Vol 85, No 3 (2023)

One of the most actively developing research areas in materials science relevant to polyfunctional coatings is the creation of slippery liquid-infused porous surfaces (SLIPS) based on porous hydrophobic or hydrophilic materials filled with low-volatility viscous liquids (lubricants). In the present work, we have investigated the possibility of using two organosilicon liquids of different polarities, bis(trifluoromethylsulfonyl)imide dicationic ionic liquid and silicone oil, as lubricants for fabricating slippery coatings that reduce the adhesion of solid and liquid aqueous precipitations to aluminium oxide substrates. To calculate the stability of the films of such lubricants, we have employed the theory of van der Waals forces to study the refractive index dispersions and the dielectric properties of the liquids in the region of microwave relaxation. On the basis of experimentally obtained data, the dielectric permittivity spectra have been calculated as functions of imaginary frequency for the entire spectral range, as well as the contribution of the van der Waals forces to the stability of the disjoining pressure isotherms of the lubricant films on the hydrophobic and hydrophilic aluminium oxide substrates. The disjoining pressure isotherms obtained in this work have indicated that the ionic liquid used to prepare slippery coatings is a more durable lubricant than silicone oil, because its films retain their stability when the vapor phase is replaced by an aqueous medium over a wider range of thickness.

Nanoemulsions (NEs) of simple compositions have been obtained, in which polyoxyethylene(4) lauryl ether (Brij L4, Br-4) plays the roles of a dispersed phase and a stabilizer, while water is a dispersion medium. The following properties of NEs have been studied: particle size distribution; solubilization capacity; and transport properties with respect to the lipophilic biocide, chlorhexidine (CH) base. The long-term aggregative stability of NEs (for several months) and the efficient mass transfer of CH by the NE dispersed phase particles in the aqueous medium have been confirmed. A unique phenomenon of a spontaneous decrease in the sizes of NE droplets upon solubilization of CH has been found, with the particle average diameter decreasing from 52 ± 6 to 19 ± 3 nm. The reason for this phenomenon is the formation of complexes between Br-4 and CH molecules on the surface of the droplets, with the complexes being better soluble in water than Br-4. Brij L4 molecules included into the complexes are transferred from the droplet surface into the dispersion medium, thus leading to the decrease in the droplet sizes. The complexation occurs due to the formation of multiple N⋅⋅⋅H⋅⋅⋅O hydrogen bonds. From 84 to 96% of the biocide solubilized in the NEs is also localized in the polyoxyethylated layer of Br-4 droplets due to H-bonds.

The interaction of iron oxide nanoparticles with an aqueous medium has been studied. The composition of the nanoparticles corresponds to magnetite–maghemite solid solutions with different Fe2+/Fe3+ ratios. Nanoparticles that most closely correspond to the composition of maghemite (γ-Fe2O3) have largest hydrodynamic diameters and cause a drastic decrease in the pH of the dispersion medium during the dispersion of the powders in water. Nanoparticles that have a phase composition of a solid solution corresponding to the middle of the magnetite–maghemite series are characterized by a gradual and less pronounced decrease in pH. It has been shown that dilution of aqueous suspensions obtained from preliminarily dried powders within a concentration range of 100–0.001 mg/L followed by sonication leads to a significant increase in the hydrodynamic diameter of iron oxide particles. A possible mechanism of the studied interaction of nanoparticles with the aqueous medium has been considered. This mechanism comprises the hydration of Lewis acid sites formed by iron ions and changes in the character of the dissociation of hydroxyl groups depending on the pH of a suspension. The effect of surface passivation of the studied nanopowders with oleic acid on the processes under consideration has been investigated. The results obtained make it possible to predict the aggregative stability and a number of other characteristics of the studied suspensions being diluted with water.

The rheological behavior of 1 wt % suspensions of micro- and nanocellulose in olive oil is studied at various electric field strengths up to 7 kV/mm. The particle morphology is evaluated by optical and electron microscopy. Under an electric field, a contrast transition from a simply viscous behavior of fluids to a visco-elastic one is observed, while the suspensions show yield stress and storage modulus. A higher electrorheological response of suspensions filled with nanocellulose compared to microcellulose has been established. Based on the dependences of the static yield stress on the electric field strength, an analysis of the mechanism of the electrorheological effect has been provided. The use of completely natural components has shown promise of developing novel, environmentally friendly “smart” materials.

Fibrin is formed via polymerization of one of the main blood proteins, fibrinogen, under the action of an enzyme, thrombin. Dynamic surface elasticity and dynamic surface tension of mixed solutions of fibrinogen and thrombin are measured as functions of surface age and enzyme concentration (50–800 U/L). The nonmonotonic pattern of the dependences for the dynamic surface elasticity indicates the multistage character of fibrin film formation and makes it possible to monitor the transition from unfolded protein to individual filamentous aggregates; a network of branched fibrils; and, finally, a continuous film. The dynamic surface elasticity of fibrin films is twofold higher than the corresponding values for fibrinogen (115 and 55 mN/m, respectively). The use of different types of microscopy makes it possible to assess the morphology of the obtained films.

The development of a simple and reproducible method for the synthesis of monodisperse silica particles is of considerable interest from the point of view of their numerous applications in photonics, biosensing, and biomedicine. When using the well-known Stober method, there is a continuous formation and growth of seeds, which leads to the synthesis of polydisperse colloids. In this work, we used the method of successive growth of silica particles obtained by hydrolytic condensation of tetraethylorthosilicate in an alcoholic-aqueous medium using an alkaline catalyst. It is shown that this technique makes it possible to obtain colloids with a particle size from 50 nm to 3 μm and a standard deviation of less than 5%. An additional advantage of the developed method of stepwise growth is the possibility to include fluorophores and SERS tags into the silica matrix.