Коллоидный журнал

Замораживанием при −20°С в течение 12 ч растворов поливинилового спирта (ПВС) с концентрацией полимера 100 г/л в воде или в диметилсульфоксиде (ДМСО) и далее оттаиванием при нагревании образцов со скоростью 0.03°С/мин сформированы нековалентные криогели ПВС (КГПВС), которые затем инкубировались в среде смесей Н₂О/ДМСО с разным их объемным соотношением. Методом диэлектрической спектрометрии определены значения диэлектрической проницаемости этих смешанных растворителей, характеризующей их полярность. Для обработанных такими смесями образцов КГПВС оценены изменения (по сравнению с исходными криогелями) объема, модуля упругости и теплофизические параметры их плавления. Показано, что в наибольшей степени сокращение объема (с параллельным возрастанием упругости и теплостойкости) было характерно для криогелей, проинкубированных в среде смешанного растворителя с соотношением ДМСО/Н₂О=66.4:33.6 (об. %), что отвечает составу, оптимальному для существования нековалентных Н-связанных комплексов, включающих 1 молекулу диметилсульфоксида и 2 молекулы воды.

PPy and PPy-based composites were prepared. The composites were synthesized by adding TiO₂ and Co₃O₄ metal oxides to PPy matrix. These three materials were tested for their ability to adsorb Congo Red (CR) dye. Their structure, morphology, and textural properties were analysed using XRD, FTIR, SEM–EDX and BET-BJH. The surface charge was measured using the point of zero charge (pH_pzc). The results showed that the metal oxides were successfully incorporated to the polymer, which changed the surface morphology, pore structure, and surface charge characteristics. The effects of contact time, initial dye concentration, pH and temperature on adsorption were studied. PPy has the largest BET surface area (195.47 m²/g) as compared to TiO₂/PPy (19.73 m²/g) and Co₃O₄/PPy (22.75 m²/g). TiO₂/PPy sustained the highest CR adsorption capacity (351.75 mg/g), and this is due to synergistic effects nascent from the combined PPy functional groups and TiO₂ surface chemistry. Co₃O₄/PPy exhibited the highest affinity for CR, attributable to the specific interaction between the Co²⁺/Co³⁺ sites and the anionic dye molecules. Kinetic results showed that the Shrinking Core Model (SCM) captured the experimental data best compared to pseudo-first order and pseudo-second kinetic models. The superior fit of the SCM suggests that a mixed mechanism controls diffusion through external film and intraparticle diffusion. Adsorption isotherm curve-fitting results showed that the Langmuir-Freundlich model provided the best fit for equilibrium data for CR adsorption, indicating both surface heterogeneity and non-uniform distribution of adsorption energies. Thermodynamic parameters revealed that the adsorption of CR is spontaneous and thermodynamically favourable.

Multilayer transport of non-Newtonian fluids through anisotropic porous media under magnetic fields is central to many engineering and biomedical applications, yet the combined influence of permeability anisotropy and magnetic control on layered flows remains insufficiently understood. The steady, incompressible, and laminar flow of a Casson–Jeffrey fluid system between two parallel plates filled with an anisotropic porous medium is analyzed in the presence of a uniform inclined magnetic field. The immiscible multilayer configuration consists of a Casson fluid core sandwiched between two Jeffrey fluid layers (J–C–J), enabling detailed examination of interfacial and anisotropic effects. A rigorous magnetohydrodynamic model incorporating directional permeability is developed, and the governing equations are nondimensionalized to introduce the anisotropic permeability ratio, anisotropy angle, Hartmann number, and Casson and Jeffrey fluid parameters. Exact analytical solutions for the velocity field are obtained. The results reveal that increasing permeability anisotropy and magnetic field strength suppress fluid velocity and interfacial shear, while the applied magnetic field provides an effective mechanism to regulate and stabilize multilayer flow in anisotropic porous channels. These findings offer physical insight into flow control in anisotropic porous systems, with applications in enhanced oil recovery, biomedical transport, composite material processing, and magnetically tunable microfluidic devices.

We propose a detailed study of the electroosmotic and pressure-driven flow of power-law fluids through soft nanochannels grafted with polyelectrolyte layers (PELs). The model incorporates the effects of finite ion size using the Carnahan−Starling-based ionic activity coefficient, ion separation caused by the Born energy difference at the PEL-electrolyte interface, and the dielectric permittivity contrast between the two media, all of which are incorporated in a modified Poisson−Boltzmann framework. A power-law model represents the fluid's non-Newtonian rheology, allowing for the consistent treatment of both shear-thinning and shear-thickening behaviours under typical nanochannel configurations. The fluid flow in and outside of the polymer brush layer is described using modified Darcy−Brinkmann and Cauchy momentum equations, accounting for both no-slip and interfacial slip conditions. Numerical solutions using finite difference approaches go beyond the limited Debye−Hückel linearization, allowing reliable predictions even at high surface charge densities. The results reveal that increasing ion size and flow behaviour index reduces average flow velocity, whereas high pressure gradients and fixed charge density increase it. Ion selectivity in shear-thinning fluids decreases with increasing pressure gradient due to hydrodynamic dominance over electrostatic interactions, while viscous drag maintains high selectivity. These findings offer new insight on coupled electrohydrodynamic transport in soft nanochannels and provided an improved foundation for designing next-generation nanofluidic devices for ion separation, purification, and biosensing applications.

Titanium dioxide nanoparticles (TiO₂ NPs) were synthesized via a controlled sol–gel method and subsequently functionalized with tannic acid (TA). The interaction of TA with TiO₂ nanoparticles was evidenced by a visible color change and FT-IR analysis, consistent with surface complexation between phenolic groups and Ti⁴⁺ sites. The adsorption of cationic dyes, rhodamine B (RB) and crystal violet (CV), onto TA-functionalized TiO₂ (TAT) was systematically investigated at room temperature by varying pH, initial dye concentration, contact time, and TAT dosage. Rapid dye uptake (>90% within 5 min) was observed for both dyes. Kinetic data were better described by the pseudo-second-order model than the pseudo-first-order model, reflecting adsorption controlled by surface site availability rather than a single diffusion step. Dye adsorption was largely pH-independent over the range of 3–9. Equilibrium data fitted the Langmuir model, suggesting monolayer adsorption with maximum capacities of 34.5 and 31.8 mg/g for RB and CV, respectively. TAT exhibited excellent reusability, retaining over 95% of its adsorption capacity after ten adsorption–desorption cycles using ethanol and inorganic acid. Overall, these results demonstrate that TAT is a stable, efficient, and regenerable bio-adsorbent for rapid removal of cationic dyes from water.