Polina S. Kazaryan

Expanded polystyrene (EPS) is costly to reprocess, occupies substantial landfill space, and presents significant challenges for reuse. The development of innovative methods for EPS recycling is therefore a promising area of research. This study explores the possibility of fabricating a dense foamed matrix from EPS and using it to produce strong acid cation (SAC) exchange resins for water purification. As an alternative to dissolution-based recycling, we propose a physical, environmentally friendly method involving the saturation of the pristine EPS matrix with CO₂ and its mixtures (modifying agents) under pressure. This approach enables the formation of a dense porous system while eliminating the need for subsequent solvent removal and cleaning. The modified EPS demonstrates a several-fold increase in density compared to the initial material and an SSA = 50–60 m²/g according to CO₂ sorption measurements. The ability to tailor pore size and density simply by varying the modifying agent, pressure, and exposure time was investigated. Structural analysis via SEM as well as N₂ and CO₂ sorption measurements revealed that the modification process critically dictates the pore architecture: treatment with pure CO₂ and a CO₂ + H₂ mixture resulted in the formation of meso- and macropores while preserving the presence of micropores in the material. FTIR spectroscopy and EDS analysis were employed to study the sulfonation of EPS and its resulting cation-exchange capacity. The kinetics of cations’ sorption was studied using capillary electrophoresis, and the static equilibrium ion exchange capacities were determined for both unmodified sulfonated EPS and modified sulfonated EPS towards Na⁺ and Ca²⁺ ions at various salinities of the model solutions. The resulting resins exhibited high sorption capacities, achieving 0.7–1.4 eq L⁻¹ for Na⁺ and 0.3–1.0 eq L⁻¹ for Ca²⁺ ions, while the sulfonated sample treated with the CO₂ + H₂ mixture exhibited the highest equilibrium capacity. The proposed methodology is relevant to both water purification and plastic waste recycling.

In this paper we study in detail the products formed during the process of water-assisted thermal oxidative decomposition (TOD) of polypropylene in the presence of pressurized oxygen. A set of techniques has shown that the main decomposition product in such a process is acetic acid with small amounts of other carboxylic acids (formic, propionic, succinic). The kinetics of carboxylic acid formation is studied by means of gas chromatography–mass-spectrometry as well as capillary electrophoresis, and the possible mechanisms behind the products formation are discussed. The role of water is considered based on the results obtained from substituting H₂O with D₂O in TOD. Compositions of residual oligomeric fractions as well as gas products are analyzed.

Omniphobic coatings effectively repelling water, oils, and other liquids are of great interest and have a broad number of applications including self-cleaning, anti-icing surfaces, biofouling protection, selective filtration, etc. To create such coatings, one should minimize the pinning force that resists droplet motion and causes contact angle hysteresis. The minimization of the free surface energy by means of the chemical modification of the solid surface is not enough to obtain a nonsticky slippery omniphobic surface. One should minimize the contact between the solid and the droplet. Besides coating the surface with flat polymer films, among the major approaches to create omniphobic coatings, one can reveal "lotus effect" textured coatings, slippery liquid-infused porous surfaces (SLIPS), and slippery omniphobic covalently attached liquid (SOCAL) coatings. It is possible to turn one surface type into other by texturizing, impregnating with liquids, or grafting flexible liquid-like polymer chains. There are a number of models describing the pinning force on surfaces, but the transitions between states with different wetting regimes remain poorly understood. At the same time, such studies can significantly broaden existing ideas about the physics of wetting, help to design coatings, and also contribute to the development of generalized models of the pinning force. Here we review the existing pinning force (contact angle hysteresis) models on various omniphobic substrates. Also, we discuss the current studies of the pinning force in the transitions between different wetting regimes.

In modern life, people face a wide number of sticky problems when adhesion is highly undesirable: water and dirt stick to clothes, useful materials stick to the walls of their containers and cannot be fully used, water sticking and freezing on airplane wings affects handling and can be dangerous, biological liquids can stick and form clots inside medical devices threatening patients' lives, etc. Slippery liquid-infused porous surfaces (SLIPSs) with pressure stable omniphobicity could help to solve these issues. Lubricant depletion from porous surface and subsequent degradation of omniphobic properties is the major problem for SLIPS. It could be resolved by attaching flexible, liquid-like sidechains to the polymer matrix. Understanding the relationship between the structure of such polymer films and wetting effects is therefore of great importance. The present work is devoted to the study of droplet pinning on crosslinked polydimethylsiloxane (PDMS) polymer films with varied amounts of attached flexible PDMS sidechains and clarification of the relationship between slippery and viscoelastic properties of the films. An one-stage approach to the synthesis of such slippery coatings on smooth and porous substrates in "eco-friendly" pressurized CO₂ solutions is proposed. Pinning force and Young's modulus (E) of the films on silicon substrates with variation of the grafted sidechains amount (x) are measured. The non-monotonic dependence of the pinning force on the amount of sidechains is obtained: the pinning force decreases at small x values (region I) and starts to increase at higher x (region II). The effects of the grafted sidechains amount, as well as matrix softening, are discussed for each case. It is demonstrated that the proposed method of film synthesis allows one to obtain thin, uniform coatings on fabrics without gluing the fibers. Such coatings with an optimal amount of PDMS sidechains demonstrate decreased sliding angles for droplets of water and aqueous alcohol solutions, as compared to PDMS coatings without grafted sidechains. The proposed technique may be of interest for deposition of coatings on porous surfaces having a complex morphology, such as textiles, aerogels, porous electrodes, etc.

We observed and studied the phenomenon of the redox front propagation in different polyaniline (PAni) deposited samples interfaced with liquid or solid polymeric electrolyte. The front of electrochemical conversion, in which the insulator and the conductor parts of PAni are interfaced, is studied observing the temporal evolution of the conductivity of PAni samples. The propagation of redox front was studied in electrochemically obtained thick (2 µm) and in thin (50 nm) poly-aniline films, obtained using Langmuir-Blodgett (LB) method. In the configuration that we tested, the speed of the red-ox front propagation for the thin LB films was found to be 200 micron/sec opening the way for the manufacturing large neural networks, realized using PAni based memristive devices, in which the memristance can be quickly changed in the programmable manner. The prototypes of the spiking neuron connections were manufactured on the basis of lithographically developed gold contacts, bridged by electrochemically grown polyaniline and placed under polymer electrolyte layer with only one counter electrode (gate) for the whole manifold of pseudo-two-terminal memristor bridges. The spike propagation was studied in such gold-polyaniline systems. The research opens the possibility of miniature spike or rate-based neural network circuits manufacture, based on metal pads and polyaniline.

The change in the pinning force during the transition from dry to oil-impregnated thin polymer films is studied for droplets of water and hexadecane. A careful variation of the oil amount in the films is performed by means of supercritical impregnation. The film thickness dependence on the oil content is measured using ellipsometry and compared to gel swelling theory estimates. Depending on the oil content, two cases of pinning force behavior have been identified. For each case, the factors that determine the pinning force are discussed. The pinning force in the transition from dry to equilibrium swollen gel films is well approximated by the Joanny and de Gennes hysteresis model of dilute defects.

The study addresses the relationship between the omniphobic properties of coatings based on polymer matrices doped with liquid lubricants (Slippery Liquid-Infused Porous Surfaces, SLIPS) and the degree of swelling of the matrices in the lubricant. A method for fabrication of matrices based on poly(perfluoroalkyl methacrylates) impregnated with fluorinated oils with different lubricant contents by one-stage synthesis in supercritical (SC) CO₂ is proposed. The dependence of the contact angle hysteresis and the sliding angle on the degree of swelling was studied for water and saturated hydrocarbon droplets. The lubricant content in the matrices was determined by thermogravimetric analysis and ellipsometry.