Vol 80, No 2 (2018)

Theoretical results published in the last 17 years on the kinetics of aggregation and relaxation in micellar surfactant solutions have been reviewed. The results obtained by the analytical and direct numerical solution of the Becker–Döring kinetic equations and the Smoluchowski generalized equations, which describe different possible mechanisms of aggregation and relaxation on all time scales from ultrafast relaxation while reaching the quasi-equilibrium in the region of subcritical molecular aggregates to the last stage of slow relaxation of micelles to the final aggregated state, have been considered in detail. The droplet model and the model linear with respect to aggregation numbers have been used for the work of aggregation to describe the dynamics of the rearrangement of micellar systems consisting of only spherical, only cylindrical, and coexisting spherical and cylindrical aggregates, with the dynamics being both linear and nonlinear with respect to deviations from equilibrium. The results of molecular simulation of the rearrangement kinetics of micellar systems subjected to initial disturbance have been reviewed.

The effect of borohydride concentration on the synthesis of gold nanoparticles in solutions of chloroauric acid, cetyltrimethylammonium bromide, and ascorbic acid in the absence of seeds has been studied systematically. Variations in the concentration of NaBH₄ allow one to obtain particles of different sizes and shapes. A method has been developed for the one-stage synthesis of large pentagonal gold rods (the average length and thickness are 550 ± 135 and 71.2 ± 11.6 nm, respectively) with a high yield using borohydride in an ultra-low (≤5 × 10^–8 mol/L) concentration. The resulting particles have been characterized using optical spectroscopy, scanning and transmission electron microscopy (including high-resolution technique), and electron diffraction.

The effect of temperature (23–58°C) on the structure and conductivity of thin films obtained by the moving meniscus method from nanodispersions of silver particles with sizes of 6.5–70 nm has been studied. It has been shown that an increase in temperature leads to an exponential decrease in the specific conductivity of the films, with their thickness varying nonmonotonically. In the case of “large” particles, an increase in temperature decreases the efficiency of their deposition onto a substrate. The reasons for the observed regularities have been discussed.

The equilibrium nucleus-size distribution determined by the method of statistical physics has been analyzed. The analysis has shown that nuclei composed of 1000 or fewer molecules are microscopic objects. They are described by partition functions and cannot be described by thermodynamic methods. An approach has been proposed that makes it possible to determine a partition function over internal degrees of freedom of a nucleus and express the aforementioned distribution via commonly accepted thermodynamic parameters. The solution of the problem is reduced to the determination of the evaporation rate of clusters by extrapolating the evaporation rate, which has been calculated for a macroscopic droplet of an incompressible liquid in terms of thermodynamic concepts with allowance for fluctuations, to the sizes of nuclei. As a result, a theory has been formulated for homogeneous stationary nucleation. The comparison of the proposed theory with experimental data has shown that the calculated sizes of critical nuclei coincide with the measured ones and that the theoretical nucleation rates either coincide with the measured rates or agree with them within one or two decimal orders of magnitude.

The electrophoretic motion of a polyelectrolyte capsule has been considered in a uniform electric field. The capsule carries a uniformly distributed charge and is permeable to ions of different natures. An electrolyte identical to a dispersion medium is located inside the capsule. The flow in the porous layer of the capsule has been described by the Brinkman equations taking into account the effect of electrostatic forces. The distribution of ions in the vicinity of the capsule has been determined, and its electrophoretic mobility has been found in a linear approximation. The mobility of the capsule has been studied as depending on its geometric characteristics, permeability, and charge density. In particular, a complex extremal character of variations in the mobility as depending on the solid phase fraction in the capsule has been revealed at different ratios between the thicknesses of the electrical double layer and the Brinkman filtration layer.

Mathematical simulation has been employed to study the permeability of a bilayer membrane taking into account finite rates of adsorption on the external surfaces of the membrane and internal diffusion in it. Analytical expressions are derived for transmembrane gas flux and permeability of the membrane. It has been revealed that the permeability may depend on the direction of gas flux (asymmetry effect). It has been shown that the asymmetry effect arises at different values of the parameters of the isotherms of gas sorption in membrane layers at a finite gas pressure. The main characteristics that govern the degree of asymmetry have been determined and analyzed. The rate of adsorption has been found to substantially influence the magnitude of the asymmetry effect in the bilayer membrane. It has been found that a two-layer membrane can function as a diffusion "diode", if adsorption is the limiting stage of gas transfer.

In the condensation mechanism of heterogeneous ice formation, water crystallization occurs after a necessary amount of the liquid phase has accumulated on a substrate surface. In this way, the ice-forming activity of the surface is governed by its adsorption ability with respect to water vapor. The Monte Carlo canonical statistical ensemble method has been used to calculate the free energy, entropy, and work of nucleation of a disordered condensed water phase on the surface of crystalline silver iodide and to determine the surface tension. Comparative calculations have been performed at 260 and 320 K for the defect-free surface of a basal face of a crystal. The surface of a β-AgI crystal is completely covered with a monomolecular film even in unsaturated water vapors. The surface tension at the growing nucleus–substrate interface substantially increases due to the formation of the underlying film, and the growth of the nucleus becomes possible only in a supersaturated vapor. As the vapor density increases, the thickness of the condensed water layer grows, and, at negative Celsius temperatures, conditions are created for its crystallization. The underlying film with pronounced hydrophobic properties hinders nucleation, thereby decreasing the ice-forming activity of the surface in the condensation process. Under these conditions, the observed abnormally high ice-forming activity of silver-iodide aerosol particles may be explained by the presence of numerous crystal defects on the particle surface, with these defects representing channels that provide overcoming the hindering action of the film.