The kinetics of generation of the circular dichroism signals characteristic of the cholesteric liquid-crystalline dispersions of DNA are compared with the results of their detailed study using confocal microscopy. Three processes of the dispersed particle evolution have been experimentally confirmed (characteristic time intervals are given in the parentheses): (1) growth due to the attachment of DNA molecules (tens of seconds); (2) coalescence accompanied by the rearrangement of cholesteric layers (minutes); and, finally, (3) aggregation resulting in the formation of large clusters of irregular shape that has a threshold dependence on the concentration of the nucleic acid (hours). It has been suggested that the latter have no “integral” optical activity.
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 provide an improved foundation for designing next-generation nanofluidic devices for ion separation, purification, and biosensing applications.
The recovery of phenol from aqueous solutions using CeO2−SiO2 nanocomposites was investigated. The optimal pH value for the process was determined to be 3. Higher phenol concentration decreased separation efficiency while increasing adsorption capacity. Conversely, increasing the adsorbent dosage led to a higher separation efficiency but lower adsorption capacity. The highest batch adsorption capacity (136 mg/g) and maximum efficiency were achieved with CeSi-3 (CeO2 : SiO2 = 1 : 0.5), which possesses the highest cerium oxide content. Higher temperatures reduced both adsorption efficiency and capacity. Thermodynamic parameters indicate that the process is non-spontaneous and exothermic. The isotherm, thermodynamic, and kinetic analyses demonstrated that the adsorption process was governed by a combination of physical and chemical interactions. Complete desorption (100
Polypyrrole (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 (pHpzc). 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 showed the highest CR adsorption capacity (351.75 mg/g), and this is due to synergistic effects arising 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.
Direct numerical simulation of the electrophoresis of a charged dielectric microparticle is performed using a coupled nonlinear system of Nernst–Planck–Poisson–Stokes equations within a range from weak to strong electric fields. The goal of the study is to compare the electrophoretic mobilities and the structures of the ion transport in polar and nonpolar electrolytes at a fixed particle surface charge. Two characteristic values of the Debye length, which correspond to thin and relatively thick electrical double layers, are considered to describe these two types of media. The particle surface charge is fixed at a value corresponding to the regime, in which pronounced nonequilibrium effects and the ionic cloud deformation are expected at a sufficiently high electric field strength. The main attention is focused on the dependence of the dimensionless mobility on the electric field strength and control parameter κ, which determines the intensity of the electrokinetic interaction and the influence of hydrodynamics on the ion transport. It has been shown that an increase in the field strength makes the response essentially nonlinear and is accompanied by an enhancement of the concentration polarization and changes in the spatial distributions of ion concentrations and space charges. Parametric dependences of the electrophoretic mobility have been compared for the two characteristic Debye lengths, and parameter ranges have been determined in which the difference between the polar and nonpolar media is mainly quantitative, as well as the ranges corresponding to qualitative changes in the transport regime. For the characteristic regimes, spatial distributions of the total ion concentration and charge density are presented, thus making it possible to relate the changes in the mobility with the changes in the structure of ion fluxes and the volumetric electric force. The obtained results provide criteria for the onset of a nonequilibrium regime and can be used for interpreting experiments and designing electrokinetic microsystems in polar and nonpolar electrolytes.
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 NPs 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
Noncovalent poly(vinyl alcohol) (PVA) cryogels (PVACGs) have been formed by freezing of 100 g/L PVA solutions in water or dimethyl sulfoxide (DMSO) at –20°C for 12 h followed by defrosting of the samples at a rate of 0.03°C/min. These cryogels have then been incubated in H2O/DMSO mixtures with different volume ratios. Dielectric spectrometry has been used to determine the dielectric permittivity of these mixed solvents to characterize their polarity. Changes (relative to the initial cryogels) in the volume, elasticity modulus, and thermophysical fusion parameters have been evaluated for PVACG samples treated with these mixtures. It has been shown that the greatest degree of shrinkage (with a parallel increase in the elasticity and heat endurance) is inherent in cryogels incubated in a mixed solvent medium with ratio DMSO/H2O = 66.4 : 33.6 (vol
Isothermal molecular dynamics, the LAMMPS program, and embedded atom method, have been employed to simulate the uniform heating of ternary Pt1700Pd1700Cu5100 nanoparticles (consisting of 8500 atoms, about 6.4 nm in size) and subsequent cooling (quenching) of nanodroplets to a final temperature of 300 K. The results obtained for the nanoparticles of this size have been compared with the data on smaller particles (4.6 nm) with the same percentage of the components (Pt20
Silver organosol films have been produced by the dip-coating method. The organosol has been stabilized with sodium bis(2-ethylhexyl) sulfosuccinate. The films consist of silver nanoparticles ( 20 nm) encapsulated in an organic stabilizer layer ( 1 μm). Temperature-induced changes in the surface properties of the films have been investigated. Heat treatment in a range from 25 to 500°C causes significant effects. The film surface becomes more hydrophilic. Surface roughness significantly changes from 16 to 172 nm. The observed changes result from stabilizer decomposition and sintering of silver nanoparticles. Meanwhile, the treatment leads to substantial changes in the plasmonic properties of the films. The surface plasmon resonance (SPR) signal intensity decreases by 53
The present investigation employs a conductometric approach to investigate the influence of differing concentrations of the antibiotic drug sulfathiazole (STZ) and the additives glucose/urea on the micellization behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in a slightly acidic environment (pH 5.0) across a range of temperatures. The aim of this study is to elucidate the influence of surfactant-drug interactions on micelle formation and dynamics, thereby establishing the possibility of advancing drug delivery systems and enhancing the therapeutic efficacy of drugs. Unlike CTAB in pure water, the CMC (critical micellar concentration) values of CTAB decreased in the presence of STZ, i.e., micellization was facilitated. Both glucose and urea increase the CMC of the CTAB + STZ system. Unlike urea, which destabilizes water structure and diminishes hydrophobic contacts, glucose stabilizes the water structure, making it harder for CTAB molecules’ hydrophobic tails to form micelles. The relationship between the CMC of the CTAB + STZ and temperature displayed a linear trend for both aqueous media and aqueous glucose/urea environment. Thermodynamic parameters (change in entropy of micellization, Δ S_m^0 ; enthalpy of micellization, Δ H_m^0 ; and Gibbs free energy of micellization, Δ G_m^0 ) and physicochemical variables (CMC and counterion dissociation, α) have been used to characterize the interaction between CTAB and STZ. The negative Δ G_m^0 values reveal that the CTAB + STZ mixture undergoes spontaneous micellization in both pure water and aqueous glucose/urea environments. The values of − Δ H_m^0 and + Δ S_m^0 for the CTAB + STZ mixture indicate that both electrostatic and hydrophobic interactions play a crucial role in aggregation.
A biogenic strategy was employed to develop a multifunctional magnetic nanocomposite by first synthesizing cobalt ferrite (CoFe2O4) nanoparticles (NPs) and subsequently functionalizing them with lemon peel extract (LPE) rich in phenolics and flavonoids. The LPE acted as a biogenic reducing and stabilizing agent, facilitating the in situ decoration of silver nanoparticles (Ag NPs) and yielding a novel ternary nanocomposite (Ag/LPE–CoFe2O4). Successful functionalization and Ag incorporation were confirmed by FTIR, XRD, FESEM, XPS, HRTEM, EDX and VSM. The Ag/LPE–CoFe2O4 nanocomposite exhibited noticeably enhanced antimicrobial activity against Gram-positive (S. aureus, B. subtilis), Gram-negative (K. pneumoniae, E. coli), and fungal strains (Candida, Aspergillus), resulting from the synergistic action of CoFe2O4, LPE phytochemicals, and Ag NPs. Catalytic tests further exhibited rapid reduction of 4-nitrophenol to 4-aminophenol under ambient conditions with a rate constant of 0.28 ± 0.02 min−1 and complete conversion is achieved in 14 min. This study highlights the novelty of promoting citrus peel waste to engineer an Ag-decorated, magnetically retrievable nanocomposite that integrates recyclability, catalytic efficiency, and broad-spectrum antimicrobial activity. These results demonstrate Ag/LPE–CoFe2O4 NPs as an eco-friendly multifunctional nanocomposite with strong potential in environmental remediation and biomedical fields.
The study investigates the effect of the acidity of a hydrogen tetrachloroaurate solution (1−9 М HCl) on the optical properties, hydrodynamic diameter, and electrokinetic potential of gold nanoparticles. In addition, the effect of the molar fraction of oleic acid (up to 80
The effect of F−, Cl−, Br−, and I− halide ions on the behavior of lysozyme in an aqueous−toluene system and the bacteriolytic activity of the enzyme has been studied. The addition of NaF causes lysozyme molecules to form a denser layer at the interfaces due to the stabilization of protein globules and the enhancement of hydrophobic interactions. As a result, the addition of NaF does not affect the enzymatic activity of lysozyme. A different effect has been found upon the addition of NaCl at the same molar concentration. It decreases both adsorption and catalytic activity of the enzyme. The probable reason is the efficient screening of electrostatic interactions, as well as the mutual compensation of hydrophobic attraction and steric repulsion. Chaotropic anions enhance the intermolecular attraction in the adsorption layer, but, at the same time, reduce the catalytic activity. In the case of a strong chaotrope (NaI), this is explained by the destabilization of the network of hydrogen bonds both in the solvent and in the structure of the protein itself, thus increasing the affinity of the protein for the hydrophobic surface; however, it negatively affects its enzymatic function. The key factor determining the catalytic parameters (vmax and Km) in the presence of cosmotropic anions and a weak chaotrope (NaBr) is the molar concentration of a salt: as it increases, the parameter values decrease. At the same time, the vmax/Km ratio for these anions remains almost independent of the concentration, while bromide anions appear to be most favorable for maintaining lysozyme activity among the studied salts.
The paper reports the synthesis of a sulfur-containing amphiphilic derivative, BODIPY B2S, as well as the methods for its purification, and the characteristics of this compound (NMR, IR spectroscopy, mass spectrometry), which can be used as a chelator for mercury(II) cations. The effect of the film structural organization on the efficiency of supramolecular recognition of Hg2+ ions has been determined on the basis of the analysis of the structure, properties, and phase behaviour of B2S in ultrathin films on liquid and solid substrates. The structural changes accompanying molecular transitions in planar systems have been studied using Langmuir monolayer compression isotherms, in situ reflection-absorption UV−Vis spectroscopy, optical absorption spectroscopy, and fluorescence spectroscopy. It has been shown that the disruption of dye associates upon complexation leads to the enhancement of monomer emission and alters the fluorescence colour of Langmuir–Blodgett films formed at a high surface pressure. This phenomenon can serve as a convenient diagnostic indicator of mercury cation binding.
This work examines the specific response of aqueous sulfonated polyphenylquinoxaline gels to temperature field exposure. This response manifests itself as an exothermic effect, the position of which in the temperature scale depends on the gel thermal prehistory. The observed exothermic effect is not associated with a phase transition; its manifestation requires the presence of a spatial network structure containing both free and bound solvent. This phenomenon is likely to be caused by relaxation-type exchange processes between the free solvent and the gel network. The influence of the free solvent redistribution in the network of the gel on its thermophysical and viscoelastic properties has been determined.
Macroporous cryogels with and without the additives of chaotropic and kosmotropic substances (urea, guanidine hydrochloride, trehalose, and hydroxyproline) were prepared by freezing a 100 g/L aqueous solution of poly(vinyl alcohol) (PVA) at—20°C, maintaining it at this temperature for 12 h, and then thawing it while heating at a rate of 0.03°C/min. Also, these chaotropic and kosmotropic substances were introduced into the PVA cryogel matrix without additives by saturating the gel materials in the respective aqueous solutions. These same substances were added by saturating the gel materials in the corresponding aqueous solutions. The character of changes in the physicochemical parameters of PVA cryogels formed in the presence of lyotropic agents and PVA cryogels after saturation of the gel samples in the water solutions of these substances was studied. It was shown that chaotropic substances negatively affect the elasticity and heat endurance of the resulting materials, while the presence of kosmotropic additives in the cryogel matrix leads to its strengthening and increased thermal stability. Moreover, this effect is observed for both options of introducing low-molecular-weight substances into the cryogel matrix—when adding additives to the initial polymer solution before cryogenic processing and when incorporation of the same additives to the samples via saturation. However, for chaotropic substances, the saturation method allows for a significant increase in the working concentration of these substances while maintaining the elastic properties of the materials. Taking into account that PVACGs are used as carriers of low-molecular-weight water-soluble substances in various applied fields (medicine, biotechnology, art restoration, etc.), the obtained research results are of not only scientific but also of practical interest.
New-generation antibacterial surfaces must not only inhibit microbial growth, but also maintain their functionality when used as “touch surfaces” and self-clean under the influence of light. This paper proposes a simple approach to the formation of Cu–TiO2 composite coatings on copper foil, with the approach combining laser micro/nanotexturing and subsequent deposition of TiO2 nanodispersions of controlled polymorphic forms (anatase/rutile). It is shown that the coating retains its initial hierarchical roughness and a significant titania content after sonication in water. Photocatalytically induced self-cleaning of the coating under irradiation with wavelengths corresponding to the blue region of the visible light spectrum is more pronounced for anatase-containing composites. Moreover, the photocatalytic activity of the anatase-containing composite shifts toward the visible region relative to the initial anatase particles. This widening of the photoactivity region of the composites is due to the fact that copper oxide functions as a sensitizer, which absorbs visible light, thus leading to injecting electrons from copper oxide to the conduction band of anatase in the presence of a heterojunction. Irradiation has different effects on composites with different polymorphic modifications when they are exposed to saline: e.g., anatase enhances the accumulation of dissolved copper, while rutile reduces its concentration relative to unirradiated conditions. Thus, in the method proposed for preparing the composites, polymorphic forms of TiO2 enable one to control the self-cleaning and the ionic response of copper, i.e., the key parameters of photoactive coatings intended for antibacterial applications.
Cation-conducting hybrid membranes based on poly(vinyl alcohol) modified with furfural, aminosulfonic acid, and tetraethoxysilane have been obtained by the liquid-phase synthesis method in dimethyl sulfoxide. Some of the membranes contain cerium dioxide nanoparticles previously obtained in benzyl alcohol and dispersed in dimethyl sulfoxide using ultrasonic and mechanical homogenizers. The conditions have been determined for obtaining a monodisperse (polydispersity index is 0.08) colloidal CeO2 solution with a particle size of 84 nm. The composition, surface morphology, and physicochemical properties of the obtained materials have been studied. It has been found that the specific ionic conductivity of the hybrid membrane material decreases from 8.4 × 10–2 to 3.1 × 10–2 S/cm upon the addition of cerium dioxide, while its oxidative (chemical) stability determined using Fenton’s reagent simulating aggressive operating conditions of a fuel cell increases by 1.5 times. Moreover, in the presence of the metal oxide, the thermal stability and moisture-retaining capacity increase, whereas the degree of membrane swelling in water decreases. The operating temperature range of the obtained cation-conducting hybrid materials with and without cerium dioxide is much wider than that of the Nafion reference membrane.
In this paper, SiO2 xerogel has been synthesized by neutralizing sodium silicate with hydrogen sulfide and its adsorption properties for copper(II) ion removal have been studied with allowance for its morphological and structural characteristics. The synthesized adsorbent has been characterized using electron microscopy, high-resolution transmission microscopy, infrared spectroscopy, and energy-dispersive analysis. The specific surface area of the synthesized SiO2 xerogel has been 145 m2/g, while the monolayer volume has been 34 cm2/g. The dependence of the adsorption characteristics of the synthesized SiO2 xerogel on pH has been studied and the mechanism of ion exchange and saturation time have been identified. Maximal adsorption efficiency has achieved at pH 4–5, with the process occurring rapidly within the first 20 min. The adsorption isotherms have corresponded to the Langmuir model. The thermodynamic and kinetic aspects of copper(II) ion adsorption on the synthesized SiO2 xerogel have been studied. Kinetic analysis has shown that the pseudo-second-order model has better described the adsorption of copper(II) ions on SiO2 xerogel. The mechanism of copper(II) ion adsorption on SiO2 xerogel has been considered.
