Vol 80, No 3 (2018)

The Becker–Döring kinetic equations are employed to describe the stage of ultrafast relaxation in micellar surfactant solutions, which ends in the establishment of a quasi-equilibrium distribution in the premicellar region of aggregate sizes. This is performed by analyzing the spectrum of the eigenvalues of the matrix of kinetic coefficients of the linearized Becker–Döring difference equations, which describes the complete multistage relaxation in a micellar system. The first value of the spectrum ordered as an ascending series is equal to zero (infinite relaxation time), thereby corresponding to the law of conservation of the surfactant quantity. The second value is very small; it differs from the series of subsequent values by several orders of magnitude and determines the time of slow relaxation. The other eigenvalues describe the processes of fast relaxation and comprise the contributions from the relaxation processes in both micellar and premicellar regions of aggregate sizes. In the latter region of the spectrum, the contribution of the ultrafast relaxation can be numerically distinguished. The obtained result is confirmed by the analysis of the spectrum of relaxation times of premicellar aggregates, which are considered as a closed system. It is also shown that the spectrum of ultrafast relaxation times is mainly determined by the first diagonal elements of the matrix of the linearized Becker–Döring equations and can be described analytically.

The structural (structural resistance coefficient, bulk porosity, average pore radius, and specific surface area) and electrokinetic (surface conductivity and electrokinetic potential) characteristics of high-silica micro- and macroporous glasses produced from two-phase sodium borosilicate glass have been compared in solutions of an indifferent electrolyte (sodium chloride) and iron(III) chloride containing iron ions, which have a high specificity to silica surfaces. It has been shown that, in the presence of iron ions, the electrokinetic behavior of porous glasses is governed by two factors. First, the superequivalent adsorption of these ions in the Stern layer leads to positive values of the electrokinetic potential, and, second, their mobility in the pore space decreases, thereby resulting in the appearance of equilibrium solution concentration ranges, in which the specific conductivity of a pore solution becomes lower than that of a free solution.

The porosity of polymer materials produced by polymerizing dispersion media of highly concentrated emulsions may be predicted, provided that the emulsions are stable. The study of the stability of water-in-oil (W/O) emulsions containing styrene as a dispersion medium at 25 and 65°C has shown that emulsions with a dispersed phase fraction of 0.75 and sorbitan monooleate concentrations of 1.5–20.0 vol % are stable to coalescence but are unstable to sedimentation. Emulsions with a dispersed phase fraction of 0.95 are stable to both coalescence and sedimentation at sorbitan monooleate concentrations of 10–20 vol %. Open-pore polymer materials are formed from emulsions with dispersed phase fractions of 0.75 and 0.95 at sorbitan monooleate concentrations of 2.0–3.5 and 10–12 vol %, respectively. At a dispersed phase fraction of 0.75 and a sorbitan monooleate concentration of <2 vol %, a multiple O/W/O emulsion is formed, the polymerization of which yields a porous polymer material containing spherical polystyrene particles inside pores. At higher surfactant concentrations in emulsions with dispersed phase fractions of 0.75 and 0.95 partly destroyed porous materials are formed.

Dynamic light scattering, conductometry, and capillary viscometry have been used to study aqueous micellar solutions of dodecyl-, tetradecyl-, and hexadecyltriphenylphosphonium bromides in a wide range of concentrations covering the first and second critical micelle concentrations (CMC₁ and CMC₂). It has been shown that the concentration curves for the diffusion coefficients of the ionic surfactants increase above CMC₁ and, then, pass through a maximum. As the alkyl chain length increases, the slopes of the concentration curves within the range of the linear growth in the diffusion coefficient rise, the height of the maximum increases, and its position shifts toward lower concentrations. The obtained results have been explained in terms of a theory previously developed for ideal micellar systems. It has been shown that the mobility factor plays the predominant role in the range of the linear increase in the diffusion coefficient and the effect of the viscosity of a micellar surfactant solution is enhanced with a rise in its concentration.

Oligohexamet diglycidyl ether hyleneguanidine (OHMG) stearates and palmitates, which have a higher solubility in epoxy oligomers (EOs) (glycidyl ethers of diphenylolpropane, Epikote 828, and polyglycidyle ether of oligooxypropilene oligooxypropylene polyol, Laproksid 703) than the widely used OHMG hydrochloride has, have been synthesized and characterized. Probably due to the better solubility, pronounced chemical interaction between EOs and OHMG fatty-acid salts occurs to yield adducts of EOs and OHMG, which are completely compatible with an initial EO. It has been proposed to incorporate OHMG fatty-acid salts into epoxy-amine networks via the preliminary synthesis of EO–OHMG adducts.

The regions of stability and coagulation of hydrosols of oxidized detonation nanodiamonds in the presence of inorganic salts and surfactants of different types have been determined. Concentration C_c of inorganic salts corresponding to the onset of the growth of aggregates in a hydrosol dramatically decreases with an increase in coagulating ion charge z: C_c ~ z^−5.3. Anionic and nonionic surfactants stabilize dispersions of nanodiamonds, while additives of cationic and zwitterionic surfactants cause coagulation. The study of the coagulating effect of alkylpyridinium chlorides has shown that the coagulation threshold halves upon elongation of the hydrocarbon chain in a surfactant molecule by a СН₂ group.

The effect of the polydispersity of fibrous materials on the viscous drag and the efficiency of gas filtration has been studied. The dependence of the Brinkman constant on parameter β_g, which characterizes the variance of the lognormal function of fiber-length distribution over fiber radii, has been calculated for equations describing the hydrodynamics of a gas in a porous medium. The dependences of the effective aerosol- particle-collection efficiency on the packing density, dispersion of fiber-size scatter, and average fiber radius have been investigated. Quality parameters of filters with different degrees of polydispersity have been compared. Results of calculations have been compared with experimental data.

It has been shown for the first time that nanosized organosilica toroids can be formed via hydrolytic condensation of (γ-mercaptopropyl)trimethoxysilane in an alkaline medium. It has been found that such toroids may be used as “nuclei” for the synthesis of plasmonic composite nanoparticles with a core/shell structure.