy for the synthesis of nanocrystals with a tripod structure for catalytic applications. Pd‐Cu bimetallic tripods are prepared by adding CuCl2 and KBr into an aqueous synthesis that involves the reduction of a salt precursor by ascorbic acid. When compared with commercial Pd black, the Pd‐Cu tripods exhibit substantially enhanced (almost eight folds per unit mass of Pd) catalytic activity toward the electro‐oxidation of formic acid.
      PubDate: 2014-09-16T12:25:08.109714-05:
      DOI: 10.1002/adfm.201402350
  • Highly Conductive Microfiber of Graphene Oxide Templated Carbonization of
           Nanofibrillated Cellulose
    • Authors: Yuanyuan Li; Hongli Zhu, Fei Shen, Jiayu Wan, Xiaogang Han, Jiaqi Dai, Hongqi Dai, Liangbing Hu
      Pages: n/a - n/a
      Abstract: Microfibers with conductivity of 649 ± 60 S/cm are introduced through a carbonization of well‐aligned graphene oxide (GO) – nanofibrillated cellulose (NFC) hybrid fibers. GO acts as a template for NFC carbonization, which changes the morphology of carbonized NFC from microspheres to sheets while improving the carbonization of NFC. Meanwhile, the carbonized NFC repairs the defects of reduced GO (rGO) and links rGO sheets together. The GO templated carbonization of NFC as well as the alignment of the building blocks along the fiber direction leads to excellent conductivity. Conductive microfibers are evaluated as lithium ion battery anodes, which can be applied in wearable electronics. This approach to make conductive microfibers and the low cost raw materials used in this work may be applied to other carbon based conductive structures. Highly conductive microfibers are designed and fabricated with graphene oxide (GO) and nanofibrillated cellulose (NFC). The alignment of GO flakes and the templated carbonization of NFC leads to high electrical conductivity of ca. 650 S/cm.
      PubDate: 2014-09-16T01:59:28.797192-05:
      DOI: 10.1002/adfm.201402129
  • Stepped Moduli in Layered Composites
    • Authors: Ju‐Hee So; Alok S. Tayi, Firat Güder, George M. Whitesides
      Pages: n/a - n/a
      Abstract: This paper describes adaptive composites that respond to mechanical stimuli by changing their Young's modulus. These composites are fabricated by combining a shorter layer of elastic material (e.g., latex) and a longer layer of stiffer material (e.g., polyethylene and Kevlar), and fixing them together at their ends. Tension along the layered composite increases its length, and as the strain increases, the composite changes the load‐bearing layer from the elastic to the stiff material. The result is a step in the Young's modulus of the composite. The characteristics of the step (or steps) can be engineered by changing the constituent materials, the number of layers, and their geometries (e.g., sinusoidal, hierarchical, two‐dimensional web‐like, rod‐coil, embedded, and ring structures). For composites with more than two steps in modulus, the materials within the composites can be layered in a hierarchical structure to fit within a smaller volume, without sacrificing performance. These composites can also be used to make structures with tunable, stepped compressive moduli. An adaptation of these principles can generate an electronic sensor that can monitor the applied compressive strain. Increasing or decreasing the strain closes or opens a circuit and reversibly activates a light‐emitting diode. Adaptive Young's moduli of composites are demonstrated by combining different materials and controlling their geometries. As applied strain increases, the critical component that dictates the mechanical strength of the composite shifts from an elastic material to a stiff material, resulting in discrete steps in increasing moduli. The characteristics of the steps can be engineered to accommodate specific requirements of applications.
      PubDate: 2014-09-16T01:59:25.095635-05:
      DOI: 10.1002/adfm.201401548
  • Distinguishing the Importance of Fullerene Phase Separation from Polymer
           Ordering in the Performance of Low Band Gap Polymer:Bis‐Fullerene
    • Authors: Huipeng Chen; Yu‐Che Hsiao, Jihua Chen, Bin Hu, Mark Dadmun
      Pages: n/a - n/a
      Abstract: One way to improve power conversion efficiency (PCE) of polymer based bulk‐heterojunction (BHJ) photovoltaic cells is to increase the open circuit voltage (V oc). Replacing PCBM with bis‐adduct fullerenes significantly improves V oc and the PCE in devices based on the conjugated polymer poly(3‐hexyl thiophene) (P3HT). However, for the most promising low band‐gap polymer (LBP) system, replacing PCBM with ICBA results in poor short‐circuit current (J sc) and PCE although V oc is significantly improved. The optimization of the morphology of as‐cast LBP/bis‐fullerene BHJ photovoltaics is attempted by adding a co‐solvent to the polymer/fullerene solution prior to film deposition. Varying the solubility of polymer and fullerene in the co‐solvent, bulk heterojunctions are fabricated with no change of polymer ordering, but with changes in fullerene phase separation. The morphologies of the as‐cast samples are characterized by small angle neutron scattering and neutron reflectometry. A homogenous dispersion of ICBA in LBP is found in the samples where the co‐solvent is selective to the polymer, giving poor device performance. Aggregates of ICBA are formed in samples where the co‐solvent is selective to ICBA. The resultant morphology improves PCE by up to 246%. A quantitative analysis of the neutron data shows that the interfacial area between ICBA aggregates and its surrounding matrix is improved, facilitating charge transport and improving the PCE. The morphology of low band gap polymer:ICBA mixtures is efficiently controlled during film deposition by adding a co‐solvent. A morphology with ICBA phase separation is formed without a change in polymer ordering when a co‐solvent in which ICBA is selectively soluble is used. The resultant morphology improves power conversion efficiency by up to 246%.
      PubDate: 2014-09-16T01:59:22.463649-05:
      DOI: 10.1002/adfm.201401419
  • Theranostic USPIO‐Loaded Microbubbles for Mediating and Monitoring
           Blood‐Brain Barrier Permeation
    • Authors: Twan Lammers; Patrick Koczera, Stanley Fokong, Felix Gremse, Josef Ehling, Michael Vogt, Andrij Pich, Gert Storm, Marc van Zandvoort, Fabian Kiessling
      Pages: n/a - n/a
      Abstract: Efficient and safe drug delivery across the blood‐brain barrier (BBB) remains one of the major challenges of biomedical and (nano‐) pharmaceutical research. Here, it is demonstrated that poly(butyl cyanoacrylate)‐based microbubbles (MB), carrying ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles within their shell, can be used to mediate and monitor BBB permeation. Upon exposure to transcranial ultrasound pulses, USPIO‐MB are destroyed, resulting in acoustic forces inducing vessel permeability. At the same time, USPIO are released from the MB shell, they extravasate across the permeabilized BBB and they accumulate in extravascular brain tissue, thereby providing non‐invasive R 2*‐based magnetic resonance imaging information on the extent of BBB opening. Quantitative changes in R 2* relaxometry are in good agreement with 2D and 3D microscopy results on the extravascular deposition of the macromolecular model drug fluorescein isothiocyanate (FITC)‐dextran into the brain. Such theranostic materials and methods are considered to be useful for mediating and monitoring drug delivery across the BBB and for enabling safe and efficient treatment of CNS disorders. Polymer‐based microbubbles containing ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles within their shell can be used to simultaneously mediate and monitor blood‐brain barrier (BBB) permeation and to enable efficient macromolecular (model) drug delivery into the central nervous system.
      PubDate: 2014-09-16T01:59:19.945772-05:
      DOI: 10.1002/adfm.201401199
  • Light‐Powered Healing of a Wearable Electrical Conductor
    • Authors: Hong Suk Kang; Hee‐Tak Kim, Jung‐Ki Park, Seungwoo Lee
      Pages: n/a - n/a
      Abstract: Mechanical failure along a conductive pathway can cause unexpected shutdown of an electronic devices, ultimately limiting the device lifetime. To address this problem, various systems to realize healable electrical conductors have been proposed; however, rapid, noninvasive, and on‐demand healing, factors that are all synergistically required, especially for wearable device applications, still remains challenging. Here, a light‐powered healable electrical conductor (conceptualized as photofluidic diffusional system) is proposed for simple‐, fast‐, and easy‐to‐implement wearable devices (e.g., the electronic skin, sensitive to mechanical motion). Contrary to other implementations such as capsules, heat, water, and mechanical forces, green light even with low intensity has potential to provide fast (less than 3 min) and repetitive recovery of a damaged electrical conductor without any direct invasion. Also, the multiple, irregular cracks resulting from vigorous motions of wearable devices can be simultaneously recovered regardless of the light incident angles and crack propagation directions, thus, making light‐powered healing more accessible to wearable devices beyond existing system options. To develop and demonstrate the key concepts of this system, combined studies on materials, integrations, and light‐powering strategy for recovering a damaged wearable electrical conductor are systematically carried out in the present work. Light‐powered delivery of silver nanowires can offer a rapid, noninvasive, repetitive, and on‐demand healing of a wearable electrical conductor. To develop the concept, combined studies on materials, integrations, and light‐powering strategy for recovering a damaged wearable electrical conductor are carried out in the present work.
      PubDate: 2014-09-15T06:57:25.812263-05:
      DOI: 10.1002/adfm.201401666
  • Low‐Noise Multispectral Photodetectors Made from All
           Solution‐Processed Inorganic Semiconductors
    • Authors: Jesse R. Manders; Tzung‐Han Lai, Yanbin An, Weikai Xu, Jaewoong Lee, Do Young Kim, Gijs Bosman, Franky So
      Pages: n/a - n/a
      Abstract: Infrared, visible, and multispectral photodetectors are important components for sensing, security and electronics applications. Current fabrication of these devices is based on inorganic materials grown by epitaxial techniques which are not compatible with low‐cost large‐scale processing. Here, air‐stable multispectral solution‐processed inorganic double heterostructure photodetectors, using PbS quantum dots (QDs) as the photoactive layer, colloidal ZnO nanoparticles as the electron transport/hole blocking layer (ETL/HBL), and solution‐derived NiO as the hole transport/electron blocking layer (HTL/EBL) are reported. The resulting device has low dark current density of 20 nA cm‐2 with a noise equivalent power (NEP) on the order of tens of picowatts across the detection spectra and a specific detectivity (D*) value of 1.2 × 1012 cm Hz1/2 W‐1. These parameters are comparable to commercially available Si, Ge, and InGaAs photodetectors. The devices have a linear dynamic range (LDR) over 65 dB and a bandwidth over 35 kHz, which are sufficient for imaging applications. Finally, these solution‐processed inorganic devices have a long storage lifetime in air, even without encapsulation. Air‐stable, all‐solution processed all‐inorganic multispectral photodetectors using PbS quantum dots as the photoactive layer, colloidal ZnO nanoparticles as the electron transport/hole blocking layer, and solution‐derived NiO as the hole transport/electron blocking layer are reported. The resulting devices have very low dark current density with a noise equivalent power on the order of tens of picowatts across the detection spectra. The performance parameters are comparable to commercially available Si, Ge, and InGaAs photodetectors and the device has a long unencapsulated storage lifetime in air.
      PubDate: 2014-09-15T06:57:22.038908-05:
      DOI: 10.1002/adfm.201402094
  • Nanograined Half‐Heusler Semiconductors as Advanced Thermoelectrics:
           An Ab Initio High‐Throughput Statistical Study
    • Authors: Jesús Carrete; Natalio Mingo, Shidong Wang, Stefano Curtarolo
      Pages: n/a - n/a
      Abstract: Nanostructuring has spurred a revival in the field of direct thermoelectric energy conversion. Nanograined materials can now be synthesized with higher figures of merit (ZT) than the bulk counterparts. This leads to increased conversion efficiencies. Despite considerable effort in optimizing the known and discovering the unknown, technology still relies upon a few limited solutions. Here ab initio modeling of ZT is performed for 75 nanograined compounds—the result of accurate distillation with electronic and thermodynamic filtering techniques from the 79 057 half‐Heusler entries available in the repository. For many of the compounds, the ZTs are markedly above those attainable with nanograined IV and III‐V semiconductors. About 15% of them may even outperform ZT ≈ 2 at high temperatures. This analysis elucidates the origin of the advantageous thermoelectric properties found within this broad material class. Machine learning techniques are used to unveil simple rules determining if a nanograined half‐Heusler compound is likely to be a good thermoelectric given its chemical composition. First‐principles calculations are used to model the thermoelectric properties of 75 nanograined compounds obtained after filtering through the 79 057 half‐Heusler entries available in the repository utilizing electronic and thermodynamic criteria. Many of the figures of merit obtained are markedly above those attainable with nanograined IV and III‐V semiconductors, and competitive with the state of the art.
      PubDate: 2014-09-15T06:57:12.617781-05:
      DOI: 10.1002/adfm.201401201
  • Modulating the Properties of Azulene‐Containing Polymers through
           Controlled Incorporation of Regioisomers
    • Authors: Kazuhiko Tsurui; Masahito Murai, Sung‐Yu Ku, Craig J. Hawker, Maxwell J. Robb
      Pages: n/a - n/a
      Abstract: Two libraries of random conjugated polymers are presented that incorporate varying ratios of regioisomeric azulene units connected via the 5‐membered or 7‐membered ring in combination with bithiophene or fluorene comonomers. It is demonstrated that the optoelectronic and stimuli‐responsive properties of the materials can be systematically modulated by tuning the relative percentage of each azulene building block in the polymer backbone. Significantly, these materials exhibit stimuli‐responsive behavior in the solid state with spin‐coated thin films undergoing rapid and reversible color switching. Ultimately, this work introduces a new design strategy in which the optoelectronic properties of conjugated polymers can be modulated by varying only the regiochemistry of the constituent building blocks along a polymer chain. Tuning the percentage of azulene regioisomers in conjugated polymers leads to systematic variation in optoelectronic properties. A new design strategy is demonstrated in which the properties of conjugated polymers can be modulated by simply varying the regiochemistry of the building blocks along the polymer chain. Significantly, these materials exhibit ­stimuli‐responsive behavior in the solid state with thin films undergoing rapid and reversible color switching.
      PubDate: 2014-09-12T10:02:21.137238-05:
      DOI: 10.1002/adfm.201402554
  • Biomineralization: Stress and Damage Mitigation from Oriented
           Nanostructures within the Radular Teeth of Cryptochiton stelleri (Adv.
           Funct. Mater. 39/2014)
    • Authors: Lessa Kay Grunenfelder; Enrique Escobar de Obaldia, Qianqian Wang, Dongsheng Li, Brian Weden, Christopher Salinas, Richard Wuhrer, Pablo Zavattieri, David Kisailus
      Pages: 6085 - 6085
      Abstract: The cover art depicts a row of ultrahard and abrasion‐resistant teeth from the giant chiton, Cryptochiton stelleri, grinding on a hard surface, which is a rendering of a cross‐section of the tooth itself. Chemical and ultrastructural features of the teeth, which enhance fracture mitigation are reported by D. Kisailus and team on page 6093. Lessons obtained from this work can be used towards the development of abrasion resistant materials.
      PubDate: 2014-10-15T12:40:32.100857-05:
      DOI: 10.1002/adfm.201470255
  • Flexible Electronics: Microflotronics: A Flexible, Transparent,
           Pressure‐Sensitive Microfluidic Film (Adv. Funct. Mater. 39/2014)
    • Authors: Ruya Li; Baoqing Nie, Philip Digiglio, Tingrui Pan
      Pages: 6086 - 6086
      Abstract: T. Pan and co‐workers present a flexible, transparent, and pressure‐sensitive microfluidic film, referred to as microflotronics, for large‐area dynamic pressure mapping. On page 6195, utilizing a continuous responsive microfluidic layer as the sensing element, the microflotronic sensors offer an alternative approach to the solid‐state counterparts, by offering an unprecedented sensitivity and ultrafast response time in a completely transparent, flexible, and adaptive package.
      PubDate: 2014-10-15T12:40:34.011017-05:
      DOI: 10.1002/adfm.201470256
  • Contents: (Adv. Funct. Mater. 39/2014)
    • Pages: 6087 - 6092
      PubDate: 2014-10-15T12:40:33.30147-05:0
      DOI: 10.1002/adfm.201470257
  • Stress and Damage Mitigation from Oriented Nanostructures within the
           Radular Teeth of Cryptochiton stelleri
    • Authors: Lessa Kay Grunenfelder; Enrique Escobar de Obaldia, Qianqian Wang, Dongsheng Li, Brian Weden, Christopher Salinas, Richard Wuhrer, Pablo Zavattieri, David Kisailus
      Pages: 6093 - 6104
      Abstract: Chiton are marine mollusks who use heavily mineralized and ultrahard teeth to feed on epilithic and endolithic algae on intertidal rocks. To fulfill this function, chiton teeth must be tough and wear‐resistant. Impressive mechanical properties are achieved in the chiton tooth through a hierarchically arranged composite structure consisting of a hard shell of organic‐encased and highly oriented nanostructured magnetite rods that surround a soft core of organic‐rich iron phosphate. Microscopic and spectroscopic analyses combined with finite element simulations are used to probe the ultrastructural features and uncover structure–mechanical property relationships in the fully mineralized teeth of the gumboot chiton Cryptochiton stelleri. By understanding the effects of the nanostructured architecture within the chiton tooth, abrasion‐resistant materials can be developed for tooling and machining applications, as well as coatings for equipment and medical implants. The teeth of the chiton are hard and abrasion resistant. Local and global chemical and ultrastructural features of the teeth, as well as chemical and structural gradients which enhance fracture mitigation, are reported. Lessons obtained can be used towards the development of abrasion resistant materials for tooling and machining applications, as well as coatings for equipment and medical implants.
      PubDate: 2014-08-11T14:08:40.41293-05:0
      DOI: 10.1002/adfm.201401091
  • Hierarchical Free‐Standing Carbon‐Nanotube Paper Electrodes
           with Ultrahigh Sulfur‐Loading for Lithium–Sulfur Batteries
    • Authors: Zhe Yuan; Hong‐Jie Peng, Jia‐Qi Huang, Xin‐Yan Liu, Dai‐Wei Wang, Xin‐Bing Cheng, Qiang Zhang
      Pages: 6105 - 6112
      Abstract: The rational combination of conductive nanocarbon with sulfur leads to the formation of composite cathodes that can take full advantage of each building block; this is an effective way to construct cathode materials for lithium–sulfur (Li–S) batteries with high energy density. Generally, the areal sulfur‐loading amount is less than 2.0 mg cm−2, resulting in a low areal capacity far below the acceptable value for practical applications. In this contribution, a hierarchical free‐standing carbon nanotube (CNT)‐S paper electrode with an ultrahigh sulfur‐loading of 6.3 mg cm−2 is fabricated using a facile bottom–up strategy. In the CNT–S paper electrode, short multi‐walled CNTs are employed as the short‐range electrical conductive framework for sulfur accommodation, while the super‐long CNTs serve as both the long‐range conductive network and the intercrossed mechanical scaffold. An initial discharge capacity of 6.2 mA·h cm−2 (995 mA·h g−1), a 60% utilization of sulfur, and a slow cyclic fading rate of 0.20%/cycle within the initial 150 cycles at a low current density of 0.05 C are achieved. The areal capacity can be further increased to 15.1 mA·h cm−2 by stacking three CNT–S paper electrodes—resulting in an areal sulfur‐loading of 17.3 mg cm−2—for the cathode of a Li–S cell. The as‐obtained free‐standing paper electrode are of low cost and provide high energy density, making them promising for flexible electronic devices based on Li–S batteries. A hierarchical free‐standing paper electrode is fabricated using short multi‐walled carbon nanotubes (MWCNTs) and super‐long CNTs. The MWCNTs function as a short‐range electrical conductive framework for sulfur accommodation, while super‐long CNTs act as both a long‐range conductive network and mechanical scaffold.
      PubDate: 2014-07-31T07:53:34.646949-05:
      DOI: 10.1002/adfm.201401501
  • Energy‐Efficient Growth: Multifunctional Three‐Dimensional
           T‐Junction Graphene Micro‐Wells: Energy‐Efficient,
           Plasma‐Enabled Growth and Instant Water‐Based Transfer for
           Flexible Device Applications (Adv. Funct. Mater. 39/2014)
    • Authors: Shailesh Kumar; Timothy van der Laan, Amanda Evelyn Rider, Lakshman Randeniya, Kostya (Ken) Ostrikov
      Pages: 6113 - 6113
      Abstract: A novel energy‐efficient plasma‐enabled approach for fabricating third generation 3D T‐junction graphene microwells and their instant chemical‐free water‐assisted decoupling and transfer process is reported by K. Ostrikov and co‐workers on page 6114. The structures deposited on a copper foil are then transferred without any significant damage, in de‐ionized or tap water at room temperature, into virtually any, including flexible transparent substrates, for their reliable and competitive optical and gas sensing applications.
      PubDate: 2014-10-15T12:40:29.939993-05:
      DOI: 10.1002/adfm.201470258
  • Multifunctional Three‐Dimensional T‐Junction Graphene
           Micro‐Wells: Energy‐Efficient, Plasma‐Enabled Growth and
           Instant Water‐Based Transfer for Flexible Device Applications
    • Authors: Shailesh Kumar; Timothy van der Laan, Amanda Evelyn Rider, Lakshman Randeniya, Kostya (Ken) Ostrikov
      Pages: 6114 - 6122
      Abstract: The “third‐generation” 3D graphene structures, T‐junction graphene micro‐wells (T‐GMWs) are produced on cheap polycrystalline Cu foils in a single‐step, low‐temperature (270 °C), energy‐efficient, and environment‐friendly dry plasma‐enabled process. T‐GMWs comprise vertical graphene (VG) petal‐like sheets that seemlessly integrate with each other and the underlying horizontal graphene sheets by forming T‐junctions. The microwells have the pico‐to‐femto‐liter storage capacity and precipitate compartmentalized PBS crystals. The T‐GMW films are transferred from the Cu substrates, without damage to the both, in de‐ionized or tap water, at room temperature, and without commonly used sacrificial materials or hazardous chemicals. The Cu substrates are then re‐used to produce similar‐quality T‐GMWs after a simple plasma conditioning. The isolated T‐GMW films are transferred to diverse substrates and devices and show remarkable recovery of their electrical, optical, and hazardous NO2 gas sensing properties upon repeated bending (down to 1 mm radius) and release of flexible trasparent display plastic substrates. The plasma‐enabled mechanism of T‐GMW isolation in water is proposed and supported by the Cu plasma surface modification analysis. Our GMWs are suitable for various optoelectronic, sesning, energy, and biomedical applications while the growth approach is potentially scalable for future pilot‐scale industrial production. Energy‐efficient plasma‐enabled chemical vapor deposition (CVD) synthesis is described, as well as a simple instant chemical‐free water‐assisted decoupling and a transfer process of unique three‐dimensional T‐junction graphene microwells structures. The structures deposited on a copper foil are then transferred without any significant damage, in de‐ionized or tap water at room temperature, into virtually any, including flexible transparent substrates, for their multifunctional device applications.
      PubDate: 2014-08-19T12:22:47.015608-05:
      DOI: 10.1002/adfm.201400992
  • Three‐Dimensional Structures of MoS2 Nanosheets with Ultrahigh
           Hydrogen Evolution Reaction in Water Reduction
    • Authors: Xiumei Geng; Wei Wu, Ning Li, Weiwei Sun, Johnathan Armstrong, Alaa Al‐hilo, Matthew Brozak, Jingbiao Cui, Tar‐pin Chen
      Pages: 6123 - 6129
      Abstract: The hydrogen evolution reaction in an alkaline environment using a non‐precious catalyst with much greater efficiency represents a critical challenge in research. Here, a robust and highly active system for hydrogen evolution reaction in alkaline solution is reported by developing MoS2 nanosheet arrays vertically aligned on graphene‐mediated 3D Ni networks. The catalytic activity of the 3D MoS2 nanostructures is found to increase by 2 orders of magnitude as compared to the Ni networks without MoS2. The MoS2 nanosheets vertically grow on the surface of graphene by employing tetrakis(diethylaminodithiocarbomato)molybdate(IV) as the molybdenum and sulfur source in a chemical vapor deposition process. The few‐layer MoS2 nanosheets on 3D graphene/nickel structure can maximize the exposure of their edge sites at the atomic scale and present a superior catalysis activity for hydrogen production. In addition, the backbone structure facilitates as an excellent electrode for charge transport. This precious‐metal‐free and highly efficient active system enables prospective opportunities for using alkaline solution in industrial applications. A robust and highly active system is demonstrated for the hydrogen evolution reaction in alkaline solution by developing MoS2 nanosheet arrays vertically aligned on graphene‐mediated 3D Ni networks. The catalytic activity of the 3D MoS2 nanostructures is found to increase by 2 orders of magnitude as compared to the Ni networks without MoS2.
      PubDate: 2014-07-28T13:05:26.247491-05:
      DOI: 10.1002/adfm.201401328
  • Improved CO2 Capture from Flue Gas by Basic Sites, Charge Gradients, and
           Missing Linker Defects on Nickel Face Cubic Centered MOFs
    • Authors: Elena López‐Maya; Carmen Montoro, Valentina Colombo, Elisa Barea, Jorge A. R. Navarro
      Pages: 6130 - 6135
      Abstract: The adsorptive properties of the isoreticular series [Ni8(OH)4(H2O)2(BDP_X)6] (H2BDP_X = 1,4‐bis(pyrazol‐4‐yl)benzene‐4‐X with X = H (1), OH (2), NH2 (3)) can be enhanced by postsynthetic treatment with an excess of KOH in ethanol. In the case of X = H, NH2, this treatment leads to partial removal of the organic linkers, deprotonation of coordinated water molecules and introduction of extraframework cations, giving rise to materials of K[Ni8(OH)5(EtO)‐(H2O)2(BDP_X)5.5] (1@KOH, 3@KOH) formulation, in which the original framework topology is maintained. By contrast, the same treatment with KOH in the [Ni8(OH)4(H2O)2(BDP_OH)6] (2) system, enclosing the more acidic phenol residues, leads to a new material containing a larger fraction of missing linker defects and extra‐framework cations as well as phenolate residues, giving rise to the material K3[Ni8(OH)3(EtO)(H2O)6(BDP_O)5] (2@KOH), which also conserves the original face cubic centered (fcu) topology. It is noteworthy that the introduction of missing linker defects leads to a higher accessible pore volume with a concomitant increased adsorption capacity. Moreover, the creation of coordinatively unsaturated metal centers, charge gradients, and phenolate nucleophilic sites in 2@KOH gives rise to a boosting of CO2 capture features with increased adsorption heat and adsorption capacity, as proven by the measurement of pulse gas chromatography and breakthrough curve measurements of simulated flue gas. A boosting of CO2 capture properties in a series of functional MOF materials can be achieved by post‐synthetic treatment with KOH ethanolic solutions, leading to linker removal and the concomitant creation of highly active surface sites for the adsorption of acidic gases.
      PubDate: 2014-07-30T01:57:38.774925-05:
      DOI: 10.1002/adfm.201400795
  • Layer‐by‐Layer Assembly of 3D Tissue Constructs with
           Functionalized Graphene
    • Authors: Su Ryon Shin; Behnaz Aghaei‐Ghareh‐Bolagh, Xiguang Gao, Mehdi Nikkhah, Sung Mi Jung, Alireza Dolatshahi‐Pirouz, Sang Bok Kim, Sun Min Kim, Mehmet R. Dokmeci, Xiaowu (Shirley) Tang, Ali Khademhosseini
      Pages: 6136 - 6144
      Abstract: Carbon‐based nanomaterials have been considered promising candidates to mimic certain structure and function of native extracellular matrix materials for tissue engineering. Significant progress has been made in fabricating carbon nanoparticle‐incorporated cell culture substrates, but only a limited number of studies have been reported on the development of 3D tissue constructs using these nanomaterials. Here, a novel approach to engineer 3D multilayer constructs using layer‐by‐layer (LbL) assembly of cells separated with self‐assembled graphene oxide (GO)‐based thin films is presented. The GO‐based structures are shown to serve as cell adhesive sheets that effectively facilitate the formation of multilayer cell constructs with interlayer connectivity. By controlling the amount of GO deposited in forming the thin films, the thickness of the multilayer tissue constructs could be tuned with high cell viability. Specifically, this approach could be useful for creating dense and tightly connected cardiac tissues through the co‐culture of cardiomyocytes and other cell types. In this work, the fabrication of stand‐alone multilayer cardiac tissues with strong spontaneous beating behavior and programmable pumping properties is demonstrated. Therefore, this LbL‐based cell construct fabrication approach, utilizing GO thin films formed directly on cell surfaces, has great potential in engineering 3D tissue structures with improved organization, electrophysiological function, and mechanical integrity. A multilayered cardiac tissue is fabricated by interfacing poly‐l‐lysine graphene oxide particles on the surface of each cell layer using a layer‐by‐layer technique. The particles embedded within the multilayer cardiac constructs improve cardiac cell organization, maturation, and cell–cell electrical coupling. Multilayer cardiac tissue shows strong spontaneous beating and frequency‐dependent opening/closing actuation under a low external electric field.
      PubDate: 2014-07-31T07:53:31.54928-05:0
      DOI: 10.1002/adfm.201401300
  • Aptamer‐Functionalized Multidimensional Conducting‐Polymer
           Nanoparticles for an Ultrasensitive and Selective
           Field‐Effect‐Transistor Endocrine‐Disruptor Sensors
    • Authors: Jun Seop Lee; Sung Gun Kim, Jaemoon Jun, Dong Hoon Shin, Jyongsik Jang
      Pages: 6145 - 6153
      Abstract: An endocrine disruptor (ED) is a type of xenobiotic compound that can cause serious diseases related to the estrous cycle, as well as various types of cancer. At low ED concentrations, estrogen receptors may respond as they would under physiological conditions. In this work, aptamer‐functionalized multidimensional conducting‐polymer (3‐carboxylate polypyrrole) nanoparticles (A_M_CPPyNPs) are fabricated for use in an FET sensor to detect bisphenol A (BPA). The multidimensional system, M_CPPyNPs, is first produced by means of dual‐nozzle electrospray of pristine CPPyNPs and vapor deposition polymerization of additional conducting polymer. The M_CPPyNPs are then immobilized on an amine‐functionalized (–NH2) interdigitated‐array electrode substrate, through the formation of covalent bonds with amide groups (–CONH). The amine‐functionalized BPA‐binding aptamer is then introduced in the same way as that for M_CPPyNP immobilization. The resulting A_M_CPPyNP‐based FET sensors exhibit ultrasensitivity and selectivity towards BPA at unprecedentedly low concentrations (1 fm) and among molecules with similar structures. Additionally, due to the covalent bonding involved in the immobilization processes, a longer lifetime is expected for the FET sensor. A multidimensional system comprising conjugated‐polymer nanoparticles, whose surfaces are decorated to increase surface area and allow further polymerization, is fabricated and functionalized with an aptamer. The resulting multidimensional nanoparticles are used in field‐effect transistors (FETs) that can act as sensors of the endocrine disruptor bisphenol A (BPA). The aptamer FET sensors exhibit ultrahigh sensitivity and selectivity toward BPA, and their lifetime is expected to exceed that of other FET biosensors.
      PubDate: 2014-07-31T07:53:37.622953-05:
      DOI: 10.1002/adfm.201401166
  • Fermi Level Pinning and Orbital Polarization Effects in Molecular
           Junctions: The Role of Metal Induced Gap States
    • Authors: Colin Van Dyck; Victor Geskin, Jérôme Cornil
      Pages: 6154 - 6165
      Abstract: Understanding the alignment of molecular orbitals and corresponding transmission peaks with respect to the Fermi level of the electrodes is a major challenge in the field of molecular electronics. In order to design functional devices, it is of utmost importance to assess whether controlled changes in the electronic structure of isolated compounds are preserved once they are inserted in the molecular junctions. Here, light is shed on this central issue by performing density functional theory calculations on junctions including diarylethene‐based molecules. It is demonstrated that the chemical potential equalization principle allows to rationalize the existence or not of a Fermi level pinning (i.e., same alignment in spite of a varying ionization potential in the isolated compounds), pointing to the essential role played by metal induced gap states (MIGS). It is further evidenced that the degree of level pinning is intimately linked to the degree of orbital polarization when a bias is applied between the two electrodes. The Fermi level alignment in molecular junctions can be either affected (S = 1) or unaffected (S = 0) by the modification of the ionization potential of the contacted molecule. Here, it is shown that a transition between these two behaviors is achievable by a simple substitution, while the key role of metal induced gap states (MIGS) in the alignment and orbital polarization processes is further highlighted.
      PubDate: 2014-08-05T10:25:28.005988-05:
      DOI: 10.1002/adfm.201400809
  • Helicity Control of π‐Stacked Assemblies of
           Oligo(para‐phenylene) Derivatives Using Photoresponsive Chiral
           Moieties at Terminal Sites
    • Authors: Benedict A. San Jose; Tomoki Ashibe, Naoki Tada, Shinichi Yorozuya, Kazuo Akagi
      Pages: 6166 - 6171
      Abstract: Oligo(para‐phenylene) (OPP) derivatives bearing photoresponsive chiral dithienylethene (DE*) terminal moieties that induce chirality in the OPP main chain are synthesized. In the assembled state, the photoisomerization of the chiral DE* terminal moieties prior to assembly, from the open to the closed form, leads to a change in the helicity of the π‐stacked structures. The circular dichroism spectra of mixed solvent solutions and cast films of the OPP assemblies exhibit bisignate Cotton effects in the absorption region associated with the oligomer main chain: these features indicate the presence of helically π‐stacked structures. Furthermore, the chiral transcription of racemic poly(bithiophenethiophene) (PBTT) by chiral OPP in the assembled state is demonstrated. The chirally transcribed PBTT shows a change in helicity upon the photoisomerization of the chiral DE* terminal moieties of OPP. To the best of our knowledge, this is the first report of helicity control of a helically π‐stacked conjugated oligomer through the photoisomerization of a chiral photoresponsive moiety. Such assemblies could be attractive for use in optoelectronic devices and optical memory systems. Oligo(para‐phenylene) (OPP) derivatives bearing photoresponsive chiral dithienyl­ethene (DE*) terminal moieties are synthesized. Photoisomerization of the chiral DE* terminal moieties prior to assembly, from the open to closed form, changes the handedness of the helically π‐stacked structures in the assembled state. Furthermore, the chiral transcription of racemic poly(bithiophenethiophene) by the assembled chiral OPP is demonstrated.
      PubDate: 2014-08-08T00:24:00.772554-05:
      DOI: 10.1002/adfm.201401453
  • Measuring Reduced C60 Diffusion in Crosslinked Polymer Films by Optical
    • Authors: Florian Fischer; Tobias Hahn, Heinz Bässler, Irene Bauer, Peter Strohriegl, Anna Köhler
      Pages: 6172 - 6177
      Abstract: The diffusion of fullerenes such as C60 and PCBM in organic semiconductors is a key factor in controlling the efficiency of organic solar cells, though it is challenging to measure and to control. A simple optical method based on photoluminescence quenching is developed to assess the diffusion of a quencher molecule such as C60 through a semiconducting polymer film, in this case made with the polymer polyfluorene. When the mobility of the polymer chains is reduced by chemical crosslinking, the diffusion coefficient of C60 can be reduced by up to three orders of magnitude. The diffusion of fullerenes such as C60 and PCBM in organic semiconductors can be measured using a novel simple optical method based on photoluminescence quenching. When the mobility of the polymer chains is reduced by chemical crosslinking, the diffusion coefficient of C60 can be reduced by up to three orders of magnitude.
      PubDate: 2014-08-08T11:09:38.538179-05:
      DOI: 10.1002/adfm.201401153
  • Highly Efficient TADF OLEDs: How the Emitter–Host Interaction
           Controls Both the Excited State Species and Electrical Properties of the
           Devices to Achieve Near 100% Triplet Harvesting and High Efficiency
    • Authors: Vygintas Jankus; Przemyslaw Data, David Graves, Callum McGuinness, Jose Santos, Martin R. Bryce, Fernando B. Dias, Andrew P. Monkman
      Pages: 6178 - 6186
      Abstract: New emitters that can harvest both singlet and triplet excited states to give 100% internal conversion of charge into light, are required to replace Ir based phosphors in organic light emitting diodes (OLEDs). Molecules that have a charge transfer (CT) excited state can potentially achieve this through the mechanism of thermally activated delayed fluorescence (TADF). Here, it is shown that a D–A charge transfer molecule in the solid state, can emit not only via an intramolecular charge transfer (ICT) excited state, but also from exciplex states, formed between the molecule and the host material. OLEDs based on a previously studied D–A–D molecule in a host TAPC achieves >14% external electroluminescence yield and shows nearly 100% efficient triplet harvesting. In these devices, it is unambiguously established that the triplet states are harvested via TADF, but more interestingly, these results are found to be independent of whether the emitter is the ICT state or the D–A–D/host exciplex. New emitters harvesting triplets to give 100% internal efficiency are required to replace Ir based phosphors in OLEDs. Here, it is shown that a D–A molecule in the solid state emits via an intramolecular charge transfer excited state and via exciplex states, and OLEDs based on thermally activated delayed fluorescence achieve >14% external electroluminescence yield and 100% efficient triplet harvesting.
      PubDate: 2014-08-08T11:09:41.362334-05:
      DOI: 10.1002/adfm.201400948
  • Intracellularly Degradable Hydrogen‐Bonded Polymer Capsules
    • Authors: Kristian Kempe; Sher Leen Ng, Sylvia T. Gunawan, Ka Fung Noi, Frank Caruso
      Pages: 6187 - 6194
      Abstract: The assembly of low‐fouling polymer capsules with redox‐responsive behavior and intracellular degradability is reported. Thiol‐containing poly(2‐ethyl‐2‐oxazoline) (PEtOxMASH) brushes are synthesized by atom transfer radical polymerization (ATRP) of oligo(2‐ethyl‐2‐oxazoline)methacrylate and glycidyl methacrylate (GMA) and subsequent ring‐opening reaction of the GMA. Sequential deposition of PEtOxMASH/poly(methacrylic acid) (PMA) multilayers onto silica (SiO2) particle templates and crosslinking through disulfide formation yield stable capsules after the removal of the SiO2 templates by buffered hydrofluoric acid (HF). The redox‐responsive nature of the disulfide crosslinking groups enables the degradation of these capsules under simulated intracellular conditions at pH 5.9 and 5 mm glutathione (GSH). Furthermore, capsule degradation is observed after incubation with dendritic (JAWS II) cells. Even at high capsule‐to‐cell ratios, PEtOxMASH capsules show only negligible cytotoxicity. Quartz crystal microgravimetry (QCM) studies, using 100% human serum, reveal that films prepared from PEtOxMASH exhibit low‐fouling properties. The degradation and low‐fouling properties are promising for application of PEtOxMASH films/capsules for the delivery and triggered release of therapeutics. Low‐fouling, redox‐responsive polymer capsules based on functional poly(2‐oxazoline)s are assembled. These capsules are shown to degrade under simulated intracellular conditions as well as intracellularly. Their low‐fouling properties make them promising for the delivery and triggered release of therapeutics.
      PubDate: 2014-08-13T14:31:10.563704-05:
      DOI: 10.1002/adfm.201401397
  • Microflotronics: A Flexible, Transparent, Pressure‐Sensitive
           Microfluidic Film
    • Authors: Ruya Li; Baoqing Nie, Philip Digiglio, Tingrui Pan
      Pages: 6195 - 6203
      Abstract: There is an increasing demand for sensitive, flexible, and low‐cost pressure sensing solutions for health monitoring, wearable sensing, robotic and prosthetic applications. Here, the first flexible and pressure‐sensitive microfluidic film is reported, referred to as a microflotronic, with high transparency and seamless integratability with the state‐of‐the‐art microelectronics. The microflotronic film represents the initial effort to utilize a continuous microfluidic layer as the sensing elements for large‐area dynamic pressure mapping applications, and meanwhile an ultrahigh sensitivity of 0.45 kPa−1 has been achieved in a compact, flexible, and transparent packaging. The response time of the device is in the millisecond range, which is at least an order of magnitude faster than that of its conventional flexible solid‐state counterparts. In addition, the fabrication process of the device is fully compatible with the industrial‐scale manufacturing of capacitive touchscreen devices and liquid‐crystal displays. The overall device packaging can be as thin as 200 μm with an optical transparency greater than 80%. Several practical applications were successfully demonstrated, including surface topology mapping and dynamic blood pressure monitoring. The microflotronic devices offer an alternative approach to the solid‐state pressure sensors, by offering an unprecedented sensitivity and ultrafast response time in a completely transparent, flexible and adaptive platform. A flexible, transparent, and pressure‐sensitive microfluidic film, referred to as a microflotronic, is reported for large‐area dynamic pressure mapping applications. Utilizing a continuous microfluidic layer as the sensing elements, the microflotronic devices offer an alternative approach to the solid‐state pressure sensors, by offering an unprecedented sensitivity and ultrafast response time in a completely transparent, flexible, and adaptive platform.
      PubDate: 2014-08-14T14:17:04.841805-05:
      DOI: 10.1002/adfm.201401527
  • Spontaneous Counterion‐Induced Vesicle Formation: Multivalent
           Binding to Europium(III) for a Wide‐Range Optical pH Sensor
    • Authors: Gaocan Li; Shiyong Zhang, Ningjie Wu, Yangyang Cheng, Jingsong You
      Pages: 6204 - 6209
      Abstract: A counterion‐directed molecular design strategy is described for the spontaneous formation of stable vesicles via readily available imidazolium salts with the EDTA counterion in aqueous media. The counteranion is employed to adjust the balance between hydrophobic and hydrophilic parts, which satisfies the requirement of packing parameter for vesicle formation. The counterion‐induced vesicles (CIVs) feature spontaneous formation, simple preparation, and easy availability of surfactants. Importantly, the unusual counterion‐induced vesicle‐like sphere aggregates can further chelate europium(III) ions to enhance the europium‐centered emission in aqueous media and make it viable for an optical pH sensor, which exhibits a linear response in a wide range of pH values from 3 to 11. To the best of our knowledge, this constitutes one of the widest ranges of Eu‐based pH sensors reported so far. This design concept has offered a new avenue for the preparation of functional vesicles. A counterion‐directed molecular design strategy for the spontaneous formation of stable vesicles via readily available imidazolium salts with the EDTA counteranion in aqueous media is proposed. Importantly, the unusual counterion‐induced vesicle‐like sphere aggregates can further chelate metal ions to enhance the europium‐centered emission in aqueous media and make it viable for an optical pH sensor.
      PubDate: 2014-07-29T07:56:05.841917-05:
      DOI: 10.1002/adfm.201400569
  • In Situ Study of Nanostructure and Electrical Resistance of Nanocluster
           Films Irradiated with Ion Beams
    • Authors: Weilin Jiang; Jennifer A. Sundararajan, Tamas Varga, Mark E. Bowden, You Qiang, John S. McCloy, Charles. H. Henager, Robert O. Montgomery
      Pages: 6210 - 6218
      Abstract: An in situ study is reported on the structural evolution in nanocluster films under He+ ion irradiation using an advanced helium ion microscope. The films consist of loosely interconnected nanoclusters of magnetite or iron‐magnetite (Fe‐Fe3O4) core‐shells. The nanostructure is observed to undergo dramatic changes under ion‐beam irradiation, featuring grain growth, phase transition, particle aggregation, and formation of nanowire‐like network and nanopores. Studies based on ion irradiation, thermal annealing and electron irradiation have indicated that the major structural evolution is activated by elastic nuclear collisions, while both electronic and thermal processes can play a significant role once the evolution starts. The electrical resistance of the Fe‐Fe3O4 films measured in situ exhibits a super‐exponential decay with dose. The behavior suggests that the nanocluster films possess an intrinsic merit for development of an advanced online monitor for fast neutron radiation with both high detection sensitivity and long‐term applicability, which can enhance safety measures in many nuclear operations. An in situ study on the nanostructural evolution and electrical resistance variation of Fe3O4 and Fe‐Fe3O4 core–shell nanocluster films under ion irradiation is presented. Grain growth, phase transition, particle aggregation, and formation of nanowire‐like network with nanopores are observed. The electrical resistance exhibits a super‐exponential decay with dose. This type of films may have potential as a sensing material for fast neutron monitoring.
      PubDate: 2014-08-11T14:58:23.456906-05:
      DOI: 10.1002/adfm.201400553
  • Reversible Switching of Liquid Crystalline Order Permits Synthesis of
           Homogeneous Populations of Dipolar Patchy Microparticles
    • Authors: Xiaoguang Wang; Daniel S. Miller, Juan J. de Pablo, Nicholas L. Abbott
      Pages: 6219 - 6226
      Abstract: The spontaneous positioning of colloids on the surfaces of micrometer‐sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, herein it is demonstrated that adsorbate‐driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface‐driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus‐like” microparticles. By using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field. Switching of the internal configurations of micrometer‐sized droplets of liquid crystal is used to uniformly position colloids on their surfaces, thus enabling formation of homogeneous populations of patchy microdroplets. The method is generalizable and, when combined with photo‐polymerization of the droplets, can be utilized for synthesis of solid “Janus‐like” microparticles or functional patchy microparticles with dipolar symmetry, including magnetically responsive systems.
      PubDate: 2014-08-15T03:05:29.849767-05:
      DOI: 10.1002/adfm.201400911
  • Pressure Sensitive Adhesion of an Elastomeric Protein Complex Extracted
           From Squid Ring Teeth
    • Authors: Abdon Pena‐Francesch; Bulent Akgun, Ali Miserez, Wenpeng Zhu, Huajian Gao, Melik C. Demirel
      Pages: 6227 - 6233
      Abstract: The pressure sensitive adhesion characteristic of a protein complex extracted from squid ring teeth (SRT), which exhibits an unusual and reversible transition from a solid to a melt, is studied. The native SRT is an elastomeric protein complex that has standard amino acids, and it does not function as adhesives in nature. The SRT can be thermally shaped into any 3D geometry (e.g., thin films, ribbons, colloids), and it has a glass transition temperature of 32 °C in water. Underwater adhesion strength of the protein film is approximately 1.5–2.5 MPa. The thermoplastic protein film could potentially be used in an array of fields, including dental resins, bandages for wound healing, and surgical sutures in the body. A protein‐based adhesives extracted from squid ring teeth is introduced. Underwater adhesion strength of the protein film is approximately 1.5–2.5 MPa. This reusable and recyclable bioelastomers could potentially have a wide range of applications in wet bioadhesive development including dental resins, bandages for wound healing, and surgical sutures in the body, all of which require wet adhesion.
      PubDate: 2014-08-11T14:58:38.271051-05:
      DOI: 10.1002/adfm.201401534
  • Light‐modulated TiOx Interlayer Dipole and Contact Activation in
           Organic Solar Cell Cathodes
    • Authors: Antonio Guerrero; Sylvain Chambon, Lionel Hirsch, Germà Garcia‐Belmonte
      Pages: 6234 - 6240
      Abstract: Understanding working mechanisms of selective interfacial layers and the underlying energetics of the organic semiconductor/electrode interface is an issue of primary concern for improving organic solar cell technologies. TiO x interlayers are used here to tune the selectivity of the cathode contact to electrons by controlled UV‐light activation. The S‐shaped kink observed for deactivated titania interlayers completely disappears after 2 min of UV‐light exposure yielding high fill factor (≈60%) and adequate efficiencies. UV‐light activation of complete cells alters the work function of the oxide that decreases about 650 mV as observed by Kelvin probe measurements. Capacitive techniques reveals a light‐intensity dependent shift in flat‐band voltage of up to 1.2 V under 1 sun illumination (without UV) in the case of deactivated TiO x interlayers. An increase in the magnitude of the light‐modulated dipole present at the oxide layer accounts for that voltage shift. Although the sign of the interface dipole would favor the extraction of electrons, the concomitant modification of the band bending in the organic semiconductor hinders an efficient extraction of carriers at positive voltages and originates the S‐shaped characteristics. After contact activation, the dipole strength does not change with the light intensity. Light‐modulated dipole (electron accumulation) present at TiO x interlayer accounts for the S‐shaped characteristics of organic solar cells. UV‐light activation tunes the selectivity of the cathode contact to electrons. Activated devices do not exhibit light‐dependent interface dipole. By using capacitance–voltage measurements a complete picture of the contact energetics is drawn.
      PubDate: 2014-08-14T14:15:20.344976-05:
      DOI: 10.1002/adfm.201401233
  • Electrodes: Hierarchical Free‐Standing Carbon‐Nanotube Paper
           Electrodes with Ultrahigh Sulfur‐Loading for Lithium–Sulfur
           Batteries (Adv. Funct. Mater. 39/2014)
    • Authors: Zhe Yuan; Hong‐Jie Peng, Jia‐Qi Huang, Xin‐Yan Liu, Dai‐Wei Wang, Xin‐Bing Cheng, Qiang Zhang
      Pages: 6244 - 6244
      Abstract: On page 6105, J.‐Q. Huang, Q. Zhang, and co‐workers discuss a hierarchical free‐standing carbon nanotube (CNT)/sulfur paper electrode with short CNTs as short‐range electrical conductive framework for sulfur accommodation and super long CNTs as both long‐range conductive networks and intercrossed mechanical scaffolds. Such rational design of flexible electrode offers the possibility to efficient use of active materials at practical loading.
      PubDate: 2014-10-15T12:40:39.275142-05:
      DOI: 10.1002/adfm.201470260
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