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CHEMISTRY (713 journals)                  1 2 3 4 | Last

Showing 1 - 200 of 735 Journals sorted alphabetically
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 29)
ACS Applied Polymer Materials     Hybrid Journal   (Followers: 9)
ACS Catalysis     Hybrid Journal   (Followers: 51)
ACS Chemical Neuroscience     Hybrid Journal   (Followers: 21)
ACS Combinatorial Science     Hybrid Journal   (Followers: 21)
ACS Macro Letters     Hybrid Journal   (Followers: 25)
ACS Materials Letters     Open Access   (Followers: 2)
ACS Medicinal Chemistry Letters     Hybrid Journal   (Followers: 43)
ACS Nano     Hybrid Journal   (Followers: 187)
ACS Photonics     Hybrid Journal   (Followers: 14)
ACS Symposium Series     Full-text available via subscription   (Followers: 3)
ACS Synthetic Biology     Hybrid Journal   (Followers: 28)
Acta Chemica Malaysia     Open Access  
Acta Chimica Slovaca     Open Access   (Followers: 2)
Acta Chimica Slovenica     Open Access   (Followers: 2)
Acta Chromatographica     Full-text available via subscription   (Followers: 7)
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 8)
Acta Scientifica Naturalis     Open Access   (Followers: 2)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 7)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 9)
Adsorption Science & Technology     Open Access   (Followers: 7)
Advanced Electronic Materials     Hybrid Journal   (Followers: 5)
Advanced Functional Materials     Hybrid Journal   (Followers: 70)
Advanced Journal of Chemistry, Section A     Open Access   (Followers: 3)
Advanced Journal of Chemistry, Section B     Open Access   (Followers: 1)
Advanced Science Focus     Free   (Followers: 5)
Advanced Theory and Simulations     Hybrid Journal   (Followers: 2)
Advanced Therapeutics     Hybrid Journal   (Followers: 1)
Advances in Chemical Engineering and Science     Open Access   (Followers: 104)
Advances in Chemical Science     Open Access   (Followers: 50)
Advances in Chemistry     Open Access   (Followers: 34)
Advances in Chemistry     Full-text available via subscription   (Followers: 4)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 16)
Advances in Environmental Chemistry     Open Access   (Followers: 9)
Advances in Enzyme Research     Open Access   (Followers: 10)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 31)
Advances in Nanoparticles     Open Access   (Followers: 17)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Polymer Science     Hybrid Journal   (Followers: 50)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 18)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Science and Technology     Full-text available via subscription   (Followers: 16)
Aerosol Science and Engineering     Hybrid Journal  
African Journal of Bacteriology Research     Open Access  
African Journal of Chemical Education     Open Access   (Followers: 5)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 6)
Aggregate     Open Access  
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Al-Kimia : Jurnal Penelitian Sains Kimia     Open Access  
Alchemy : Journal of Chemistry     Open Access   (Followers: 3)
Alchemy : Jurnal Penelitian Kimia     Open Access  
Alotrop     Open Access  
AMB Express     Open Access   (Followers: 1)
Ambix     Hybrid Journal   (Followers: 3)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 42)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 18)
American Journal of Chemistry     Open Access   (Followers: 37)
American Journal of Plant Physiology     Open Access   (Followers: 7)
Analyst     Hybrid Journal   (Followers: 36)
Analytical Science Advances     Open Access   (Followers: 1)
Angewandte Chemie     Hybrid Journal   (Followers: 152)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 223)
Annales Universitatis Mariae Curie-Sklodowska, sectio AA – Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 6)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 4)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 12)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 13)
Antiviral Chemistry and Chemotherapy     Open Access   (Followers: 1)
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 7)
Applied Spectroscopy     Full-text available via subscription   (Followers: 25)
Applied Surface Science     Hybrid Journal   (Followers: 30)
Arabian Journal of Chemistry     Open Access   (Followers: 4)
ARKIVOC     Open Access   (Followers: 1)
Asian Journal of Applied Chemistry Research     Open Access   (Followers: 1)
Asian Journal of Biochemistry     Open Access   (Followers: 2)
Asian Journal of Chemical Sciences     Open Access  
Asian Journal of Chemistry and Pharmaceutical Sciences     Open Access  
Asian Journal of Physical and Chemical Sciences     Open Access   (Followers: 2)
Atomization and Sprays     Full-text available via subscription   (Followers: 7)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 7)
Autophagy     Hybrid Journal   (Followers: 7)
Avances en Quimica     Open Access  
Biochemical Pharmacology     Hybrid Journal   (Followers: 11)
Biochemistry     Hybrid Journal   (Followers: 200)
Biochemistry Insights     Open Access   (Followers: 6)
Biochemistry Research International     Open Access   (Followers: 5)
BioChip Journal     Hybrid Journal  
Bioinorganic Chemistry and Applications     Open Access   (Followers: 5)
Biointerface Research in Applied Chemistry     Open Access  
Biointerphases     Open Access   (Followers: 1)
Biology, Medicine, & Natural Product Chemistry     Open Access   (Followers: 2)
Biomacromolecules     Hybrid Journal   (Followers: 22)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 10)
Biomedical Chromatography     Hybrid Journal   (Followers: 6)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 3)
BioNanoScience     Partially Free   (Followers: 3)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 93)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 66)
Bioorganic Chemistry     Hybrid Journal   (Followers: 9)
Biopolymers     Hybrid Journal   (Followers: 15)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Bitácora Digital     Open Access  
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of Institute of Chemistry and Chemical Technology, Mongolian Academy of Sciences     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: 24)
Bulletin of the Korean Chemical Society     Hybrid Journal   (Followers: 1)
Cakra Kimia (Indonesian E-Journal of Applied Chemistry)     Open Access  
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 1)
Canadian Journal of Chemistry     Hybrid Journal   (Followers: 12)
Canadian Mineralogist     Full-text available via subscription   (Followers: 5)
Carbohydrate Polymer Technologies and Applications     Open Access  
Carbohydrate Polymers     Hybrid Journal   (Followers: 8)
Carbohydrate Research     Hybrid Journal   (Followers: 24)
Carbon     Hybrid Journal   (Followers: 65)
Carbon Capture Science & Technology     Open Access   (Followers: 4)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 9)
Catalysis Science and Technology     Hybrid Journal   (Followers: 9)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 4)
Cell Reports Physical Science     Open Access  
Cellulose     Hybrid Journal   (Followers: 8)
Cereal Chemistry     Full-text available via subscription   (Followers: 4)
Chem     Hybrid Journal   (Followers: 6)
Chem Catalysis     Hybrid Journal   (Followers: 5)
ChemBioEng Reviews     Full-text available via subscription   (Followers: 3)
ChemCatChem     Hybrid Journal   (Followers: 8)
Chemical and Engineering News     Free   (Followers: 21)
Chemical Bulletin of Kazakh National University     Open Access  
Chemical Communications     Hybrid Journal   (Followers: 80)
Chemical Engineering Research and Design     Hybrid Journal   (Followers: 25)
Chemical Physics Impact     Full-text available via subscription   (Followers: 4)
Chemical Research in Chinese Universities     Hybrid Journal   (Followers: 4)
Chemical Research in Toxicology     Hybrid Journal   (Followers: 22)
Chemical Reviews     Hybrid Journal   (Followers: 173)
Chemical Science     Open Access   (Followers: 39)
Chemical Science International Journal     Open Access  
Chemical Technology     Open Access   (Followers: 74)
Chemical Thermodynamics and Thermal Analysis     Open Access   (Followers: 6)
Chemical Vapor Deposition     Hybrid Journal   (Followers: 4)
Chemie in Unserer Zeit     Hybrid Journal   (Followers: 54)
Chemie-Ingenieur-Technik (Cit)     Hybrid Journal   (Followers: 21)
ChemInform     Hybrid Journal   (Followers: 5)
Chemistry & Biodiversity     Hybrid Journal   (Followers: 7)
Chemistry & Industry     Full-text available via subscription   (Followers: 6)
Chemistry - A European Journal     Hybrid Journal   (Followers: 123)
Chemistry - An Asian Journal     Hybrid Journal   (Followers: 19)
Chemistry Africa : A Journal of the Tunisian Chemical Society     Hybrid Journal  
Chemistry and Materials Research     Open Access   (Followers: 17)
Chemistry Central Journal     Open Access   (Followers: 4)
Chemistry Education Research and Practice     Free   (Followers: 6)
Chemistry Education Review     Open Access   (Followers: 1)
Chemistry in Education     Open Access   (Followers: 3)
Chemistry Letters     Full-text available via subscription   (Followers: 44)
Chemistry of Heterocyclic Compounds     Hybrid Journal   (Followers: 5)
Chemistry of Materials     Hybrid Journal   (Followers: 158)
Chemistry of Natural Compounds     Hybrid Journal   (Followers: 10)
Chemistry World     Hybrid Journal   (Followers: 20)
Chemistry-Didactics-Ecology-Metrology     Open Access  
ChemistryOpen     Open Access   (Followers: 1)
ChemistrySelect     Hybrid Journal   (Followers: 1)
Chemistry–Methods     Open Access   (Followers: 1)
Chemkon - Chemie Konkret, Forum Fuer Unterricht Und Didaktik     Hybrid Journal  
ChemNanoMat     Hybrid Journal   (Followers: 1)
Chemoecology     Hybrid Journal   (Followers: 2)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 13)
ChemPhotoChem     Hybrid Journal  
ChemPhysChem     Hybrid Journal   (Followers: 12)
ChemPhysMater     Full-text available via subscription   (Followers: 5)
ChemPlusChem     Hybrid Journal   (Followers: 2)
Chempublish Journal     Open Access  
ChemSystemsChem     Hybrid Journal   (Followers: 1)
ChemTexts     Hybrid Journal   (Followers: 1)
CHIMIA International Journal for Chemistry     Open Access   (Followers: 2)
Chinese Journal of Chemistry     Hybrid Journal   (Followers: 6)
Chinese Journal of Polymer Science     Hybrid Journal   (Followers: 9)
Chromatographia     Hybrid Journal   (Followers: 22)
Chromatography Research International     Open Access   (Followers: 4)
Ciencia     Open Access  
Clay Minerals     Hybrid Journal   (Followers: 7)
Cogent Chemistry     Open Access   (Followers: 3)
Colloid and Interface Science Communications     Open Access  
Colloid and Polymer Science     Hybrid Journal   (Followers: 6)
Colloids and Surfaces B: Biointerfaces     Hybrid Journal   (Followers: 8)
Combinatorial Chemistry & High Throughput Screening     Hybrid Journal   (Followers: 2)
Combustion Science and Technology     Hybrid Journal   (Followers: 26)
Comments on Inorganic Chemistry: A Journal of Critical Discussion of the Current Literature     Hybrid Journal   (Followers: 1)
Communications Chemistry     Open Access   (Followers: 2)
Communications Materials     Open Access  
Composite Interfaces     Hybrid Journal   (Followers: 6)
Comptes Rendus : Chimie     Open Access  
Comptes Rendus : Physique     Open Access   (Followers: 2)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 11)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 13)
Computational Chemistry     Open Access   (Followers: 4)
Computers & Chemical Engineering     Hybrid Journal   (Followers: 11)
Coordination Chemistry Reviews     Full-text available via subscription   (Followers: 6)
Corrosion Communications     Open Access   (Followers: 4)
Critical Reviews in Biochemistry and Molecular Biology     Hybrid Journal   (Followers: 17)
Croatica Chemica Acta     Open Access  

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Colloids and Interfaces
Number of Followers: 0  

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ISSN (Online) 2504-5377
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  • Colloids and Interfaces, Vol. 6, Pages 1: Stable and Efficient
           Photoinduced Charge Transfer of MnFe2O4/Polyaniline Photoelectrode in
           Highly Acidic Solution

    • Authors: Mohammed Alsultan, Shaymaa Al-Rubaye, Amar Al-Keisy, Gerhard F. Swiegers, Intisar Ghanim Taha
      First page: 1
      Abstract: Tailoring conductive polymers with inorganic photocatalysts, which provide photoinduced electron-hole generation, have significantly enhanced composites leading to excellent photoelectrodes. In this work, MnFe2O4 nanoparticles prepared by a hydrothermal method were combined with polyaniline to prepare mixed (hybrid) slurries, which were cast onto flexible FTO to prepare photoelectrodes. The resulting photoelectrodes were characterized by XRD, FESEM, HRTEM and UV-VIS. The photoelectrochemical performance was investigated by linear sweep voltammetry and chronoamperometry. The photocurrent achieved by MnFe2O4/Polyaniline was 400 μA/cm2 at 0.8 V vs. Ag/AgCl in Na2SO4 (pH = 2) at 100 mW/cm2, while polyaniline alone achieved only 25 μA/cm2 under the same conditions. The best MnFe2O4/Polyaniline displayed an incident photon-to-current conversion efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) of 60% at 405 nm wavelength, and 0.17% at 0.8 V vs. Ag/AgCl, respectively. High and stable photoelectrochemical performance was achieved for more than 900 s in an acidic environment.
      Citation: Colloids and Interfaces
      PubDate: 2021-12-22
      DOI: 10.3390/colloids6010001
      Issue No: Vol. 6, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 43: The Effect of Substrate
           Temperature on the Evaporative Behaviour and Desiccation Patterns of
           Foetal Bovine Serum Drops

    • Authors: Marina Efstratiou, John Christy, Daniel Bonn, Khellil Sefiane
      First page: 43
      Abstract: The drying of bio-fluid drops results in the formation of complex patterns, which are morphologically and topographically affected by environmental conditions including temperature. We examine the effect of substrate temperatures between 20 °C and 40 °C, on the evaporative dynamics and dried deposits of foetal bovine serum (FBS) drops. The deposits consist of four zones: a peripheral protein ring, a zone of protein structures, a protein gel, and a central crystalline zone. We investigate the link between the evaporative behaviour, final deposit volume, and cracking. Drops dried at higher substrate temperatures in the range of 20 °C to 35 °C produce deposits of lower final volume. We attribute this to a lower water content and a more brittle gel in the deposits formed at higher temperatures. However, the average deposit volume is higher for drops dried at 40 °C compared to drops dried at 35 °C, indicating protein denaturation. Focusing on the protein ring, we show that the ring volume decreases with increasing temperature from 20 °C to 35 °C, whereas the number of cracks increases due to faster water evaporation. Interestingly, for deposits of drops dried at 40 °C, the ring volume increases, but the number of cracks also increases, suggesting an interplay between water evaporation and increasing strain in the deposits due to protein denaturation.
      Citation: Colloids and Interfaces
      PubDate: 2021-09-30
      DOI: 10.3390/colloids5040043
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 44: AFM Slip Length Measurements
           for Water at Selected Phyllosilicate Surfaces

    • Authors: Chen Zhang, Xuming Wang, Jiaqi Jin, Lixia Li, Jan D. Miller
      First page: 44
      Abstract: Most reported slip length measurements have been made at the surfaces of synthetic materials and modified synthetic materials. In contrast, few slip length measurements at the surface of unmodified natural mineral surfaces have been reported. In this regard, flow at the silica face surfaces of the phyllosilicate minerals, talc and mica, was considered. A slip boundary condition was expected at the nonpolar hydrophobic silica surface of talc leading to enhanced flow, and a no-slip boundary condition was expected at the hydrophilic silica surface of mica. Atomic force microscopy (AFM) slip length measurements were made at the talc and mica surfaces. The slip length results for the hydrophobic silica surface of talc were contrasted to the results for the hydrophilic silica surface of mica (no-slip flow). The results are discussed based on molecular dynamics simulations (MDS), as reported in the literature, and AFM images of surface nanobubbles. For nonpolar hydrophobic surfaces (such as talc), it is doubtful that the MDS interfacial water structure and the water exclusion zone (3.2 Å) account for the AFM slip flow with slip lengths as great as 95 nm. Rather, a better explanation for the AFM slip flow condition is based on reduced interfacial viscosity due to the presence of dissolved gas and the accommodation of pancake nanobubbles at the talc surface having a height dimension of magnitude similar to the slip length.
      Citation: Colloids and Interfaces
      PubDate: 2021-10-01
      DOI: 10.3390/colloids5040044
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 45: Electrophoretic Mobility and
           Electric Conductivity of Salt-Free Suspensions of Charged Soft Particles

    • Authors: Wei C. Lin, Huan J. Keh
      First page: 45
      Abstract: A unit cell model is employed to analyze the electrophoresis and electric conduction in a concentrated suspension of spherical charged soft particles (each is a hard core coated with a porous polyelectrolyte layer) in a salt-free medium. The linearized Poisson–Boltzmann equation applicable to a unit cell is solved for the equilibrium electrostatic potential distribution in the liquid solution containing the counterions only surrounding a soft particle. The counterionic continuity equation and modified Stokes/Brinkman equations are solved for the ionic electrochemical potential energy and fluid velocity distributions, respectively. Closed-form formulas for the electrophoretic mobility of the soft particles and effective electric conductivity of the suspension are derived, and the effect of particle interactions on these transport characteristics is interesting and significant. Same as the case in a suspension containing added electrolytes under the Debye–Hückel approximation, the scaled electrophoretic mobility in a salt-free suspension is an increasing function of the fixed charge density of the soft particles and decreases with increases in the core-to-particle radius ratio, ratio of the particle radius to the permeation length in the porous layer, and particle volume fraction, keeping the other parameters unchanged. The normalized effective electric conductivity of the salt-free suspension also increases with an increase in the fixed charge density and with a decrease in the core-to-particle radius ratio, but is not a monotonic function of the particle volume fraction.
      Citation: Colloids and Interfaces
      PubDate: 2021-10-17
      DOI: 10.3390/colloids5040045
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 46: On the Adequacy of Some
           Low-Order Moments Method to Simulate Certain Particle Removal Processes

    • Authors: Margaritis Kostoglou, Thodoris D. Karapantsios
      First page: 46
      Abstract: The population balance is an indispensable tool for studying colloidal, aerosol, and, in general, particulate systems. The need to incorporate spatial variation (imposed by flow) to it invokes the reduction of its complexity and degrees of freedom. It has been shown in the past that the method of moments and, in particular, the log-normal approximation can serve this purpose for certain phenomena and mechanisms. However, it is not adequate to treat gravitational deposition. In the present work, the ability of the particular method to treat diffusional and convective diffusional depositions relevant to colloid systems is studied in detail.
      Citation: Colloids and Interfaces
      PubDate: 2021-10-26
      DOI: 10.3390/colloids5040046
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 47: Electrochemical Perspective on
           Hematite–Malonate Interactions

    • Authors: Karolina Kędra, Marzena Łazarczyk, Tajana Begović, Danijel Namjesnik, Karolina Lament, Wojciech Piasecki, Piotr Zarzycki
      First page: 47
      Abstract: Organic matter (OM) interactions with minerals are essential in OM preservation against decomposition in the environment. Here, by combining potentiometric and electrophoretic measurements, we probed the mode of coordination and the role of pH-dependent electrostatic interactions between organic acids and an iron oxide surface. Specifically, we show that malonate ions adsorbed to a hematite surface in a wide pH window between 3 and 8.7 (point of zero charge). The mode of interactions varied with this pH range and depended on the acid and surface acidity constants. In the acidic environment, hematite surface potential was highly positive (+47 mV, pH 3). At pH < 4 malonate adsorption reduced the surface potential (+30 mV at pH 3) but had a negligible effect on the diffuse layer potential, consistent with the inner-sphere malonate complexation. Here, the specific and electrostatic interactions were responsible for the malonate partial dehydration and surface accumulation. These interactions weakened with an increasing pH and near PZC, the hematite surface charge was neutral on average. Adsorbed malonates started to desorb from the surface with less pronounced accumulation in the diffuse layer, which was reflected in zeta potential values. The transition between specific and non-specific sorption regimes was smooth, suggesting the coexistence of the inner- and outer-sphere complexes with a relative ratio that varied with pH.
      Citation: Colloids and Interfaces
      PubDate: 2021-10-31
      DOI: 10.3390/colloids5040047
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 48: Decarboxylation of p-Coumaric
           Acid during Pyrolysis on the Nanoceria Surface

    • Authors: Nataliia Nastasiienko, Tetiana Kulik, Borys Palianytsia, Mats Larsson, Tetiana Cherniavska, Mykola Kartel
      First page: 48
      Abstract: Temperature-programmed desorption mass spectrometry (TPD MS) was used to study the pyrolysis of p-coumaric acid (pCmA) on the nanoceria surface. The interaction of pCmA with the CeO2 surface was investigated by FT-IR spectroscopy. The obtained data indicated the formation on the nanoceria surface of bidentate carboxylate complexes with chelate (Δν = 62 cm−1) and bridge structure (Δν = 146 cm−1). The thermal decomposition of pCmA over nanoceria occurred in several stages, mainly by decarboxylation. The main decomposition product is 4-vinylphenol (m/z 120). The obtained data can be useful for studying the mechanisms of catalytic thermal transformations of lignin-containing raw materials using catalysts containing cerium oxide and the development of effective technologies for the isolation of pCmA from lignin.
      Citation: Colloids and Interfaces
      PubDate: 2021-11-11
      DOI: 10.3390/colloids5040048
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 49: Bacteria Cell Hydrophobicity
           and Interfacial Properties Relationships: A New MEOR Approach

    • Authors: Ehsan Ganji-Azad, Aliyar Javadi, Moein Jahanbani Veshareh, Shahab Ayatollahi, Reinhard Miller
      First page: 49
      Abstract: For microbial enhanced oil recovery (MEOR), different mechanisms have been introduced. In some of these papers, the phenomena and mechanisms related to biosurfactants produced by certain microorganisms were discussed, while others studied the direct impacts of the properties of microorganisms on the related mechanisms. However, there are only very few papers dealing with the direct impacts of microorganisms on interfacial properties. In the present work, the interfacial properties of three bacteria MJ02 (Bacillus Subtilis type), MJ03 (Pseudomonas Aeruginosa type), and RAG1 (Acinetobacter Calcoaceticus type) with the hydrophobicity factors 2, 34, and 79% were studied, along with their direct impact on the water/heptane interfacial tension (IFT), dilational interfacial visco-elasticity, and emulsion stability. A relationship between the adsorption dynamics and IFT reduction with the hydrophobicity of the bacteria cells is found. The cells with highest hydrophobicity (79%) exhibit a very fast dynamic of adsorption and lead to relatively large interfacial elasticity values at short adsorption time. The maximum elasticity values (at the studied frequencies) are observed for bacteria cells with the intermediate hydrophobicity factor (34%); however, at longer adsorption times. The emulsification studies show that among the three bacteria, just RAG1 provides a good capability to stabilize crude oil in brine emulsions, which correlates with the observed fast dynamics of adsorption and high elasticity values at short times. The salinity of the aqueous phase is also discussed as an important factor for the emulsion formation and stabilization.
      Citation: Colloids and Interfaces
      PubDate: 2021-11-19
      DOI: 10.3390/colloids5040049
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 50: Performance of Oleic Acid and
           Soybean Oil in the Preparation of Oil-in-Water Microemulsions for
           Encapsulating a Highly Hydrophobic Molecule

    • Authors: Laura Fernández-Peña, Boutaina Z. El Mojahid, Eduardo Guzmán, Francisco Ortega, Ramón G. Rubio
      First page: 50
      Abstract: This work analyzes the dispersion of a highly hydrophobic molecule, (9Z)-N-(1,3-dihydroxyoctadecan-2-yl)octadec-9-enamide (ceramide-like molecule), with cosmetic and pharmaceutical interest, by exploiting oil-in-water microemulsions. Two different oils, oleic acid and soybean oil, were tested as an oil phase while mixtures of laureth-5-carboxylic acid (Akypo) and 2-propanol were used for the stabilization of the dispersions. This allowed us to obtain stable aqueous-based formulations with a relatively reduced content of oily phase (around 3% w/w), that may enhance the bioavailability of this molecule by its solubilization in nanometric oil droplets (with a size range of 30–80 nm), that allow the incorporation of a ceramide-like molecule of up to 3% w/w, to remain stable for more than a year. The nanometric size of the droplet containing the active ingredient and the stability of the formulations provide the basis for evaluating the efficiency of microemulsions in preparing formulations to enhance the distribution and availability of ceramide-like molecules, helping to reach targets in cosmetic and pharmaceutical formulations.
      Citation: Colloids and Interfaces
      PubDate: 2021-11-22
      DOI: 10.3390/colloids5040050
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 51: Dense Phases of
           γ-Gliadins in Confined Geometries

    • Authors: Amélie Banc, Laurence Navailles, Jacques Leng, Denis Renard
      First page: 51
      Abstract: The binary phase diagram of γ-gliadin, a wheat storage protein, in water was explored thanks to the microevaporator, an original PDMS microfluidic device. This protein, usually qualified as insoluble in aqueous environments, displayed a partial solubility in water. Two liquid phases, a very dilute and a dense phase, were identified after a few hours of accumulation time in the microevaporator. This liquid–liquid phase separation (LLPS) was further characterized through in situ micro-Raman spectroscopy of the dilute and dense protein phases. Micro-Raman spectroscopy showed a specific orientation of phenylalanine residues perpendicular to the PDMS surfaces only for the diluted phase. This orientation was ascribed to the protein adsorption at interfaces, which would act as nuclei for the growth of dense phase in bulk. This study, thanks to the use of both aqueous solvent and a microevaporator, would provide some evidence for a possible physicochemical origin of the gliadin assembly in the endoplasmic reticulum of albumen cells, leading to the formation of dense phases called protein bodies. The microfluidic tool could be used also in food science to probe protein–protein interactions in order to build up phase diagrams.
      Citation: Colloids and Interfaces
      PubDate: 2021-11-23
      DOI: 10.3390/colloids5040051
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 52: Equilibrium, Kinetic, and
           Thermodynamic Studies of Cationic Dyes Adsorption on Corn Stalks Modified
           by Citric Acid

    • Authors: Liudmyla Soldatkina, Marianna Yanar
      First page: 52
      Abstract: The modification of agricultural wastes and their use as low-cost and efficient adsorbents is a prospective pathway that helps diminish waste and decrease environmental problems. In the present research, the natural adsorption capacity of corn stalks (CS) was improved by modification of their surface with citric acid. The adsorption capacity of the modified corn stalks (CS-C) was determined with the help of cationic dyes (methylene blue and malachite green). The equilibrium, kinetics, and thermodynamics of the cationic dyes on CS-C were studied. The Langmuir isotherm model best fitted the data both for methylene blue and malachite green adsorption on CS-C. The adsorption kinetics of the cationic dyes was well described by the pseudo-second order model. Thermodynamic studies revealed that adsorption of the cationic dyes on CS-C was an endothermic process. Negative results of ΔGo (between −31.8 and −26.3 kJ mol−1) indicated that the adsorption process was spontaneous in all the tested temperatures. The present study verified that citric acid-modified corn stalks can be used as a low-cost and effective adsorbent for removal of cationic dyes from aqueous solutions.
      Citation: Colloids and Interfaces
      PubDate: 2021-12-01
      DOI: 10.3390/colloids5040052
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 53: Prediction of Aqueous Solution
           Surface Tension of Some Surfactant Mixtures and Composition of Their
           Monolayers at the Solution—Air Interface

    • Authors: Bronisław Jańczuk, Anna Zdziennicka, Katarzyna Szymczyk, Maria Luisa González-Martín
      First page: 53
      Abstract: Measurements of the surface tension of the aqueous solution of SDDS mixture with fluorocarbon surfactants (FC) were carried out and considered in light of the surface tension of aqueous solutions of individual surfactants. Similar analyses were made for many other aqueous solutions of binary and ternary mixtures, taking into account the literature data of the surface tension of aqueous solutions of TX100, TX114, TX165, SDDS, SDS, CTAB, CPyB and FC. The possibility of predicting the surface tension of the aqueous solution of many surfactant mixtures from that of the mixture components using both the Szyszkowski, Fainerman and Miller and Joos concepts was analyzed. The surface tension of the aqueous solutions of surfactant mixtures was also considered based on the particular mixture component contribution to the water surface tension reduction. As a result, the composition of the mixed surface layer at the solution–air interface was discussed and compared to that which was determined using the Hua and Rosen concept. As follows from considerations, the surface tension of the aqueous solution of binary and ternary surfactant mixtures can be described and/or predicted.
      Citation: Colloids and Interfaces
      PubDate: 2021-12-17
      DOI: 10.3390/colloids5040053
      Issue No: Vol. 5, No. 4 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 35: Effect of Produced Sand
           Particles and Fines on Scale Inhibitor: A Review

    • Authors: Uche C. Anyanwu, Gbenga F. Oluyemi
      First page: 35
      Abstract: Application of scale inhibitors in oil and gas production is aimed at mitigating scale blockage during production. Many experimental, mathematical, and numerical simulation modeling works have been carried out to evaluate behavior, performance, and interaction of the scale inhibitor chemicals within porous media in relation to their efficiency in solving scale problem. However, the mechanisms underpinning scale inhibitors performance are not well published. Some research works have shown theoretically that not all scale inhibitors pumped into the formation adsorb onto the formation rock. Some of the inhibitors may adsorb on produced loose sand grains or colloidal fine sand particles which float and flow within the pore spaces along with the scale inhibitor mostly in unconsolidated reservoirs This paper provides a review of research work on the effect of produced loose sand or colloidal fine particles flow on polyphosphonates and polyphosphinopolymer scale inhibitors performances during crude production.
      Citation: Colloids and Interfaces
      PubDate: 2021-06-23
      DOI: 10.3390/colloids5030035
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 36: Electrohydrodynamic
           Instabilities in Free Emulsion Films

    • Authors: Farshid Mostowfi, Plamen Tchoukov, Nikolay Panchev, Tadeusz Dabros, Jan Czarnecki
      First page: 36
      Abstract: Electrohydrodynamic instabilities were induced in thin water-in-oil emulsion films by application of external DC electric field. The dominant wavelengths of instabilities were measured for constant electric fields of various strengths. The dominant wavelengths agreed reasonably well with theoretical predictions based on a linear stability model. The linear stability model used in this study took into account experimentally measured repulsive disjoining pressure and calculated Maxwell stress. The observation of such instabilities can help to understand the rupture mechanism of emulsion films under the influence of electric field.
      Citation: Colloids and Interfaces
      PubDate: 2021-07-01
      DOI: 10.3390/colloids5030036
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 37: A pH-Responsive Foam Formulated
           with PAA/Gemini 12-2-12 Complexes

    • Authors: Hernán Martinelli, Claudia Domínguez, Marcos Fernández Leyes, Sergio Moya, Hernán Ritacco
      First page: 37
      Abstract: In the search for responsive complexes with potential applications in the formulation of smart dispersed systems such as foams, we hypothesized that a pH-responsive system could be formulated with polyacrylic acid (PAA) mixed with a cationic surfactant, Gemini 12-2-12 (G12). We studied PAA-G12 complexes at liquid–air interfaces by equilibrium and dynamic surface tension, surface rheology, and X-ray reflectometry (XRR). We found that complexes adsorb at the interfaces synergistically, lowering the equilibrium surface tension at surfactant concentrations well below the critical micelle concentration (cmc) of the surfactant. We studied the stability of foams formulated with the complexes as a function of pH. The foams respond reversibly to pH changes: at pH 3.5, they are very stable; at pH > 6, the complexes do not form foams at all. The data presented here demonstrate that foam formation and its pH responsiveness are due to interfacial dynamics.
      Citation: Colloids and Interfaces
      PubDate: 2021-07-19
      DOI: 10.3390/colloids5030037
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 38: Ion-Specific and Solvent
           Effects on PDADMA–PSS Complexation and Multilayer Formation

    • Authors: Jasmina Jukić, Karla Korade, Ana-Marija Milisav, Ida Delač Marion, Davor Kovačević
      First page: 38
      Abstract: Among various parameters that influence the formation of polyelectrolyte complexes and multilayers, special emphasis should be placed on ion-specific and solvent effects. In our study, we systematically examined the above-mentioned effects on poly(diallyldimethylammonium chloride) (PDADMACl)-sodium poly(4-styrenesulfonate) (NaPSS) complexation in solution and at the surface by means of dynamic light scattering, ellipsometry and atomic force microscopy measurements. As solvents, we used water and water/ethanol mixture. The obtained results confirm the importance of ion-specific and solvent effects on complexes prepared in solution, as well as on multilayers built up on a silica surface. The experiments in mixed solvent solution showed that at a higher ethanol mole fraction, the decrease in monomer titrant to titrand ratio, at which the increase in the size of complexes is observed, takes place. The difference between chloride and bromide ions was more pronounced at a higher mole fraction of ethanol and in the case of positive complex formation, suggesting that the larger amount of bromide ions could be condensed to the polycation chain. These findings are in accordance with the results we obtained for polyelectrolyte multilayers and could be helpful for designing polyelectrolyte multilayers with tuned properties needed for various applications, primarily in the field of biomedicine.
      Citation: Colloids and Interfaces
      PubDate: 2021-07-21
      DOI: 10.3390/colloids5030038
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 39: A Multistate Adsorption Model
           for the Adsorption of C14EO4 and C14EO8 at the Solution/Air Interface

    • Authors: Valentin B. Fainerman, Volodymyr I. Kovalchuk, Eugene V. Aksenenko, Francesca Ravera, Libero Liggieri, Giuseppe Loglio, Alexander V. Makievski, Natalia O. Mishchuk, Emanuel Schneck, Reinhard Miller
      First page: 39
      Abstract: The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (CnEOm) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously surfactants that can adsorb in more than two possible conformations. The experimental data for C14EO4 and C14EO8 (dynamic and equilibrium surface tensions and surface dilational visco-elasticity as measured by bubble profile analysis tensiometry) are used to verify if a reorientation model with more than two possible adsorption states can better describe the complete set data of CnEOm adsorption layers at the water/air interface. The proposed refined theoretical model allows s different states of the adsorbing molecules at the interface. The comparison between the model and experiment demonstrates that, for C14EO4, the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C14EO8, a number of s = 10 adsorption states allows an optimum data description.
      Citation: Colloids and Interfaces
      PubDate: 2021-07-29
      DOI: 10.3390/colloids5030039
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 40: Effect of Surfactant Dynamics
           

    • Authors: Nina M. Kovalchuk, Mark J. H. Simmons
      First page: 40
      Abstract: Drops contained in an immiscible liquid phase are attractive as microreactors, enabling sound statistical analysis of reactions performed on ensembles of samples in a microfluidic device. Many applications have specific requirements for the values of local shear stress inside the drops and, thus, knowledge of the flow field is required. This is complicated in commonly used rectangular channels by the flow of the continuous phase in the corners, which also affects the flow inside the drops. In addition, a number of chemical species are present inside the drops, of which some may be surface-active. This work presents a novel experimental study of the flow fields of drops moving in a rectangular microfluidic channel when a surfactant is added to the dispersed phase. Four surfactants with different surface activities are used. Flow fields are measured using Ghost Particle Velocimetry, carried out at different channel depths to account for the 3-D flow structure. It is shown that the effect of the surfactant depends on the characteristic adsorption time. For fast-equilibrating surfactants with a characteristic time scale of adsorption that is much smaller than the characteristic time of surface deformation, this effect is related only to the decrease in interfacial tension, and can be accounted for by the change in capillary number. For slowly equilibrating surfactants, Marangoni stresses accelerate the corner flow, which changes the flow patterns inside the drop considerably.
      Citation: Colloids and Interfaces
      PubDate: 2021-08-02
      DOI: 10.3390/colloids5030040
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 41: Mathematical Modeling of
           Water-Soluble Astaxanthin Release from Binary Polysaccharide/Gelatin Blend
           Matrices

    • Authors: Katarzyna Łupina, Dariusz Kowalczyk, Tomasz Skrzypek, Barbara Baraniak
      First page: 41
      Abstract: Water-soluble AstaSana astaxanthin (AST) was loaded into 75/25 blend films made of polysaccharides (carboxymethyl cellulose (CMC), gum Arabic (GAR), starch sodium octenyl succinate (OSA), water-soluble soy polysaccharides (WSSP)) and gelatin (GEL) at levels of 0.25, 0.5, and 1%, respectively. Due to the presence of starch granules in the AST formulation, the supplemented films exhibited increased surface roughness as compared to the AST-free films. Apart from the CMC/GEL carrier, the migration of AST to water (25 °C, 32 h) was incomplete. Excluding the CMC-based carrier, the gradual rise in the AST concentration decreased the release rate. The Hopfenberg with time lag model provided the best fit for all release series data. Based on the quarter-release times (t25%), the 0.25% AST-supplemented OSA/GEL film (t25% = 13.34 h) ensured a 1.9, 2.2, and 148.2 slower release compared to the GAR-, WSSP- and CMC-based carriers, respectively. According to the Korsmeyer–Peppas model, the CMC-based films offered a quasi-Fickian release of AST (n < 0.5) with the burst effect (t100% = 0.5–1 h). In general, the release of AST from the other films was multi-mechanistic (n > 0.5), i.e., controlled at least by Fickian diffusion and the polymer relaxation (erosion) mechanism. The 1% AST-added WSSP/GEL system provided the most linear release profile.
      Citation: Colloids and Interfaces
      PubDate: 2021-08-03
      DOI: 10.3390/colloids5030041
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 42: The Oscillatory Spinning Drop
           Technique. An Innovative Method to Measure Dilational Interfacial
           Rheological Properties of Brine-Crude Oil Systems in the Presence of
           Asphaltenes

    • Authors: Ronald Marquez, Johnny Bullon, Ana Forgiarini, Jean-Louis Salager
      First page: 42
      Abstract: The oscillatory spinning drop method has been proven recently to be an accurate technique to measure dilational interfacial rheological properties. It is the only available equipment for measuring dilational moduli in low interfacial tension systems, as it is the case in applications dealing with surfactant-oil-water three-phase behavior like enhanced oil recovery, crude oil dehydration, or extreme microemulsion solubilization. Different systems can be studied, bubble-in-liquid, oil-in-water, microemulsion-in-water, oil-in-microemulsion, and systems with the presence of complex natural surfactants like asphaltene aggregates or particles. The technique allows studying the characteristics and properties of water/oil interfaces, particularly when the oil contains asphaltenes and when surfactants are present. In this work, we present a review of the measurements of crude oil-brine interfaces with the oscillating spinning drop technique. The review is divided into four sections. First, an introduction on the oscillating spinning drop technique, fundamental and applied concepts are presented. The three sections that follow are divided according to the complexity of the systems measured with the oscillating spinning drop, starting with simple surfactant-oil-water systems. Then the complexity increases, presenting interfacial rheology properties of crude oil-brine systems, and finally, more complex surfactant-crude oil-brine systems are reviewed. We have found that using the oscillating spinning drop method to measure interfacial rheology properties can help make precise measurements in a reasonable amount of time. This is of significance when systems with long equilibration times, e.g., asphaltene or high molecular weight surfactant-containing systems are measured, or with systems formulated with a demulsifier which is generally associated with low interfacial tension.
      Citation: Colloids and Interfaces
      PubDate: 2021-08-04
      DOI: 10.3390/colloids5030042
      Issue No: Vol. 5, No. 3 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 20: Conductive Nanofilms with
           Oppositely Charged Reduced Graphene Oxides as a Base for Electroactive
           Coatings and Sensors

    • Authors: Tomasz Kruk, Piotr Warszyński
      First page: 20
      Abstract: We demonstrate a method for the formation of multilayers composed of reduced graphene oxide (rGO), which can be used for transparent, conducting thin films. Using the layer-by-layer (LbL) assembly of positively and negatively charged GO sheets, we could obtain thin films with highly controllable sheet resistance. The natural negative charge of graphene oxide was turned to positive by the amidation reaction. After forming the multilayer films, the graphene oxide underwent thermal reduction at temperatures above 150 °C. The (rGO+/rGO−) films were characterized by UV-Vis and scanning electron microscopy (SEM), and their conductivity was measured by the four-point method. We found that after deposition of five (rGO+/rGO−), the coating structure reached the percolation limit, and the film resistance decreased more gradually to around 20 kΩ/sq for the films obtained by eleven deposition cycles with graphene oxide reduced at 250 °C. The formation of thin films on polyimide allows the forming of new flexible conductive materials, which can find applications, e.g., in biomedicine as new electroactive, low-cost, disposable sensors.
      Citation: Colloids and Interfaces
      PubDate: 2021-04-01
      DOI: 10.3390/colloids5020020
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 21: Influence of Hydrophilic
           Surfactants on the W1–W2 Coalescence in Double Emulsion Systems
           Investigated by Single Droplet Experiments

    • Authors: Nico Leister, Heike P. Karbstein
      First page: 21
      Abstract: Double emulsions are a promising formulation for encapsulation and targeted release in pharmaceutics, cosmetics and food. An inner water phase is dispersed in an oil phase, which is again emulsified in a second water phase. The encapsulated inner water phase can be released via diffusion or via coalescence, neither of which is desired during storage but might be intended during application. The two interfaces in a double emulsion are stabilized by a hydrophilic and a lipophilic surfactant, to prevent the coalescence of the outer and the inner emulsion, respectively. This study focuses on the influence of the hydrophilic surfactant on the release of inner water or actives encapsulated therein via coalescence of the inner water droplet with the outer O–W2 interface. Since coalescence and diffusion are difficult to distinguish in double emulsions, single-droplet experiments were used to quantify differences in the stability of inner droplets. Different lipophilic (PGPH and PEG-30 dipolyhydroxylstearate) and hydrophilic surfactants (ethoxylates, SDS and polymeric) were used and resulted in huge differences in stability. A drastic decrease in stability was found for some combinations, while other combinations resulted in inner droplets that could withstand coalescence longer. The destabilization effect of some hydrophilic surfactants depended on their concentration, but was still present at very low concentrations. A huge spread of the coalescence time for multiple determinations was observed for all formulations and the necessary statistical analysis is discussed in this work. The measured stabilities of single droplets are in good accordance with the stability of double emulsions for similar surfactant combinations found in literature. Therefore, single droplet experiments are suggested for a fast evaluation of potentially suitable surfactant combinations for future studies on double-emulsion stability.
      Citation: Colloids and Interfaces
      PubDate: 2021-04-08
      DOI: 10.3390/colloids5020021
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 22: Driven Transport of Dilute
           

    • Authors: Karthik Nagarajan, Shing Bor Chen
      First page: 22
      Abstract: Driven transport of dilute polymer solutions through porous media has been simulated using a recently proposed novel dissipative particle dynamics method satisfying the no-penetration and no-slip boundary conditions. The porous media is an array of overlapping spherical cavities arranged in a simple cubic lattice. Simulations were performed for linear, ring, and star polymers with 12 arms for two cases with the external force acting on (I) both polymer and solvent beads to model a pressure-driven flow; (II) polymer beads only, similar to electrophoresis. When the external force is in the direction of a principal axis, the extent of change in the polymers’ conformation and their alignment with the driving force is more significant for case I. These effects are most pronounced for linear chains, followed by rings and stars at the same molecular weight. Moreover, the polymer mean velocity is affected by its molecular weight and architecture as well as the direction and strength of the imposed force.
      Citation: Colloids and Interfaces
      PubDate: 2021-04-08
      DOI: 10.3390/colloids5020022
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 23: First Approach to Measure
           Interfacial Rheology at High-Pressure Conditions by the Oscillating Drop
           Technique

    • Authors: Albert Barrabino, Torleif Holt, Bård Bjørkvik, Erik Lindeberg
      First page: 23
      Abstract: An oscillating drop rheometer capable of operating under conditions of high pressure and high temperature has been built. The oscillating drop mechanism was able to support pressures as high as 1300 bar and successfully performed oscillations at constant pressure. Apparent elastic and viscous complex moduli were measured for a system of CO2 and synthetic seawater containing 100 ppm of a linear alkyl ethoxylate surfactant for different pressures and temperatures. The moduli had strong dependencies on both pressure and temperature. At temperatures of 40 and 80 °C, the apparent elastic modulus passed through a maximum for pressures between 100 and 300 bar. The harmonic distortion of the oscillations was calculated for all measurements, and it was found that drop oscillations below ca. 2.6 µL caused distortions above 10% due to a mechanical backlash of the motor.
      Citation: Colloids and Interfaces
      PubDate: 2021-04-13
      DOI: 10.3390/colloids5020023
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 24: Axisymmetric Slow Motion of a
           Porous Spherical Particle in a Viscous Fluid Using Time Fractional
           Navier–Stokes Equation

    • Authors: Jai Prakash, Chirala Satyanarayana
      First page: 24
      Abstract: In this paper, we present the unsteady translational motion of a porous spherical particle in an incompressible viscous fluid. In this case, the modified Navier–Stokes equation with fractional order time derivative is used for conservation of momentum external to the particle whereas modified Brinkman equation with fractional order time derivative is used internal to the particle to govern the fluid flow. Stress jump condition for the tangential stress along with continuity of normal stress and continuity of velocity vectors is used at the porous–liquid interface. The integral Laplace transform technique is employed to solve the governing equations in fluid and porous regions. Numerical inversion code in MATLAB is used to obtain the solution of the problem in the physical domain. Drag force experienced by the particle is obtained. The numerical results have been discussed with the aid of graphs for some specific flows, namely damping oscillation, sine oscillation and sudden motion. Our result shows a significant contribution of the jump coefficient and the fractional order parameter to the drag force.
      Citation: Colloids and Interfaces
      PubDate: 2021-04-13
      DOI: 10.3390/colloids5020024
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 25: Principles of Dispersing
           Powders for 3D Printing

    • Authors: Hongli Zhou, Xiaofeng Wang, Xinyu Wang, Chaoqun Peng, Richu Wang, Kechao Zhou
      First page: 25
      Abstract: During the past 30 years, more and more 3D-printing techniques based on suspensions with specific rheological properties have been innovated and improved. In this review, principles of dispersing and controlling powders for suspension-based 3D printing are summarized. The suspensions for direct ink writing (DIW) are taken as an example for 3D printing. According to the rheological property requirement of suspensions for direct ink writing, the routes on how its rheological properties can be manipulated are summarized and classified into two categories: I. self-solidification route; II. assistant-solidification route. The perspective on the future of 3D-printing techniques based on suspensions is also discussed.
      Citation: Colloids and Interfaces
      PubDate: 2021-04-14
      DOI: 10.3390/colloids5020025
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 26: Particle Deposition to Silica
           Surfaces Functionalized with Cationic Polyelectrolytes

    • Authors: Dominik Kosior, Plinio Maroni, Michal Borkovec
      First page: 26
      Abstract: Positively charged water-solid interfaces are prepared by adsorption of a cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) from aqueous solutions to planar silica substrates. These substrates are characterized by atomic force microscopy (AFM), optical reflectivity, and streaming current measurements. By tuning the amount of adsorbed polyelectrolyte, the surface charge of the substrate can be systematically varied. These substrates are further used to study deposition of sulfate latex nanoparticles, which is also accomplished by optical reflectivity. This deposition process is found to be consistent with an extension of the random sequential adsorption (RSA) model in a semi-quantitative fashion. Such deposition studies were further used to ascertain that the substrates obtained by in situ and ex situ functionalization behave in an identical fashion.
      Citation: Colloids and Interfaces
      PubDate: 2021-05-01
      DOI: 10.3390/colloids5020026
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 27: Formation of Myoglobin Corona
           at Polymer Microparticles

    • Authors: Zbigniew Adamczyk, Małgorzata Nattich-Rak
      First page: 27
      Abstract: Adsorption of myoglobin molecules at negatively charged polystyrene microparticles was studied using the dynamic light scattering (DLS), electrophoresis (LDV) and the solution depletion method involving atomic force microscopy (AFM). The measurements were carried out at pH 3.5 and NaCl concentration of 10−2 and 0.15 M. Initially, the stability of myoglobin solutions and the particle suspensions as a function of pH were determined. Afterward, the formation of myoglobin molecule corona was investigated via the direct electrophoretic mobility measurements, which were converted to the zeta potential. The experimental results were quantitatively interpreted in terms of the general electrokinetic model. This approach yielded the myoglobin corona coverage under in situ conditions. The maximum hard corona coverage was determined using the AFM concentration depletion method. It was equal to 0.9 mg m−2 for the NaCl concentration in the range 0.01 to 0.15 M and pH 3.5. The electrokinetic properties of the corona were investigated using the electrophoretic mobility measurements for a broad pH range. The obtained results confirmed that thorough physicochemical characteristics of myoglobin molecules can be acquired using nM amounts of the protein. It was also argued that this method can be used for performing electrokinetic characteristics of other proteins such as the SARS-Cov-2 spike protein exhibiting, analogously to myoglobin, a positive charge at acidic pHs.
      Citation: Colloids and Interfaces
      PubDate: 2021-05-06
      DOI: 10.3390/colloids5020027
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 28: UV Properties and Loading into
           Liposomes of Quinoline Derivatives

    • Authors: Sara Battista, Vincenzo Marsicano, Antonio Arcadi, Luciano Galantini, Massimiliano Aschi, Elena Allegritti, Alessandra Del Giudice, Luisa Giansanti
      First page: 28
      Abstract: The scientific relevance of quinolines is strictly linked to the fine-tuning of their features by functionalizing the heterocyclic core. Consequently, the compounds of this class are very versatile and can be used as possible drugs for a lot of medical applications. In this work, the inclusion of eight synthetic quinoline derivatives in liposomes formulated with different lipids was investigated in terms of the encapsulation efficiency and to highlight the effect on the liposome size distribution and thermotropic behavior. Excellent encapsulation was accomplished with all the quinoline/phospholipid combinations. Differences in the interactions at the molecular level, dependent on the quinoline molecular scaffolds and lipid structure, were observed, which could significantly bias the interaction with the drug and its release in pharmaceutical applications. Experiments in combination with computational studies demonstrated that the UV absorption of quinolines with expanded conjugation could be affected by the environment polarity. This was probably due to a solvent-dependent ability of these quinolines to stack into aggregates, which could also occur upon inclusion into the lipid bilayer.
      Citation: Colloids and Interfaces
      PubDate: 2021-05-07
      DOI: 10.3390/colloids5020028
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 29: Ordering and Dynamics of
           Interacting Colloidal Particles under Soft Confinement

    • Authors: Salvador Herrera-Velarde, Edith C. Euán-Díaz, Ramón Castañeda-Priego
      First page: 29
      Abstract: Confinement can induce substantial changes in the physical properties of macromolecules in suspension. Soft confinement is a particular class of restriction where the boundaries that constraint the particles in a region of the space are not well-defined. This scenario leads to a broader structural and dynamical behavior than observed in systems enclosed between rigid walls. In this contribution, we study the ordering and diffusive properties of a two-dimensional colloidal model system subjected to a one-dimensional parabolic trap. Increasing the trap strength makes it possible to go through weak to strong confinement, allowing a dimensional transition from two- to one-dimension. The non-monotonic response of the static and dynamical properties to the gradual dimensionality change affects the system phase behavior. We find that the particle dynamics are connected to the structural transitions induced by the parabolic trap. In particular, at low and intermediate confinement regimes, complex structural and dynamical scenarios arise, where the softness of the external potential induces melting and freezing, resulting in faster and slower particle diffusion, respectively. Besides, at strong confinements, colloids move basically along one direction, and the whole system behaves structurally and dynamically similar to a one-dimensional colloidal system.
      Citation: Colloids and Interfaces
      PubDate: 2021-05-17
      DOI: 10.3390/colloids5020029
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 30: Monolayers of Cholesterol and
           Cholesteryl Stearate at the Water/Vapor Interface: A Physico-Chemical
           Study of Components of the Meibum Layer

    • Authors: Ramón G. Rubio, Eduardo Guzmán, Francisco Ortega, Libero Liggieri
      First page: 30
      Abstract: Langmuir monolayers containing different amounts of cholesterol and cholesteryl stearate were studied at two different temperatures (24 °C and 35 °C). The main goal was to contribute towards the understanding of how the variations in the chemical composition may affect the physico-chemical properties of these specific lipid monolayers. The model mixture was chosen considering that cholesteryl esters are present in cell membranes and some other biological systems, including human tear lipids. Therefore, an investigation into the effect of the lipid monolayer composition on their interfacial properties may elucidate some of the fundamental reasons for the deficiencies in cell membranes and tear film functioning in vivo. The experimental results have shown that the molar ratio of the mixture plays a crucial role in the modulation of the Langmuir film properties. The condensing effects of the cholesterol and the interactions between the lipids in the monolayer were the main factors altering the monolayer response to dilatational deformation. The modification of the mixture compositions leads to significant changes in the Langmuir films and the mechanical performance, altering the ability of the monolayer to reduce the surface tension and the viscoelastic properties of the monolayers. This suggests that subtle modifications of the biomembrane composition may significantly alter its physiological function.
      Citation: Colloids and Interfaces
      PubDate: 2021-05-20
      DOI: 10.3390/colloids5020030
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 31: Understanding the Dynamics of a
           Lipid Monolayer on a Water Surface under a Marangoni Flow

    • Authors: Yohko F. Yano, Toshiaki Ina, Tomoya Uruga
      First page: 31
      Abstract: Biological membrane is composed of lipid molecules, because of its fluidity, it is possible to carry out physiological functions. Therefore, it is important to study the hydrodynamic properties of membranes toward understanding its function. Here, we observed the dynamical behavior of a lipid monolayer on the water surface under Marangoni flow. By using X-ray reflectometry, we obtained the tilt angle of the hydrocarbon chains of the lipid at different surface pressures. Comparing them with the dynamical surface pressure under Marangoni flow, it was found that the lipid molecules in rotational rather than translational motion. At low surface pressure, the molecular tilt angle is reduced by 20 degrees, even though the molecular area is reduced by at most 10%.
      Citation: Colloids and Interfaces
      PubDate: 2021-06-02
      DOI: 10.3390/colloids5020031
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 32: Special Issue in Honor of
           

    • Authors: Alexander Kamyshny, Victor M. Starov
      First page: 32
      Abstract: The majority of basic research that is conducted by Prof. Shlomo Magdassi in materials science [...] 
      Citation: Colloids and Interfaces
      PubDate: 2021-06-08
      DOI: 10.3390/colloids5020032
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 33: On Concept of Hybrid in Colloid
           Sciences

    • Authors: Camillo La Mesa, Gianfranco Risuleo
      First page: 33
      Abstract: The concepts hybrid and hybridization are common in many scientific fields, as in the taxonomic parts of botany and zoology, in modern genetic, and in the quantum–mechanical theory of atomic–molecular orbitals, which are of foremost relevance in most aspects of modern chemistry. Years later, scientists applied the concept hybrid to colloids, if the particles’ domains are endowed with functionalities differing each from the other in nature and/or composition. For such denomination to be fully valid, the domains belonging to a given hybrid must be recognizable each from another in terms of some intrinsic features. Thus, the concept applies to particles where a given domain has its own physical state, functionality, or composition. Literature examples in this regard are many. Different domains that are present in hybrid colloids self-organize, self-sustain, and self-help, according to the constraints dictated by kinetic and/or thermodynamic stability rules. Covalent, or non-covalent, bonds ensure the formation of such entities, retaining the properties of a given family, in addition to those of the other, and, sometimes, new ones. The real meaning of this behavior is the same as in zoology; mules are pertinent examples, since they retain some features of their own parents (i.e., horses and donkeys) but also exhibit completely new ones, such as the loss of fertility. In colloid sciences, the concept hybrid refers to composites with cores of a given chemical type and surfaces covered by moieties differing in nature, or physical state. This is the result of a mimicry resembling the ones met in a lot of biological systems and foods, too. Many combinations may occur. Silica nanoparticles on which polymers/biopolymers are surface-bound (irrespective of whether binding is covalent or not) are pertinent examples. Here, efforts are made to render clear the concept, which is at the basis of many applications in the biomedical field, and not only. After a historical background and on some features of the species taking part to the formation of hybrids, we report on selected cases met in modern formulations of mixed, and sometimes multifunctional, colloid entities.
      Citation: Colloids and Interfaces
      PubDate: 2021-06-09
      DOI: 10.3390/colloids5020033
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 34: Water and Ion Dynamics in
           Confined Media: A Multi-Scale Study of the Clay/Water Interface

    • Authors: Patrice Porion, Ali Asaad, Thomas Dabat, Baptiste Dazas, Alfred Delville, Eric Ferrage, Fabien Hubert, Mónica Jiménez-Ruiz, Laurent J. Michot, Sébastien Savoye, Emmanuel Tertre
      First page: 34
      Abstract: This review details a large panel of experimental studies (Inelastic Neutron Scattering, Quasi-Elastic Neutron Scattering, Nuclear Magnetic Resonance relaxometry, Pulsed-Gradient Spin-Echo attenuation, Nuclear Magnetic Resonance Imaging, macroscopic diffusion experiments) used recently to probe, over a large distribution of characteristic times (from pico-second up to days), the dynamical properties of water molecules and neutralizing cations diffusing within clay/water interfacial media. The purpose of this review is not to describe these various experimental methods in detail but, rather, to investigate the specific dynamical information obtained by each of them concerning these clay/water interfacial media. In addition, this review also illustrates the various numerical methods (quantum Density Functional Theory, classical Molecular Dynamics, Brownian Dynamics, macroscopic differential equations) used to interpret these various experimental data by analyzing the corresponding multi-scale dynamical processes. The purpose of this multi-scale study is to perform a bottom-up analysis of the dynamical properties of confined ions and water molecules, by using complementary experimental and numerical studies covering a broad range of diffusion times (between pico-seconds up to days) and corresponding diffusion lengths (between Angstroms and centimeters). In the context of such a bottom-up approach, the numerical modeling of the dynamical properties of the diffusing probes is based on experimental or numerical investigations performed on a smaller scale, thus avoiding the use of empirical or fitted parameters.
      Citation: Colloids and Interfaces
      PubDate: 2021-06-15
      DOI: 10.3390/colloids5020034
      Issue No: Vol. 5, No. 2 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 2: Improved As-Synthesized Oleic
           Amido Propyl Betaine Surfactant Mixture for Stable Ultra-Low Interfacial
           Tension: Effect of Mixed Co-Solvents

    • Authors: Norhidayah Ahmad Wazir, Wasan Saphanuchart, Anita Ramli, Nurida Yusof
      First page: 2
      Abstract: As-synthesized oleic amido propyl betaine surfactant mixture, that was produced through a “direct formulation through synthesis” process, exhibited ultra-low oil/water interfacial tension (IFT) values as low as 3.5 × 10−4 mN/m when dissolved in seawater at a reservoir temperature of 96 °C. The as-synthesized surfactant, which was left untreated, had a slightly cloudy appearance when mixed with seawater. Polar solvents were introduced to this surfactant to improve its aqueous solubility by changing its overall hydrophilicity, particularly on the oil/water interface. In this study, two types of glycol ether co-solvent, i.e., ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, were used at different concentrations in a single application and as a mixture of co-solvents at a certain ratio. The behavior of the as-synthesized surfactant with the presence of these co-solvents was investigated. As a result, it showed that the co-solvent helps in solubility improvement and alters the interfacial tension behavior of the surfactant. Ethylene glycol monobutyl ether was found to be efficient in maintaining an ultra-low IFT value of the surfactant. However, the aqueous solubility of the surfactant was not significantly improved. In contrast, the addition of diethylene glycol monobutyl ether showed improvement of the aqueous solubility of the surfactant, but it tends to increase the IFT above ultra-low value. Based on this understanding, a set of co-solvent mixing ratios were tested, and the results showed further improvement in both the oil/water interfacial tension behavior and surfactant aqueous solubility. The most stable oil/water IFT of 3.36 × 10−3 mN/m and clearer surfactant solutions were obtained for ratio C at 35 wt.% presence of co-solvent.
      Citation: Colloids and Interfaces
      PubDate: 2021-01-06
      DOI: 10.3390/colloids5010002
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 3: Adsorption Properties of Soft
           Hydrophobically Functionalized PSS/MA Polyelectrolytes

    • Authors: Ewelina Jarek, Zofia Krasińska-Krawet, Tomasz Kruk, Łukasz Lamch, Sylwia Ronka, Kazimiera A. Wilk, Piotr Warszyński
      First page: 3
      Abstract: We investigated the adsorption properties of the newly synthesized, hydrophobically functionalized polyelectrolyte (HF-PE), poly(4-styrenesulfonic-co-maleic acid) copolymer (PSS/MA). The hydrophobic alkyl side chains (C12 or C16) were incorporated into the polyelectrolyte backbone via the labile amid linker to obtain the soft HF-PE product with the assumed amount of 15% and 40% degree of grafting for every length of the alkyl chain, i.e., PSS/MA-g-C12NH2 (15% or 40%) as well as PSS/MA-g-C16NH2 (15% or 40%). In the present contribution, we determined both the effect of grafting density and the length of alkyl chain on adsorption at water/air and water/decane interfaces, as well as on top of the polyelectrolyte multilayer (PEM) deposited on a solid surface. The dependence of the interfacial tension on copolymer concentration was investigated by the pendant drop method, while the adsorption at solid surface coated by poly(diallyldimethylammonium chloride)/poly(styrene sulphonate) PEM by the quartz crystal microbalance with dissipation (QCM-D), attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and contact angle analysis. We found that surface activity of the hydrophobized copolymer was practically independent of the grafting ratio for C16 side chains, whereas, for C12, the copolymer with a lower grafting ratio seemed to be more surface active. The results of QCM-D and FTIR-ATR experiments confirmed the adsorption of hydrophobized copolymer at PEM along with the modification of water structure at the interface. Finally, it can be concluded that the hydrophobically modified PSS/MA can be successfully applied either as the efficacious emulsifier for the formation of (nano)emulsions for further active substances encapsulation using the sequential adsorption method or as one of the convenient building blocks for the surface modification materials.
      Citation: Colloids and Interfaces
      PubDate: 2021-01-14
      DOI: 10.3390/colloids5010003
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 4: What Can You Learn about
           Apparent Surface Free Energy from the Hysteresis Approach'

    • Authors: Konrad Terpiłowski, Lucyna Hołysz, Michał Chodkowski, David Clemente Guinarte
      First page: 4
      Abstract: The apparent surface free energy is one of the most important quantities in determining the surface properties of solids. So far, no method of measuring this energy has been found. The essence of contact angle measurements is problematic. Contact angles should be measured as proposed by Young, i.e., in equilibrium with the liquid vapors. This type of measurement is not possible because within a short time, the droplet in the closed chamber reaches equilibrium not only with vapors but also with the liquid film adsorbed on the tested surface. In this study, the surface free energy was determined for the plasma-activated polyoxymethylene (POM) polymer. Activation of the polymer with plasma leads to an increase in the value of the total apparent surface free energy. When using the energy calculations from the hysteresis based approach (CAH), it should be noted that the energy changes significantly when it is calculated from the contact angles of a polar liquid, whereas being calculated from the angles of a non-polar liquid, the surface activation with plasma changes its value slightly.
      Citation: Colloids and Interfaces
      PubDate: 2021-01-14
      DOI: 10.3390/colloids5010004
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 5: Acknowledgment to Reviewers of
           Colloids and Interfaces in 2020

    • Authors: Colloids; Interfaces Editorial Office
      First page: 5
      Abstract: Peer review is the driving force of journal development, and reviewers are gatekeepers who ensure that Colloids and Interfaces maintains its standards for the high quality of its published papers [...]
      Citation: Colloids and Interfaces
      PubDate: 2021-01-18
      DOI: 10.3390/colloids5010005
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 6: Experimental Data Contributing
           to the Elusive Surface Charge of Inert Materials in Contact with Aqueous
           Media

    • Authors: Antun Barišić, Johannes Lützenkirchen, Nikol Bebić, Qinzhi Li, Khalil Hanna, Andrey Shchukarev, Tajana Begović
      First page: 6
      Abstract: We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these surfaces acquired less charge from proton-related reactions than oxide minerals. The data from batch-type titrations for PTFE powder did not show an effect of ionic strength, which was also in contrast with results for classical colloids. In agreement with classical colloids, the electrokinetic results for inert surfaces showed the typical salt level dependence. In some cases, the point of zero net proton charge as determined from mass and tentatively from acid–base titration differed from isoelectric points, which has also been previously observed, for example by Chibowski and co-workers for ice electrolyte interfaces. Finally, we found no evidence for surface contaminations of our PTFE particles before and after immersion in aqueous solutions. Only in the presence of NaCl-containing solutions did cryo-XPS detect oxygen from water. We believe that our low isoelectric points for PTFE were not due to impurities. Moreover, the measured buffering at pH 3 could not be explained by sub-micromolar concentrations of contaminants. The most comprehensive explanation for the various sets of data is that hydroxide ion accumulation occurred at the interfaces between inert surfaces and aqueous solutions.
      Citation: Colloids and Interfaces
      PubDate: 2021-01-23
      DOI: 10.3390/colloids5010006
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 7: Surface Activity of Natural
           Surfactants Extracted from Sapindus mukorossi and Sapindus trifoliatus
           Soapnuts

    • Authors: Patrycja Wojtoń, Magdalena Szaniawska, Lucyna Hołysz, Reinhard Miller, Aleksandra Szcześ
      First page: 7
      Abstract: Surfactants derived from renewable sources such as plants are an ecological alternative to synthetic surfactants. Aqueous solutions of natural surfactants extracted from soapnuts obtained from two plants, Sapindus mukorossi and Sapindus trifoliatus, were studied. Their properties in terms of surface tension reduction and wettability were examinated. The natural surfactants show the ability to reduce the surface tension and increase the wettability of the hydrophobic polytetrafluoroethylene surface. These nuts can be used repeatedly for washing also in hard water. Crude extracts from Sp. trifoliatus exhibit better surface properties than those from Sp. mukorossi. This makes these soapnuts a good potential source of biosurfactants for household use.
      Citation: Colloids and Interfaces
      PubDate: 2021-01-31
      DOI: 10.3390/colloids5010007
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 8: Dependency of Contact Angles on
           Three-Phase Contact Line: A Review

    • Authors: H. Yildirim Erbil
      First page: 8
      Abstract: The wetted area of a sessile droplet on a practical substrate is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, contact angles of droplets have been studied for more than two hundred years, there are still some unanswered questions. In the last two decades, it was experimentally proven that the advancing and receding contact angles, and the contact angle hysteresis of rough and chemically heterogeneous surfaces, are determined by interactions of the liquid and the solid at the three-phase contact line alone, and the interfacial area within the contact perimeter is irrelevant. However, confusion and misunderstanding still exist in this field regarding the relationship between contact angle and surface roughness and chemical heterogeneity. An extensive review was published on the debate for the dependence of apparent contact angles on drop contact area or the three-phase contact line in 2014. Following this old review, several new articles were published on the same subject. This article presents a review of the novel articles (mostly published after 2014 to present) on the dependency of contact angles on the three-phase contact line, after a short summary is given for this long-lasting debate. Recently, some improvements have been made; for example, a relationship of the apparent contact angle with the properties of the three-phase line was obtained by replacing the solid–vapor interfacial tension term, γSV, with a string tension term containing the edge energy, γSLV, and curvature of the triple contact line, km, terms. In addition, a novel Gibbsian thermodynamics composite system was developed for a liquid drop resting on a heterogeneous multiphase and also on a homogeneous rough solid substrate at equilibrium conditions, and this approach led to the same conclusions given above. Moreover, some publications on the line energy concept along the three-phase contact line, and on the “modified” Cassie equations were also examined in this review.
      Citation: Colloids and Interfaces
      PubDate: 2021-02-01
      DOI: 10.3390/colloids5010008
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 9: Interfacial Tension Sensor for
           Low Dosage Surfactant Detection

    • Authors: Piotr Pawliszak, Bronwyn H. Bradshaw-Hajek, Christopher Greet, William Skinner, David A. Beattie, Marta Krasowska
      First page: 9
      Abstract: Currently there are no available methods for in-line measurement of gas-liquid interfacial tension during the flotation process. Microfluidic devices have the potential to be deployed in such settings to allow for a rapid in-line determination of the interfacial tension, and hence provide information on frother concentration. This paper presents the development of a simple method for interfacial tension determination based on a microfluidic device with a flow-focusing geometry. The bubble generation frequency in such a microfluidic device is correlated with the concentration of two flotation frothers (characterized by very different adsorption kinetic behavior). The results are compared with the equilibrium interfacial tension values determined using classical profile analysis tensiometry.
      Citation: Colloids and Interfaces
      PubDate: 2021-02-03
      DOI: 10.3390/colloids5010009
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 10: Foam Quality of Foams Formed on
           Capillaries and Porous Media Systems

    • Authors: Victor Starov, Anna Trybala, Phillip Johnson, Mauro Vaccaro
      First page: 10
      Abstract: Foams are of great importance as a result of their expansive presence in everyday life—they are used in the food, cosmetic, and process industries, and in detergency, oil recovery, and firefighting. There is a little understanding of foam formation using soft porous media in terms of the quality of foam and foam formation. Interaction of foams with porous media has recently been investigated in a study by Arjmandi-Tash et al., where three different regimes of foam drainage in contact with porous media were observed. In this study, the amount of foam generated using porous media with surfactant solutions is investigated. The aim is to understand the quality of foam produced using porous media. The effect of capillary sizes and arrangement of porous in porous media has on the quality of foam is investigated. This is then followed by the use of soft porous media for foam formation to understand how the foam is generated on the surface of the porous media and the effect that different conditions (such as concentration) have on the quality of the foam. The quality of foam is a blanket term for bubble size, liquid volume fraction, and stability of the foam. The liquid volume fraction is calculated using a homemade dynamic foam analyser, which is used to obtain the distribution of liquid volume fraction along with the foam height. Soft porous media does not influence substantially the rate of decay of foam produced, however, it decreases the average diameter of the bubbles, whilst increasing the range of bubble sizes due to the wide range of pore sizes present in the soft porous media. The foam analyser showed the expected behaviour that, as the foam decays and becomes drier, the liquid volume fraction of the foam falls, and therefore the conductivity of foam also decreases, indicating the usefulness of the home-made device for future investigations.
      Citation: Colloids and Interfaces
      PubDate: 2021-02-08
      DOI: 10.3390/colloids5010010
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 11: Hydrodynamic Boundary Layers at
           Solid Wall—A Tool for Separation of Fine Solids

    • Authors: Ljubomir Nikolov
      First page: 11
      Abstract: A theoretical study is performed about the hydrodynamic interaction of fine species entrapped in the boundary layer (BL) at solid wall (plate). The key starting point is the analysis of the disturbance introduced by solid spheres in the background fluid flow. For a neutrally buoyant entity, the type of interaction is determined by the size of the spheres as compared to the thickness of the BL region. The result is granulometric separation of the solids inside the BL domain at the wall. The most important result in view of potential applications concerns the so-called small particles Rp < L/ReL5/4 (ReL is the Reynolds number of the background flow and Rp is the radius of the entrapped sphere). In the case of non-neutrally buoyant particles, gravity interferes with the separation effect. Important factor in this case is the relative density of the solid species as compared to this of the fluid. In view of further practical uses, particles within the range of Δρ/ρ < Fr2/ReL1/2 (Fr is Froude number and Δρ/ρ is the relative density of the entrapped solids) are systematically studied. The trajectories inside the BL region of the captured species are calculated. The obtained data show that there are preferred regions along the wall where the fine solids are detained. The results are important for the assessment of the general efficiency of entrapment and segregation of fine species in the vicinity of solid walls and have high potential for further design of industrial separation processes.
      Citation: Colloids and Interfaces
      PubDate: 2021-02-11
      DOI: 10.3390/colloids5010011
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 12: Evaporation of Sessile Droplets
           of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

    • Authors: Andrew Akanno, Lionel Perrin, Eduardo Guzmán, Sara Llamas, Victor M. Starov, Francisco Ortega, Ramón G. Rubio, Manuel G. Velarde
      First page: 12
      Abstract: The wetting and evaporation behavior of droplets of aqueous solutions of mixtures of poly(diallyldimethylammonium chloride) solution, PDADMAC, with two different anionic surfactants, sodium laureth sulfate, SLES, and sodium N-lauroyl N-methyl taurate, SLMT, were studied in terms of the changes of the contact angle θ and contact length L of sessile droplets of the mixtures on silicon wafers at a temperature of 25 °C and different relative humidities in the range of 30–90%. The advancing contact angle θa was found to depend on the surfactant concentration, independent of the relative humidity, with the mixtures containing SLES presenting improved wetting behaviors. Furthermore, a constant droplet contact angle was not observed during evaporation due to pinning of the droplet at the coffee-ring that was formed. The kinetics for the first evaporation stage of the mixture were independent of the relative humidity, with the evaporation behavior being well described in terms of the universal law for evaporation.
      Citation: Colloids and Interfaces
      PubDate: 2021-02-16
      DOI: 10.3390/colloids5010012
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 13: Synthesis of Monoclinic
           Vanadium Dioxide via One-Pot Hydrothermal Route

    • Authors: Guowei Liu, Zengyan Du, Ming Li, Yi Long
      First page: 13
      Abstract: Pure monoclinic vanadium dioxide nanoparticles (VO2 NPs) with a controlled uniform size are considered essential for the preparation of thermochromic smart window coatings on desired substrates. Herein, we report a facile one-step hydrothermal synthesis of VO2(M) NPs without post-treatment of annealing, which may induce unwanted aggregation of NPs. In contrast with the annealed sample, the one-step processed VO2(M) NPs exhibit superior thermochromic performance with the solar modulation efficiency of 11.8% and luminous transmittance of 37.3%.
      Citation: Colloids and Interfaces
      PubDate: 2021-02-16
      DOI: 10.3390/colloids5010013
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 14: β-Lactoglobulin Adsorption
           Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of
           State Revisited, Impact of pH

    • Authors: Georgi G. Gochev, Volodymyr I. Kovalchuk, Eugene V. Aksenenko, Valentin B. Fainerman, Reinhard Miller
      First page: 14
      Abstract: The theoretical description of the adsorption of proteins at liquid/fluid interfaces suffers from the inapplicability of classical formalisms, which soundly calls for the development of more complicated adsorption models. A Frumkin-type thermodynamic 2-d solution model that accounts for nonidealities of interface enthalpy and entropy was proposed about two decades ago and has been continuously developed in the course of comparisons with experimental data. In a previous paper we investigated the adsorption of the globular protein β-lactoglobulin at the water/air interface and used such a model to analyze the experimental isotherms of the surface pressure, Π(c), and the frequency-, f-, dependent surface dilational viscoelasticity modulus, E(c)f, in a wide range of protein concentrations, c, and at pH 7. However, the best fit between theory and experiment proposed in that paper appeared incompatible with new data on the surface excess, Γ, obtained from direct measurements with neutron reflectometry. Therefore, in this work, the same model is simultaneously applied to a larger set of experimental dependences, e.g., Π(c), Γ(c), E(Π)f, etc., with E-values measured strictly in the linear viscoelasticity regime. Despite this ambitious complication, a best global fit was elaborated using a single set of parameter values, which well describes all experimental dependencies, thus corroborating the validity of the chosen thermodynamic model. Furthermore, we applied the model in the same manner to experimental results obtained at pH 3 and pH 5 in order to explain the well-pronounced effect of pH on the interfacial behavior of β-lactoglobulin. The results revealed that the propensity of β-lactoglobulin globules to unfold upon adsorption and stretch at the interface decreases in the order pH 3 > pH 7 > pH 5, i.e., with decreasing protein net charge. Finally, we discuss advantages and limitations in the current state of the model.
      Citation: Colloids and Interfaces
      PubDate: 2021-03-05
      DOI: 10.3390/colloids5010014
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 15: Nanocomposite Inks Based on
           Nickel–Silver Core–Shell and Silver Nanoparticles for Fabrication
           Conductive Coatings at Low-Temperature Sintering

    • Authors: Anna Pajor-Świerzy, Franciszek Szendera, Radosław Pawłowski, Krzysztof Szczepanowicz
      First page: 15
      Abstract: Nanocomposite inks composed of nickel–silver core–shell and silver nanoparticles (NPs) can combine the advantages of lower cost, high conductivity, and low-temperature sintering processes, which have attracted much attention in the development of materials for printed flexible electronics. In this context, in the present paper, we report the process of preparation of nanocomposite ink containing nickel–silver core–shell nanoparticles, as the main filler, and silver nanoparticles, as doping material, and their application for the fabrication of conductive coatings. It was found that the addition of a low concentration of Ag NPs to ink formulation based mainly on low-cost Ni-Ag NPs improves the conductive properties of coatings fabricated by ink deposition on a glass substrate. Two types of prepared nanocomposite ink coatings showed promising properties for future application: (1) doped with 0.5% of Ag NPs sintered at 200 °C as low cost for larger industrial application and, (2) containing 1% of Ag NPs sintered at 150 °C for the fabrication of conductive printed patterns on flexible substrates. The conductivity of such nanocomposite films was similar, about of 6 × 106 S/m, which corresponds to 35% of that for a bulk nickel.
      Citation: Colloids and Interfaces
      PubDate: 2021-03-08
      DOI: 10.3390/colloids5010015
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 16: Thermodynamics, Kinetics and
           Dilational Visco-Elasticity of Adsorbed CnEOm Layers at the Aqueous
           Solution/Air Interface

    • Authors: Valentin B. Fainerman, Volodymyr I. Kovalchuk, Eugene V. Aksenenko, Francesca Ravera, Libero Liggieri, Giuseppe Loglio, Alexander V. Makievski, Emanuel Schneck, Reinhard Miller
      First page: 16
      Abstract: The adsorption behaviour of linear poly(oxyethylene) alkyl ether (CnEOm) is best described by a reorientation model. Based on a complete set of experimental data, including the adsorption kinetics, the equilibrium surface tension isotherm and the surface dilational visco-elasticity, the thermodynamic and kinetic adsorption parameters for some CnEOm at the water/air interface were determined. For the study, six CnEOm surfactants were selected (n = 10, 12 and 14 and m = 4, 5 and 8) and were studied by bubble profile analysis and maximum bubble pressure tensiometry. A refined theoretical model based on a reorientation-adsorption model combined with a diffusion-controlled adsorption kinetics and exchange of matter allowed us to calculate the surface layer composition by adsorbing molecules in different orientations. It turns out that at larger surface coverage, the adsorption rate decreases, i.e., the apparent diffusion coefficients are smaller. This deceleration can be explained by the transition of molecules adsorbed in a state of larger molar surface area into a state with smaller molar surface area.
      Citation: Colloids and Interfaces
      PubDate: 2021-03-16
      DOI: 10.3390/colloids5010016
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 17: Dynamic Measurements with the
           Bicone Interfacial Shear Rheometer: The Effects of the Numerical
           Implementation of the Interfacial Boundary Condition

    • Authors: Pablo Sánchez-Puga, Javier Tajuelo, Juan Manuel Pastor, Miguel A. Rubio
      First page: 17
      Abstract: The increasing popularity of flow field-based data analysis (FFBDA) techniques has a paradigmatic example in the routines already developed for the rotational oscillating bicone bob interfacial shear rheometer. Such routines use a second order centered finite difference (SOCFD) discretization scheme, in both the vertical and radial coordinates, for the velocity field in the bulk fluid subphase and a first order forward finite difference (FOFFD) scheme in the vertical coordinate for the velocity field at the air/water interface. Such a mixture of schemes causes non-smooth flow fields at the interface that can be tackled by appropriately devising a SOCFD scheme for the vertical coordinate at the interface using a line of “phantom” nodes that merely serve to adequately merge the Navier–Stokes equations and the Boussinesq–Scriven boundary condition at the interface. Here we report on a detailed analysis of the quantitative improvements of such a scheme over the previous one by comparing the structure of the flow fields at and close to the interface, the differences in the interfacial and bulk drag torques on the bicone bob, and the differences in the torque/displacement complex amplitude ratio.
      Citation: Colloids and Interfaces
      PubDate: 2021-03-17
      DOI: 10.3390/colloids5010017
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 18: Recent Advances in
           Nanomaterials for Dermal and Transdermal Applications

    • Authors: Amani Zoabi, Elka Touitou, Katherine Margulis
      First page: 18
      Abstract: The stratum corneum, the most superficial layer of the skin, protects the body against environmental hazards and presents a highly selective barrier for the passage of drugs and cosmetic products deeper into the skin and across the skin. Nanomaterials can effectively increase the permeation of active molecules across the stratum corneum and enable their penetration into deeper skin layers, often by interacting with the skin and creating the distinct sites with elevated local concentration, acting as reservoirs. The flux of the molecules from these reservoirs can be either limited to the underlying skin layers (for topical drug and cosmeceutical delivery) or extended across all the sublayers of the epidermis to the blood vessels of the dermis (for transdermal delivery). The type of the nanocarrier and the physicochemical nature of the active substance are among the factors that determine the final skin permeation pattern and the stability of the penetrant in the cutaneous environment. The most widely employed types of nanomaterials for dermal and transdermal applications include solid lipid nanoparticles, nanovesicular carriers, microemulsions, nanoemulsions, and polymeric nanoparticles. The recent advances in the area of nanomaterial-assisted dermal and transdermal delivery are highlighted in this review.
      Citation: Colloids and Interfaces
      PubDate: 2021-03-18
      DOI: 10.3390/colloids5010018
      Issue No: Vol. 5, No. 1 (2021)
       
  • Colloids and Interfaces, Vol. 5, Pages 19: Electroosmosis and Electric
           Conduction of Electrolyte Solutions in Charge-Regulating Fibrous Media

    • Authors: Wei L. Chen, Huan J. Keh
      First page: 19
      Abstract: An analytical study of the electroosmosis and electric conduction of electrolyte solutions in a fibrous medium composed of parallel charge-regulating cylinders with arbitrary electric double layer thickness is presented. A linearized charge regulation model was adopted for the association and dissociation reactions occurring at the amphoteric functional groups over the surfaces of the cylinders, and a unit cell model was employed to accommodate interactions among the cylinders. The electrokinetic equations governing the ionic concentration, electric potential, and liquid flow fields were solved at low zeta potential for the cylinders. Explicit formulas for the electroosmotic mobility and effective electric conductivity in the fiber matrix were obtained. The results indicate that the charge regulation characteristics, such as the equilibrium constants of the reactions occurring at the cylinders’ surfaces and the bulk concentration of the charge-determining ions, influence the surface charge density and potential, electroosmotic mobility, and effective electric conductivity substantially.
      Citation: Colloids and Interfaces
      PubDate: 2021-03-19
      DOI: 10.3390/colloids5010019
      Issue No: Vol. 5, No. 1 (2021)
       
 
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