Abstract: Abstract
Literature data on molecular mobility in glassy polymers have been analyzed. It has been shown that, in the temperature range corresponding to the glassy state of a polymer, a largescale (segmental) molecular motion is possible, with this motion being responsible for the physical (thermal) aging of the polymer. Heating of an aged polymer restores its initial state, and the aging process begins again (effect of “rejuvenation”). At the same time, aging processes may be initiated by a mechanical action on a glassy polymer. It is sufficient to subject an aged polymer to a mechanical action to transfer it to a state characteristic of a polymer heated above the glasstransition temperature. It should be noted that deformation of a glassy polymer is nonuniform over its volume and occurs in local zones (shear bands and/or crazes). It is of importance that these zones contain an oriented fibrillized polymer with fibril diameters of a few to tens of nanometers, thereby giving rise to the formation of a developed interfacial surface in the polymer. The analysis of the published data leads to a conclusion that the aging of a mechanically “rejuvenated” polymer is, as a matter of fact, the coalescence of nanosized structural elements (fibrils), which fill the shear bands and/or crazes and have a glasstransition temperature decreased by tens of degrees. PubDate: 20160501
Abstract: Abstract
A set of equations has been derived for the nonstationary composition, size, and temperature of a growing or evaporating multicomponent microdroplet of a nonideal solution under arbitrary initial conditions. Equations for local nonstationary diffusion molecular and heat fluxes in a mixture of a multicomponent vapor with a noncondensable carrier gas have been obtained within the framework of nonequilibrium thermodynamics with allowance for hydrodynamic flow of the medium. The derived closed set of equations takes into account the nonstationarity of the diffusion and heat transfer, effect of thermodiffusion and other cross effects in the multicomponent vapor–gas medium, the Stefan flow, and droplet boundary motion, as well as the nonideality of the solution in the droplet. The general approach has been illustrated by the consideration of the multicomponent medium at low concentrations of vapors taking into account its thermal expansion due to the Stefan flow in the case of a nonstationary diffusion regime of the nonisothermal condensation growth of a onecomponent droplet. PubDate: 20160501
Abstract: Abstract
The formation processes, structure, geometric parameters, and conductivity are studied for thin composite films prepared from nanodispersions of silver particles with diameters smaller than 10 nm by the moving meniscus method. The thickness and conductivity of the films are determined as functions of the mass concentration of a precursor (AgNO3) and the concentration (size) of silver nanoparticles. Some of these functions are nonmonotonic. The dependences of the conductivity on these parameters are found to have the character of a percolation transition. Heterogeneous crystallization of soluble components of the colloidal solutions on silver nanoparticles plays an essential role in the formation of the films. PubDate: 20160501
Abstract: Abstract
The manyparticle tightbinding potential has been employed to calculate the specific surface energy of icosahedral nanoclusters of transition metals. The equimolecular surface has been considered as the dividing surface. The surface energy has been shown to linearly increase with particle size at nanocluster radii smaller than five radii of the first coordination sphere. As the nanocluster radius is further enlarged, the surface energy passes through a maximum and approaches an asymptotic macroscopic value. The coefficients of proportionality between the specific surface energy and nanocluster radius have been found and compared with the data available from the literature. PubDate: 20160501
Abstract: Abstract
Results of numerical solution have been presented for a set of equations describing the nonstationary and nonisothermal growth or evaporation of microdroplets consisting of ethanol and water, sulfuric acid and water, and sulfuric and nitric acids and water. Time dependences of droplet size, temperature, and composition have been determined at low concentrations of a condensable vapor, as compared with the concentration of a carrier gas in an ambient vapor–gas mixture. The calculations have been performed using different initial conditions and approximations for the dependences of saturation vapor pressures, activity coefficients, and partial heats of condensation of the components, as well as average volumes per molecule on droplet composition and temperature. By the examples of ethanol–water and sulfuric acid–water droplets, it has been shown that nonmonotonic variations in the droplet radius are possible. Regimes of nonmonotonic variations in the temperature of a droplet that precede the onset of its stationary growth or evaporation have been revealed for all systems under consideration. PubDate: 20160501
Abstract: Abstract
Kinetic regularities of flocculation of model kaolin suspensions by highly substituted cationic flocculants synthesized from different starches (corn, waxy corn, potato, and tapioca starches) have been studied as depending on the doses and vegetable origins of the flocculants. The rate of kaolin suspension flocculation has been found to increase with the dose of the cationic starches of all types. It has been shown that, irrespective of the dose, the highest rate of kaolin sedimentation in the model systems is observed in the presence of cationic potato starch. It has been demonstrated that cationic potato starch flocculates kaolin suspensions with concentrations of 0.1, 0.5, and 1.0% with the same efficiency. In this case, the suspensions are almost completely clarified within 2–5 min. Moreover, the dependence of the flocculating efficiency for a 0.1% model suspension on the dose of cationic starch has been found to pass through a maximum at a starch content of 1.0–5.0 mg/g of kaolin depending on the type of starch. PubDate: 20160501
Abstract: Abstract
Distilled water droplet evaporation has been studied on copper substrate surfaces with different degrees of roughness. Data on variations in the contact diameter have been employed to distinguish between the regimes of distilled water droplet spreading over the copper surfaces that proceed after the viscous regime. For each isolated regime, the duration has been determined as a fraction of the total evaporation time and the main physical processes have been described. Variations in contact angles have been analyzed as depending on copper surface temperature. It has been established that, as the substrate temperature is elevated, wetting becomes better, while the adhesion work remains almost unchanged, thereby indicating the absence of chemical and structural transformations at the liquid–substrate interface. PubDate: 20160501
Abstract: Abstract
Two approaches to determining critical micelle concentration (CMC) are assessed, i.e., from the inflection point in the curve for the concentration dependence of the degree of micellization and as K
1/(1–n), where K is the constant of the law of mass action and n is the aggregation number. The latter approach makes the theory simpler, while the former explicitly expresses the critical degree of micellization via the aggregation number. The concentrations of monomers and micelles are analyzed as functions of the overall concentration of a surfactant in a micellar solution. These functions look much simpler in the graphical form as compared with their complex exact analytical representation. This has resulted in derivation of simple analytical approximations for these functions, with these approximations being useful for calculations. The concentration dependence of the surfactant diffusion coefficient has been considered based on these approximations. It turned out that this dependence not only provides the known method for determining the diffusion coefficient of micelles, but also gives the possibility in principle to determine the aggregation number from the slope of the dependence of the diffusion coefficient on the inverse concentration (counted from the CMC in the CMC units). This new method for determining the aggregation number has been tested using the literature data on the diffusion coefficient of penta(ethylene glycol)1hexyl ether in an aqueous solution. PubDate: 20160501
Abstract: Abstract
Smectites are widely used minerals whose structure and properties can be modified and controlled. The aim of this study was to improve the sorption capacity and accessibility of interlayer (interpacket) spaces by reducing the pillar density in Chmielnik smectite. The micropore volume increases by increasing one of their dimensions, which is determined as the distance between pillars. This aim was achieved by lowering the resultant packet charge. Changes in intercalate structure and microporosity were studied using Xray diffractometry and Ar sorption at–196°C. The Li/Na smectite ratio is crucial for modifying the smectite properties, particularly those associated with mineral microporosity. The behavior of the samples with the same interlayer cation composition exhibited two distinct trends. The first one is a decrease in the specific surface value (volume of micropores) accompanied by an increase in the amount of Li in the ion interlayer composition. The second one is a decline in the specific surface (volume of micropores) when the calcination temperature rises. PubDate: 20160501
Abstract: Abstract
A threelayer model of an electrical double layer at magnetite/aqueous 0.001–1 mol/L KCl solution interfaces has been considered in a pH range of 3.5–9.5. A procedure has been proposed for determining the constants of equilibrium reactions and the parameters of electrical double layers from the acid–base potentiometric titration data of magnetite suspensions in the solutions taking into account the generation of a surface charge. The determination of these constants and the parameters of the electrical double layer is based on the use of the point of zero charge. Software has been developed and used for calculating the main parameters of the electrical double layer within the framework of the threelayer model and the Graham–Parsons concepts. PubDate: 20160501
Abstract: Abstract
A simple and easy method based on differential drying of samples at different temperatures has been proposed for quantitative determination of the specific surface areas of colloidal disperse systems. The following fundamental dependence of moisture thermodynamic potential [ψ] on absolute drying temperature T is used in the method: ψ = Q–aT, where Q is the specific heat of evaporation and a is a parameter related to the initial temperature and relative air humidity in an external thermodynamic reservoir (laboratory apartment). Gravimetric data on moisture mass fraction W and the value of ψ have been used to plot Polanyi potential curves W(ψ) for the studied samples. The curves have been employed to calculate the isotherms of moisture sorption. The capacity of a monolayer and the effective specific surface area have been determined from these isotherms in terms of the BET theory. The surface area estimated from the published results of classical experiments is about 1000 m2/g. The problem of the “absolute zero of humidity,” which is of great importance for determining the properties of colloidal disperse bodies normalized with respect to the solid phase mass, has been discussed. PubDate: 20160501
Abstract: Abstract
Methane elution from helium flowing through a sample of Cu3(BTC)2 metalorganic framework material has been studied by gas chromatography. The efficiency of a short adsorbent layer has been calculated in terms of a version of the moments method assuming that there are additive contributions to the variance and retention from both the input pulse (or the extracolumn effects) and the processes of substance movement in the flow of the mobile phase through the permeable porous adsorbent. It has been found that the efficiency or the relative length of the layer of the studied metalorganic material sample, as calculated by the moments method, is considerably lower than the values observed for microporous activated carbon. PubDate: 20160501
Abstract: Abstract
The asymmetry of the current–voltage characteristics of ionexchange membranes is explained in terms of the model of a bilayer fine porous membrane with constant charge distributions over the thickness of layers. This model has previously been proposed for determining diffusion permeability of membranes. In the case of one uncharged (neutral) layer, a set of two implicit algebraic equations is derived for determining the total current–voltage characteristics (CVC) of a membrane. For the first time, implicit algebraic equations are obtained for calculating the limiting currents at different orientations of an anisotropic membrane in an electrodialysis cell and explicit expressions are derived for determining specific conductivity of the membrane from the slope of the ohmic region of a CVC under the approximation of “excluded coions.” The model may be successfully used for describing the CVCs of perfluorinated MF4SC sulfonic cationexchange membranes, the surface layers of which are modified with polyaniline or halloysite. PubDate: 20160501
Abstract: Abstract
The dustygas model has been extended to the case of nanoporous media, in which the action of surface forces must be taken into account. A basic set of transport equations underlying the model has been derived proceeding from a set of kinetic equations for an ordinary gas and dust particles. In the kinetic equations, the interaction between the gas and dust particles is represented as a sum of a longrange (analog of surface forces) and shortrange components. The contribution of the longrange component has been taken into account in the selfconsistent approximation, while the shortrange component has been considered in the standard manner. Allowance for the surface forces has been shown to result in a substantial modification of the equation for gas transport through porous bodies, with this modification being most pronounced at nonuniform temperatures. PubDate: 20160501
Abstract: Abstract
The onestage unseeded method of the synthesis of gold nanorods has been employed to systematically study the influence of process temperature on nanorods sizes and plasmon resonance properties. It has been shown for the first time that even slight variations in the temperature have a very strong effect on these characteristics. Analysis of the obtained results has indicated that the observed effect is caused by the influence of temperature on the nucleation rate of the nanoparticles. PubDate: 20160501
Abstract: Abstract
Dissociation constants of DLalanylDLmethionine have been determined in water and micellar solutions of surfactants (anionic sodium ndodecyl sulfate, cationic cetylpyridinium chloride, and nonionic Brij 35). It has been established that CuA+ and CuH–1A complexes are formed in water and micellar solutions of sodium ndodecyl sulfate, while CuA+, CuH–1A, and Cu–2A– complexes are formed in micellar solutions of cetylpyridinium chloride and Brij 35. Stability of the complexes depends on micelle surface charge and degrees of binding of individual chemical forms by a micellar pseudophase. PubDate: 20160501
Abstract: Abstract
Dualseeded dispersion polymerization (DSDP) of 2ethylhexyl methacrylate with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed beads in the presence of saturated hydrocarbon droplets followed by evaporation of the hydrocarbon was studied. The effect of various polymerization conditions including initiator type and content, stabilizer type and concentration, and different hydrocarbon’s content on the shape of the obtained particles was investigated. The increase of concentration of 2,2'azobis(isobutyronitrile) (AIBN) had no effect on the shape of the produced almondshelllike PS particles, although it contributes in the formation of associated composite particles along with larger poly(2ethylhexyl methacrylate) (PEHMA) beads produced by secondary nucleation. The experimental results showed that other initiators led to the formation of stable golfballlike PMMA particles as well as PS ones with symmetric shape. The type of stabilizer did not affect the shape of the particles. This observation suggests that unique almondshelllike PS particles can be produced through a stabilizerfree DSDP process. The lowering of the concentration of hydrocarbons with long alkyl chains yielded stable disclike PMMA particles. The formation of functional almondshelllike particles by using light hydrocarbons was another interesting finding of this research. PubDate: 20160501
Abstract: Abstract
The possibility of development of electrical percolation upon variations in the contents of components in a disperse system has been studied in terms of Bruggeman’s ideas of an effective medium and the continual model of the electrical conductivity of composite materials. The case of a small difference between the specific conductivities of a dispersed phase K
m and a dispersion medium K
d has been considered. It has been shown that the dependence of electrical conductivity K of a disperse system on volume fraction p of a wellconducting component may exhibit an inflection in the vicinity of the p* value, which depends on the K
m/K
d ratio. Different methods for determining the p* value have been described. At low ratios between the conductivities of a dispersed phase and a dispersion medium, the inflection is very weakly pronounced. However, the representation of the K(p) dependences in semilog coordinated substantially facilitates its identification. PubDate: 20160301
Abstract: Abstract
Higherorder moments of particle size distribution functions are determined for magnetic fluids from analysis of initial segments of magnetization curves. It is shown that the higherorder moments calculated using approximation of real particle size distributions by the Γ distribution are strongly overestimated. Agreement between the measured and calculated moments can be radically improved by truncating maximum particle size X
max. A relation between X
max and the parameters of the Γ distribution is proposed taking into account the degree of polydispersity of a magnetic fluid. Namely, the ratio between the maximum and most probable particle diameters is equal to the ratio between the meansquare magnetic moment of a particle and its squared average magnetic moment. PubDate: 20160301
Abstract: Abstract
A complex study of electrosurface properties has been performed for singlecrystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and Xray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acidbase potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the Γ
H
+
(pH) and Γ
OH

(pH) adsorption isotherms of potentialdetermining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions. PubDate: 20160301