The interpolymer interaction in the lignosulfonate (LS)–chitosan (ChTS) system, in which ChTS is dissolved in aspartic acid (ChTS·Asp), has been studied, and the colloid-chemical regularities of macrophase separation accompanied by the formation of a water-insoluble polyelectrolyte complex (PEC) have been determined. The data on the concentration dependences of molar conductivity and pH have been used to show that LS and ChTS·Asp solutions exhibit polyelectrolyte properties. On the basis of the potentiometrically controlled dosed mixing of polyelectrolyte solutions in two different orders, the cloud points have been determined and an empirical phase state diagram has been plotted for the LS–ChTS·Asp systems. It has been found that, when the LS solution is added to the ChTS·Asp solution, the turbidity onset is observed at conditional analytical ratio n( SO_3^ - )/n( NH_3^ + ) = 0.015–0.567, i.e., in the region of an analytical excess of ChTS amino groups. At the reverse mixing order, when the ChTS·Asp solution is added to the LS solution, the initial turbidity is recorded at ratio n( SO_3^ - )/n( NH_3^ + ) = 6.30–7.03, which corresponds to an analytical excess of LS sulfonate groups. Hence, the transition of the system to the macrophase separation is not caused by the achievement of a conditional charge equivalence of the functional groups and essentially depends on the order of component addition, the local composition of the medium, and the concentration and kinetic factors. Water-insoluble PEC has been isolated from the LS–ChTS·Asp systems and characterized using FTIR spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Taken together, the obtained data indicate the formation of an LS–ChTS interpolymer complex with involvement of electrostatic interactions between SO_3^ - groups of LS and NH_3^ + groups of protonated ChTS, as well as hydrogen bonding. It has been found that the phase behavior of the system is governed not only by the charge ratio of the components, but also by the mixing order and the conformational and associative features of the natural polyelectrolytes in an aqueous medium.
This work examines the possibility of controlling biocatalytic reactions in self-organizing systems using cytochrome C as a catalyst. It is known that it can accelerate biological processes acting as a catalyst for cellular respiration. Microemulsions based on sodium bis(2-ethylhexyl)sulfosuccinate (AOT) are of significant interest as nanosized transport and reaction systems in biocatalysis, as they are capable of stabilizing enzymes while maintaining their functional activity. In this study, three-component water/AOT/isopropyl myristate systems with different compositions and degrees of hydration have been obtained. They have the structure of water-in-oil microemulsions with droplet sizes of 4.2–8.7 nm, as well as the structure of liquid crystals. The structure-related phase transformations in the systems under consideration have been studied upon increasing AOT concentration from microemulsions to a liquid crystalline mesophase. It has been found that the incorporation of cytochrome C into the microemulsions results in its good solubilization, which leads to a slight decrease in droplet sizes and their narrower distribution in the system. The UV–Vis and luminescence spectroscopy data have shown the occurrence of the adsorption interaction between the protein and the polar groups of AOT. The applicability of the obtained systems to biocatalysis has been investigated using the example of guaiacol oxidation with hydrogen peroxide in the presence of cytochrome C. To controllably increase the yield of the catalytic reaction product in the microemulsion, hydrophilic Cd0.9Mn0.1S/ZnS quantum dots stabilized with mercaptopropionic acid have been added to the microemulsion. It has been found that the yield of tetraguaiacol in the reaction increases in direct proportion to the concentration of the introduced quantum dots. Thus, the catalytic processes can be accelerated or slowed down using the microemulsions as reaction media.
A theory has been developed for nanodispersion of a simple liquid under the conditions of thermal evaporation in a supersaturated medium and ultrasonic cavitation. The proposed theory takes into account the size dependence of surface tension. It has been shown that accounting for this dependence decreases the energy barrier of nucleation and the critical nucleus radius, while causing a significant asymmetry in the kinetics of the growth and evaporation of nanodroplets. The modified Rayleigh–Plesset equation has been used to show that the size dependence of the surface tension increases the capillary stiffness of a bubble, suppresses chaotic regimes, and preserves the scale-invariant (fractal) structure of cavitation oscillations. A new criterion has been obtained for the disappearance of the nucleation barrier. It has been shown that, under real conditions of ultrasonic cavitation, the supersaturation reaches values sufficiently high for the transition to the spinodal regime of spontaneous phase separation and the formation of nanodroplets (1–3 nm in size) without an activation delay.
The electrostatic interaction of two identical charged dielectric spheroidal particles in a symmetric electrolyte solution has been considered. The finite element method has been used to calculate the repulsive forces between the particles by the Poisson–Boltzmann equation under the condition that their surface charge distribution is independent of the interparticle distance and there is no external electrostatic field. The charge distribution on the surface of each particle is assumed to coincide with that on an isolated individual particle at a given surface potential. It has been found that, depending on the Debye length and the distance between the particle surfaces, an increase in the longitudinal size of the particles upon the passage from oblate to prolate spheroids can either enhance or weaken the interaction force.
Quasi-stationary hydrodynamic flows have been studied in a small slowly evaporating hemispherical droplet with a pinned contact line on a flat horizontal substrate. Analytical solutions of the Stokes equations have been obtained and visualized for a capillary flow, which corresponds to the so-called “coffee-ring effect,” as well as for the Marangoni flow induced by a surface tension gradient associated with the cooling of the droplet surface due to the evaporation. The flow model corresponds to low Reynolds and Peclet numbers. The boundary conditions corresponding to the presence or absence of liquid slip at the substrate, which facilitate or hinder the Marangoni flow, have been analyzed. A hypothesis has been proposed that a critical Marangoni number corresponds to the system parameters that provide the separation of the flow from the substrate and the transition to the slip mode, in which the liquid velocity immediately at the substrate surface is nonzero. The obtained result can be used to study the flow structure and evaluate the flow rate in an evaporating microdroplet.
