Vol 78, No 1 (2016)

Isosteric heats of hydrogen, nitrogen, and methane adsorption on graphite surface have been calculated and analyzed using the density functional theory. The heats of adsorption have been calculated within wide ranges of pressures and subcritical temperatures. The peaks in the temperature dependences of isosteric heat of adsorption have been found to correlate with the degrees of filling of monolayers during adsorption.

Computer simulation has been employed to obtain equilibrium molecular configurations, as well as spatial and angular distributions of water molecules, under the action of the field of a single-charged chlorine anion in a model planar nanopore with structureless walls at room temperature. A detailed many-body model of intermolecular interactions calibrated in accordance with experimental data relative to the free energy of hydration in water vapor has been used. The effect of the hydrophilicity of the walls on the ion hydration shell consists in its disintegration into two parts, i.e., molecules retained exclusively due to the interactions with the ion and those adsorbed on the walls. In the regime of strong interactions with the walls, two relatively stable states arise with asymmetric distribution of molecules between opposite walls. The existence of the two metastable states destabilizes the position of ions inside a pore and is expected to accelerate their adsorption on the walls.

Herein, we report the study of the influence of ascorbic acid and temperature on the micellization of a cationic gemini surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide), 16-6-16. The critical micelle concentration (CMC) of 16-6-16 was measured by the conductivity method and dye solubilisation technique. A tendency of the CMC values to increase with temperature and upon the adding of ascorbic acid was found. The standard Gibbs energy, standard enthalpy, and standard entropy of micellization of 16-6-16 were evaluated. The results of calculations suggest the decrease of the stability of the 16-6-16 micellar solution in the presence of ascorbic acid.

Cadmium sulfide (CdS) nanoparticles have been obtained by chemical precipitation onto the surface of single-crystalline silicon from an aqueous solution of ammonia, cadmium chloride (CdCl₂), and thiourea, as well as from water–DMSO and water–DMF mixtures with the same concentrations of the reagents. According to data of atomic force microscopy, the samples obtained from the aqueous solution consist of individual nanoparticles and agglomerates thereof with sizes of no larger than 1 µm. Materials obtained from the water–organic mixtures are distinguished by the aggregation of CdS nanoparticles into threadlike chains. The length of the formed curved chains and the size of CdS nanoparticles composing them depend on the nature and amount of an organic component of a mixture. Atomic force microscopy, transmission electron microscopy, and photoluminescence spectroscopy data have shown that the average size of CdS nanoparticles is 2–2.5 nm depending on solvent composition.

A new approach to template synthesis of mesostructured pH-sensitive SiO₂ nanocontainers is developed. The approach combines the stages of synthesis of the nanocontainers and their loading with a targeted functional substance. The structure, capacity, and the rate of “unloading” of the nanocontainers at different pH values of an aqueous medium under static and quasi-dynamic conditions are studied using mesoporous SiO₂ nanoparticles as a model. Nanoparticles are synthesized using the micelles of cetyltrimethylammonium bromide as templates. Based on the obtained information, a mechanism is proposed for release of cetyltrimethylammonium cations from SiO₂ nanocontainers into the aqueous medium.

Methods for targeted regulation of the surface properties of polymer film materials (substrates) by fluorination and sulfonation have been considered. It has been shown by the examples of polyethylene, polypropylene, and poly(ethylene terephthalate) films that these methods can be used for the production of polymer films with controlled values of water contact angle from 20° to 88°, adhesion force from 23 to 141 rel. units, and surface roughness parameter R_a from 35 to 382 nm. This set of substrates may be used to optimize the methods for the formation of structured functional polymer surfaces. In particular, the regularities of the formation of solid deposits of colloidal submicron particles during evaporation of droplets of their solutions have been shown to vary with variations in substrate characteristics.

Complex macroporous poly(vinyl alcohol) (PVA) cryogels have been obtained by cryogenic treatment (freezing at–20°C for 12 h followed by defrosting at a rate of 0.03°C/min) of PVA–chitosan hydrochloride mixed solutions. The subsequent alkaline treatment of the cryogels has resulted in the transformation of the water-soluble salt form of chitosan into its insoluble basic form, which coagulates inside the bulk of the continuous phase of PVA cryogel into small particles with sizes of 2–5 µm. In the resulting composite cryogels, these particles play the role of an “active” filler, which increases the rigidity and heat endurance of the gel material. It has been shown that the sorption capacity of such chitosan particles entrapped into the bulk of composite cryogels with respect of bivalent copper ions is noticeably higher than the sorption capacity of ground chitosan particles incorporated as a discrete filler into the continuous phase PVA cryogels. The study of the properties of PVA–chitosan hydrochloride mixed solutions revealed that these polymers are, to a large extent, compatible with one another in a common solvent at a low ionic strength. Therefore, liquidliquid phase separation of these systems due to the thermodynamic incompatibility of macromolecules of different natures is observed only upon increasing the ionic strength by adding a low-molecular-mass salt (NaCl, 0.15 mol/L) to the solution.

The rheological behavior of slurries of coal at different stages of metamorphism has been studied as depending on glycerol content in an aqueous dispersion medium. Increased viscosity and reduced polarity of water–glycerol solutions have been found to increase the shear stress and viscosity of coal slurries. The effective viscosity of the slurries has been revealed to decline at the same weight content of the dispersed phase with a rise in the stage of coal metamorphism (i.e., when passing from brown coal to anthracite).

Contemporary interpretation of shear thickening and deformation (dynamic) glass transition phenomena in concentrated suspensions has been considered. The concentration limits that predetermine structuring resulting from volume effects, which control percolation and the randomly limiting volume filling, have been formulated. The former of them is responsible for the appearance of the yield point, while the latter determines the possibility of the dynamic glass transition, which leads to “jamming,” i.e., impossibility of a flow. Physicochemical interactions lead to the fact that the yield point may appear at dispersion phase concentrations many orders of magnitude lower than the percolation threshold, while the interactions and friction between dispersed phase particles result in the glass transition at concentrations lower than the randomly limiting volume filling. The contemporary ideas of the possibility or impossibility of the existence of the maximal Newtonian viscosity at stresses below the yield point and the concept of the kinetic (thixotropic) transition through the yield point have been discussed.