Colloid Journal最新文献

In the last two decades, a great interest has been focused on the creation and study of superhydrophobic nanomaterials based on the “lotus effect.” This effect is caused by the heterogeneous wetting of rough surfaces, when the grooves of a rough surface are filled with air (vapor) and water contacts only with the tops of the protrusions. A drop forms a sphere on the surface and rolls down picking up dirt particles when the surface is slightly tilted. Diverse methods have been developed for producing such materials, and the potential of the ion-track technology (ITT) is being investigated. The goal of this work is to study the wettability of surface microtextures by the examples of two materials with different initial degrees of hydrophobicity. The ITT has been employed to obtain samples with maximum water contact angles of 140 ± 5° and 151 ± 5° by modifying the surfaces of polycarbonate and polypropylene films, respectively. It has been shown that such angles are characteristic of microtextures, for which surface fraction f that is in contact with a droplet is decreased to a range of 0 < f < 0.3. Materials with tilted microtextures have been obtained in order to increase the probability of droplet rolling down a material surface in a certain direction. In this case, the wettability becomes anisotropic. A droplet loses its spherical shape and is deformed in the direction of the tilt of needle-like surface elements. It has been found that the anisotropy of wettability is higher at a tilt angle of the texture elements of 45° than that at 30° (relative to the flat surface).

A method has been developed for the formation of hybrid membranes consisting of a hydrophilic microporous substrate and a hydrophobic nanofibrous polymer layer deposited by electrospinning. A track-etched poly(ethylene terephthalate) membrane has been used as the hydrophilic microporous substrate, onto the surface of which a thin layer of titanium is deposited by magnetron sputtering to provide the nanofibrous layer with adhesion. Simultaneously, this layer has been used as an electrode of a deposition collector for the electrospinning formation the nanofibrous coating. It has been shown that the application of this method for the preparation of polymer coatings using poly(vinylidene fluoride) as a starting material for the formation of nanofibers makes it possible to obtain a highly hydrophobic layer, the surface of which has an average water contact angle of 143.3 ± 1.3° depending on the deposition density. The morphological study of the nanofibrous coating has shown that its microstructure is typical of nonwoven materials. The nanofibers that form the porous system of this layer have a wide scatter of sizes. FTIR spectroscopic and X-ray diffraction investigations of the molecular structure of the nanofibrous layer have shown that the β-phase prevails in its structure, with this phase being characterized by the maximum dipole moment. It has been shown that the elaborated hybrid membranes ensure high separation selectivity of desalinating an aqueous 26.5 g/L sodium chloride solution by the membrane distillation method. In the studied regime of the membrane distillation, the salt rejection coefficient for membranes with nanofibrous layer densities of 20.7 ± 0.2–27.6 ± 0.2 g/m² is 99.97−99.98%. It has been found that the use of a highly hydrophobic nanofibrous layer with a developed porous structure in combination with a hydrophilic microporous substrate 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 value depends on the density of the deposited nanofibrous layer.

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 low-density 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.

The green synthesis of gold nanoparticles (AuNPs-E) by bioreduction of chloroauric acid (HAuCl₄), using the aqueous extracts (E) of blackberry (Rubus spp.) leaves, was presented in this work. The E were obtained by maceration at room T and reflux extraction at boiling T, while the AuNPs-E were synthesized at room T and T = 80°C. The synthesized AuNPs-E were structurally and physicochemically characterized by UV-Vis and FTIR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS) and zeta potential measuring. The changes in the FTIR spectra suggested that biocompounds containing C=O, C–O–C, and OH functional groups play the main role as capping and stabilizing agents providing the stability of AuNPs-E confirmed by UV-Vis spectroscopy. The crystal structure was proved by XRD analysis confirming the (111) reflection plane at 2θ = 38.2° as dominant in the AuNPs-E face-centered cubic lattice. Negative zeta potential of AuNPs-E in the range of –11.67 ± 0.45 and –17.70 ± 0.27 mV suggests moderate stability of AuNPs-E with the average size in the range of 61.6 ± 11.5 to 93.9 ± 1.4 nm determined by DLS. The qualitative and quantitative presence of Au in the formed AuNPs-E, together with the elements from the extracts’ biomolecules, was proven by the EDX spectroscopy. Finally, the antioxidant and antibacterial activities of AuNPs-E were tested by DPPH test and disc diffusion method, respectively, suggesting that AuNPs-E synthesized by described method should be certainly taken into consideration, alone or in combination with the silver nanoparticles, in dermal and cosmetic preparations design.

Ceramide 2 is the main lipid of stratum corneum and a popular component in skin healthcare products. But developing ceramide 2 based corneal protecting product is troublesome due to its insoluble feature in water. In this work, a novel type of inclusion nanoparticle was developed to solubilize and enhance the corneal repair effect of ceramide 2 by the anti-solvent method. It was revealed that the types of solvents and cyclodextrins influenced the precipitation rate as well as the stability of intermediate clusters of ceramide 2, where DMSO with moderate supersaturation promoted the formation of inclusion complex with β-cyclodextrins. The ceramide-cyclodextrin inclusion complex had an amphiphilic structure, which could self-assemble into nanoparticles in water, as evidenced by disappeared endothermic peaks of ceramide (78°C) and cyclodextrin (120°C), as well as appearance of two endothermic peaks corresponding to nanoparticle transition (45°C) and dissociation of cyclodextrin inclusion complex (102°C). Upon treating rat damaged skins with ceramide 2 inclusion nanoparticles, the cumulative permeation of indomethacin (IND, a model drug for skin permeability) were found to be 330.80 ± 54.86 μg/cm², which was significantly lower than the control group (472.47 ± 154.83 μg/cm²). In comparison, water suspensions of ceramide 2 showed no corneal repair effect.

In the present work, the volumetric and conductometric studies to find the interactions between amino acids DL-Valine and DL-Serine with cationic and anionic surfactants, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) in aqueous solutions at different temperatures and atmospheric pressure were carried out. The effect of pre- and post-micellar concentrations of surfactants on the physicochemical properties was also studied. The densities measured experimentally were used to calculate the thermodynamic parameters such as the apparent molar volumes, ϕ_v, partial molar volumes, (phi _{{text{v}}}^{{text{0}}}), transfer volumes, (phi _{{text{v}}}^{{text{0}}}) (tr), and partial molar expansibilities, (phi _{{text{E}}}^{0}) at temperatures from 288.15 to 303.15 K while the conductivity data obtained at different temperatures from 293.15 to 318.15 K were used to obtain the molar conductivities (({{{{Lambda }}}^{0}})) as well as limiting molar conductivities ((Lambda _{{text{m}}}^{0})) from specific conductivities (κ) which reflect the interaction prevailing within the studied systems. In addition, the UV-visible absorption spectroscopy at 298.15 K has also been performed in the presence of fluorescein to study the interaction within above mentioned systems.

In the present work, the impact of periodic body acceleration on the unsteady flow of blood in an inclined artery has been investigated. The blood is represented by an incompressible, viscous, non-Newtonian Jeffrey fluid. The artery is assumed to have mild overlapping stenoses inside its lumen. The perturbation method is used to solve the governing nonlinear coupled partial differential equations. Here, the Womersley frequency parameter is considered small enough for blood flow through arteries. Analytic expressions for the wall shear stress, stress at the critical height of stenosis, velocity profile, volumetric flow rate, pressure drop, resistive impedance, and effective viscosity are obtained using the perturbation technique. Regarding different flow parameters, the effects of body acceleration, pulsatility, the non-Newtonian character of blood, and velocity slip are examined and graphically depicted. It is concluded from the present analysis that the flow impedance rises when the stenosis reaches its critical height, but it falls as the velocity slip at the wall increases. It is also observed that when body acceleration increases, flow rate, velocity, and shear stress near the critical height of stenosis ({{tau }_{c}}) all rise, whereas wall shear stress ({{tau }_{w}}) decreases as body acceleration rises. Here, we also analyzed the flow pattern of the non-Newtonian Jeffrey fluid when it passes through the overlapped stenosed artery with the help of streamlines. The results of the present problem have been verified with the previous existing results in the literature.

The work is devoted to studying changes in the physicochemical and colloid–sorption properties of bleaching clay thermotreated after its use in the process of refining vegetable oil. Bleaching clay thermotreated at different temperatures has been used for comparison. The colloid–sorption properties have been studied by measuring adsorption of methylene blue dye from aqueous solutions. It has been shown that clay annealed at 350°C adsorbs methylene blue most efficiently. In the saturation region, the adsorption by clay thermotreated at 350°C has amounted to 0.28 mmol/g or 89.6 mg/g, while the adsorption by clay annealed at 250°C has appeared to be 0.24 mmol/g or 76.8 mg/g. When the annealing temperature is elevated above 500°C, the adsorption properties of the bleaching clay waste decrease, probably, due to the combustion of the carbon layer. Using bleaching clay waste from the Alekseevsky oil extraction plant as an example, it has been revealed that, during the thermal treatment of the material, various types of water (free, interpackage, and chemically bound one) are removed, thus leading to changes in the colloid–sorption properties, such as particle surface relief, specific surface area, sorption capacity, and ζ potential.

Dynamic light scattering has been employed to investigate aqueous Pluronic P123 solutions at different temperatures and in the presence of different solvents and quercetin additives. Significant changes have been revealed in the average particle size and polydispersity index depending on the conditions. The effect of temperature on micellization of the block copolymer in aqueous solutions has been studied in a range T = 15–45°C, which is most often considered when using P123 in the sol–gel synthesis of silica. The most pronounced effect of temperature on the micellization of the studied surfactant has been observed at T = 15–20°C. In this temperature range, the scattered light intensity distribution over particle sizes has a polymodal character, which indicates the presence of macromolecules, micelles, and their aggregates in the system. A further increase in temperature up to 45°C causes no significant changes in the particle size. In aqueous solutions, micelles with a narrow size distribution (minimum polydispersity index) are formed within temperature ranges of 21–25 and 35–40°C. Substantial effects have been found when adding alkanols and polyphenolic substances as solubilizers capable of influencing the structure of micelles both in their bulk and on the surface of polar moieties of the surfactant. It has been shown that, in the presence of butanol-1, micelles are stabilized at temperatures of 15–20°C. At T > 30°C, the structure of micelles is transformed. As the fraction of butanol-1 in the solution increases, its influence is manifested at lower temperatures. It has been noted that ethanol has a destructive effect on micelles. Additives of quercetin exhibit an opposite effect of micelle stabilization, which leads to the formation of a homogeneous surfactant structure. It has been shown that, by varying solvent composition, the flavonoid–micelle binding can be controlled due to changes in the solvation. The greatest influence of quercetin on the structure formation of P123 has been observed at a solvent composition corresponding to ethanol-to-block copolymer molar ratio of n(EtOH) : n(P123) = 80 : 1.

The present article deals with the modulation of electroosmotic flow (EOF) and transport of ionic species within soft nanochannels. The power-law model is adopted to consider the non-Newtonian nature of bulk electrolyte. The soft layer grafted along the rigid walls often bears ionizable functional groups, which in turn leads to the net volumetric charge. Besides, the dielectric permittivity of the soft layer is in general lower than that of the ambient electrolyte solution, which in turn leads to ion partitioning effect. The net volumetric charge within the soft polymeric layer coated along the channel walls may be moderate to large. For such a case, the ion steric effect may play a pivotal role on the modulation of electrostatic potential and thereby the flow field across the channel. In the present article, we aim to study the flow modulation across the soft nanochannels considering all such intrinsic effects. The mathematical model is based on modified Poisson−Boltzmann equations based on Carnahan−Striling model, Cauchy momentum equation for flow field. The governing equations are solved via a suitable numerical scheme based on finite difference method to calculate the electrostatic potential as well as flow velocity. We further analyze the impact of pertinent parameters on the flow modulation and ion selectivity parameter.