Vol 86, No 5 (2024)

A method has been developed for the formation of hybrid membranes consisting of a hydrophilic microporous substrate and a hydrophobic nanofiber polymer layer deposited by electroforming. A track-etched membrane made of polyethylene terephthalate was used as a hydrophilic microporous substrate, on the surface of which a thin layer of titanium was applied by magnetron sputtering to ensure adhesion of the nanofiber layer. Simultaneously, the titanium coating was used to make a conductive track-etched membrane that served as a collector electrode. It is been shown that the application of this method for the formation of polymer coatings when used as a starting material for the formation of polyvinylidene fluoride nanofibers makes it possible to obtain a layer with highly hydrophobic properties, the water contact angle of the surface of which, depending on the deposition density, averages 143.3 ± 1.3°. A study of the morphology of the nanofiber coating shows that it has a microstructure typical of non-woven materials. The nanofibers forming the porous system of this layer have a wide range in size. The study of the molecular structure of the nanofiber layer by IR-Fourier spectroscopy and X-ray diffraction analysis showed that its structure is dominated by the β-phase, which is characterized by a maximum dipole moment. It is been shown that the hybrid membranes of the developed sample provide high separation selectivity when desalting an aqueous solution of sodium chloride with a concentration of 26.5 g/l by membrane distillation. The salt rejection coefficient for membranes with a nanofiber layer density from 20.7 ± 0.2 to 27.6 ± 0.2 g/m² in the studied mode of the membrane distillation process is 99.97−99.98%. It has been established that the use of a highly hydrophobic nanofiber layer with a developed pore structure in combination with a hydrophilic microporous base makes it possible to increase the productivity of the membrane distillation process. The value of the maximum condensate flow through the membranes is on average 7.0 kg m²/h and its depends on the density of the deposited nanofiber layer.

On the basis of the Poisson-Boltzmann equation the electrostatic interaction between two charged dielectric spherical particles in a symmetric electrolyte solution is considered. The interaction forces between particles of the same radius under the condition of uniform charge distribution on their surfaces in the absence of an external field have been calculated by the finite element method. The dependence of the electrostatic repulsion forces between the particles on the magnitude of the particle charges and the dielectric permittivities of the particle materials and the surrounding medium has been analyzed.

New composite materials (ionogels) have been obtained based on imidazolium ionic liquids immobilized in highly porous polymers, i.e., polyamide 6,6 (nylon 6,6) and low-density polyethylene. A method has been proposed for determining the rate of ionic liquid removal from an ionogel upon contact with water, with this method being based on continuous measuring the conductivity of an aqueous phase. The results of the conductometric measurements have been confirmed by high-performance liquid chromatography data. It has been shown that the stability of ionogels upon contact with water is determined by both the hydrophobicity of a polymer matrix and the solubility of an ionic liquid in water. The highest degree of ionic liquid removal (more than 80%) has been observed for composites based on porous polyamide 6,6 (hydrophilic matrix) and dicyanimide 1-butyl-3-methylimidazolium (completely miscible with water). Ionogels based on lowdensity polyethylene (hydrophobic matrix) and bis(trifluoromethylsulfonyl)imide 1-butyl-3-methylimidazolium (poorly soluble, <1 wt %, in water) have shown the highest stability (washout degree of no more than 53% over 24 h). The method proposed for analyzing the rate of ionic liquid dissolution in water has been used to discuss the mechanism of this process.

In the last two decades, the creation and research of superhydrophobic nanomaterials based on the “lotus effect” have attracted great interest. The effect is caused by the heterogeneous wetting of rough surfaces, when the grooves of a rough surface are filled with air (vapour) and water only contacts the tops of the protrusions. The drop forms a sphere on the surface and, if slightly inclined, rolls down and picks up the dirt particles. A wide variety of methods have been developed to produce such materials, among which potential of the ion track technology (ITT) is being explored. The aim of this research was to investigate the wettability of surface microrelief using two materials with different initial hydrophobicity degrees. By modifying the surface of polycarbonate and polypropylene films using the ITT, the samples with water contact angles of 140 ± 5° and 151 ± 5° at maximum, respectively, were obtained. It is shown that such angles are characteristic of microrelief, where the fraction f of the surface that is in contact with the droplet is decreased to the range 0 < f < 0.3. In order to increase the probability of droplets rolling down the material surface in a certain direction, the materials with inclined microrelief were obtained. In this case, the wettability becomes anisotropic. The droplet loses its spherical shape, deforming in the direction of inclination of needle-like surface elements. It was found that the anisotropy of wettability is higher at an inclination angle of the relief elements of 45° than that at 30° (relative to the flat surface).

The self-cleaning effect of titanium dioxide coatings is based on the photocatalytic oxidizing ability and the effect of photoinduced superhydrophilicity. Metal doping is used to enhance photocatalytic activity, while its effect on surface hydrophilicity is practically not studied. In this work, the influence of heterovalent doping of anatase titanium dioxide on its hydrophilic properties was investigated in detail. Thin films x-M-TiO₂, where M – Nb⁵⁺, Sc³⁺, Al³⁺, with dopant concentration in the range of 0.0–1.0 at. %, were obtained on glass substrates from solutions of the corresponding sols by dip-coating method. The phase composition, surface dopant content, lattice microstress, surface acidity and electron work function values were determined and analyzed for three series of doped samples as a function of dopant concentration. The surface hydrophilicity of x-M-TiO₂ nanocoatings was evaluated using the water contact angle and surface free energy values. It was shown that doping with niobium ions changes the wettability of titanium dioxide, while its hydrophilic state does not change when doped with scandium and aluminum ions. It was found that the appearance of niobium ions in anatase leads to a sharp increase in the hydrophilicity of the surface with a simultaneous change in the acidity and work function, but with increasing Nb content the electronic factor becomes dominant. The obtained kinetic dependences of the photoinduced water contact angle showed an increase in the surface hydrophilicity of all investigated coatings irrespective of the dopant type within the given concentrations, which demonstrates their self-cleaning ability. At the same time, the final UV-induced hydrophilic state depends on the dopant type. Maximum surface hydrophilicity is achieved with UV irradiation of Nb-doped TiO₂ regardless of its content, the Al-doped series of coatings exhibit small contact angles, and the photoinduced surface hydrophilicity of Sc-doped titanium dioxide films decreases with increasing scandium content. Maximum surface hydrophilicity was achieved with UV irradiation of Nb-doped TiO₂ regardless of its content, the Al-doped series of coatings exhibit small water contact angle values, and the photoinduced surface hydrophilicity of Sc-doped titanium dioxide films decreases with increasing scandium content.

The kinetic dependences of surface tension, dilatational dynamic surface elasticity and ellipsometric angles of solutions of copolymers of styrene and 4-vinylbenzyl chloride modified with N,N-dimethyldodecylamine, as well as the micromophology of adsorption and spread layers of this polyelectrolyte were determined. All kinetic dependences of the dynamic surface elasticity were found to be monotonic, in contrast to the results for previously studied polyelectrolyte solutions without polystyrene fragments. The peculiarities of surface properties of the studied solutions may be related to the formation of microaggregates in the surface layer, preventing the formation of loops and tails of polymer chains at the interfacial boundary, and, consequently, the decrease in surface elasticity after the local maximum. The occurrence of aggregates with sizes of 1–4 nm in the Z-direction in the surface layer is also indicated by atomic force microscopy data. The obtained results confirm the earlier conclusions about the formation of aggregates in the surface layer of polyelectrolyte solutions containing sodium polystyrene sulfonate (PSS) fragments. A two-dimensional phase transition to a denser surface phase at surface pressures of 25–30 mN/m and the formation of aggregates with a size of 40 nm in the Z-direction were found for applied polyelectrolyte layers without styrene monomers on an aqueous substrate.