Vol 81, No 2 (2019)

Hamaker’s classical approach has been used to derive relations for the energy and force of the interaction between nanoparticles with different shapes and a planar solid surface. The shapes have been represented by a sphere (the model of an isometric particle), a cylindrical disk (the model of a platelike particle), and a cylindrical rod (the model of a rodlike particle). Energy- and force-related shape factors, which are special coefficients characterizing the effect of particle shape on the intensity of particle interaction with a macroscopic solid, have been introduced and calculated. Functions of two types have been analyzed for the shape factors, i.e., the dependence on the gap between a particle and a solid and the dependence on the distance from the mass center of a particle to the surface of the solid. All calculations have been performed using the pair potential of dispersion forces without retardation.

Inertial deposition of high-density submicron particles in high-performance filters consisting of submicron fibers has been studied. It has been experimentally found that the particles are completely collected by the filters at Stokes numbers substantially exceeding the critical numbers, above which the rebound of the particles from the fibers may take place. It has been assumed that the recorded penetration of radioactivity through analytical high-performance filters in the course of sampling air containing submicron particles of nuclear fuel is due to the penetration of nanoparticles, i.e., so-called “alpha-recoil aggregates” that result from the self-sputtering of α-active materials.

Molecular dynamics has been employed to study conformational changes of polyampholytic polypeptides on the surface of a spherical gold nanoparticle at different surface charge densities, including the case of the presence of eosin Y anions adsorbed on polypeptide macrochains. Equilibrium conformations have been determined for polyampholytic polypeptides adsorbed of a spherical gold nanoparticle. Radial distributions of the concentration of atoms of polyampholytic polypeptides on the gold nanoparticle have been plotted with differentiation over the types of units at different surface charge densities. Corresponding distributions have also been obtained for dye anions adsorbed on polypeptide macrochains. The results obtained may be used for the development and modification of sensors with tunable conformational structures of macrochains, such as luminescent optical testers for the concentration of molecular oxygen (including singlet oxygen) and chemical sensors based on the effects of surface plasmon resonance and surface-enhanced Raman scattering.

A theoretical model describing experimental data on the electrophoretic mobility of liposomes, which are formed from mixtures of charged (cardiolipin) and neutral (phosphatidylcholine) lipids and contain polylysine molecules adsorbed on them, is considered. The experimental data show that the ζ potential of the liposomes depends on the concentration of the adsorbed polylysine. The proposed model is used to determine the physically measured characteristics describing the system: the thickness of the adsorbed polymer layer, the surface area fraction occupied by the polymer at saturation, and the polymer–liposome surface binding constant. The performed calculations show that the reversibility of the adsorption dramatically decreases with an increase in the sizes of adsorbed polymer molecules. In addition, the presented model explains the behavior of the point of zero charge upon variations in the system parameters. The considered model is not confined to a specific type of polymers and phospholipids and may be used to study the adsorption of other biologically significant synthetic polycations and polypeptides.

The modification of polymer surfaces with fluorine–oxygen mixtures has been studied with wide variations in the process duration and percentage ratio between these gases in the mixture. The modification increases the hydrophilicity of the polymer surface, and, the higher the fraction of oxygen in the gas mixture and the longer the oxyfluorination time, the greater the increase in the hydrophilicity. The physicochemical properties of polymers, such as wettability, surface energy, and adhesion, may be regulated within rather wide ranges by varying oxyfluorination conditions. For example, in the case of polyolefins, the water contact angle changes from 78°‒87° for initial polymers to 49°‒60° for modified ones. For heterochain polymers, this range may be even wider and is for, e.g., poly(ethylene terephthalate) from 67° to 4°; i.e. almost complete water spreading over the polymer surface is achieved. The contribution of the polymer surface roughness to the observed values of the water contact angle has been determined before and after the chemical treatment. It has been shown that an increase in the wettability of the polymer surface as a result of oxyfluorination may be used to obtain polymer films capable of altering their wettability under subsequent tensile deformation.

The compatibility of tetraethoxysilane (TEOS) with polyacrylonitrile (PAN) solutions in dimethyl sulfoxide, the morphology of the mixed systems, and their rheological behavior have been analyzed. The combination of interferometry, refractometry, and optical microscopy has been employed to study the phase equilibrium realized in mixtures of TEOS with dimethyl sulfoxide and a PAN solution and to plot phase diagrams, which have indicated that TEOS is soluble in the PAN solution up to TEOS concentrations of 10–11%. As the TEOS content is increased within a concentration range of 10–20%, an emulsion with droplet sizes up to 40 µm is formed. At higher TEOS concentrations, the macroscopic separation of the system takes place. It has been shown with the use of rotational rheometry that, in the range of solutions, the presence of TEOS leads to a decrease in their viscosity and elasticity, while the viscosity increases in the range of emulsification. The analysis of the dynamic data has, for the first time, shown the bifurcation of the dependences of the storage modulus on the loss modulus at the point of phase separation. The calculation of the characteristic relaxation time of the ternary system and the dependence of this time on TEOS concentration has indicated a dramatic growth of the relaxation time in the region of emulsification, with this growth being determined by the relaxation properties of interfaces. Considering the obtained systems as a raw material for producing composite fibers, a solution droplet has been used to simulate the effect of TEOS on the kinetics of coagulation of PAN solutions with precipitants having different activities. It has been shown that, depending on TEOS concentration, the precipitation may yield gels with the content of this organosilicon additive either uniformly or nonuniformly distributed over the hypothetic cross section of a fiber.

The unidimensional diffusion transfer of a gas through a medium composed of two dissimilar layers has been studied. The heterogeneity of the layers was simulated by the dependences of diffusion coefficients on a spatial variable. Analytical expressions have been derived for the flux of a substance that diffuses through the medium at arbitrary dependences of the diffusion coefficients on the spatial variable. A generalized relation has been obtained for the permeability of the two-layer heterogeneous membrane. It has been found that the permeability of such a membrane may depend on the direction of the transfer. Mathematical simulation has been carried out for the transfer in the case of an exponential dependence of the diffusion coefficients on the spatial variable. The main parameters affecting the asymmetry of the transfer have been determined. It has been shown that the asymmetry effect may arise, provided that at least one of the diffusion coefficients depends on the spatial variable. It has been found that, at some values of the membrane heterogeneity parameters, the gas transfer occurs in the regime of a “diffused diode.”

A model developed for the description of experimental data on heterogeneous nucleation in disperse systems with metastable dispersed phases is applied to the case of ice nucleation in a water emulsion in decane under methane pressure . Activity spectra are obtained for ice-forming particles in the water–decane–methane system. The frequency of ice nucleation on these particles is calculated. Activities of ice- and clathrate-forming particles in this system are compared. It is shown that small amounts of active particles incorporated into the system from an environment can have a significant effect on ice nucleation.