Colloid Journal最新文献

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.

Magnetorheological polishing technology is widely used in the processing of high-precision optical elements. One of the determining factors in the magnetorheological polishing technology is the nature and quality of a nanoabrasive present in a magnetorheological suspension. In this study, a method has been developed for the sol–gel synthesis of amorphous silica nanospheres used as a nanoabrasive for magnetorheological polishing of water-soluble crystals used to manufacture nonlinear optical elements for laser technology. The practical success has been achieved by incorporating the synthesized silica nanoabrasive into a magnetorheological suspension. The physicochemical characteristics of the resulting nanoabrasive have been presented. Electron microscopy data have confirmed the spherical morphology of SiO₂ particles, and it has been found that the particle size distribution varies in a range of 40–60 nm, thus ensuring the uniformity and high quality of treating the surfaces of optical elements with the magnetorheological suspension. The structure-related properties of the SiO₂ nanoabrasive have been studied by X-ray powder diffraction. The incorporation of the SiO₂ nanoabrasive into the magnetorheological suspension has made it possible to achieve the high-quality processing and cleanliness of the surface, as well as to ensure the finishing polishing of the surface of KDP single crystals to roughness values of no more than 6 Å. The results of the work are of interest for optimizing the process and improving the technology of magnetorheological polishing.

Gold, nickel and platinum nanoparticles (NPs) have been synthesized by impregnating single-crystalline silicon surface with precursors (aqueous solutions of corresponding salts). The morphologies of the formed nanostructured coatings have been studied, and the electronic structures of the synthesized NPs, as well as their adsorption properties with respect to H₂, O₂, and H₂O, have been determined. It has been found that oxidized nickel NPs are reduced by molecular hydrogen, while pure platinum NPs are oxidized by molecular oxygen already at room temperature. This phenomenon has not been observed for particles deposited in a similar way onto highly oriented pyrolytic graphite. In addition, it has been revealed that water molecules are formed on gold NPs as a result of the interaction between H₂ and O₂ in two stages, in contrast to the three-stage process (sequential exposure in H₂, O₂, and H₂), which is inherent in NPs deposited onto graphite. Differences in the adsorption properties of NPs of the same type deposited onto graphite and silicon are associated with the adsorption of a significant amount of the test gases on the latter.

Three samples of aqueous magnetic fluids based on magnetite particles stabilized with double layers of surfactants have been synthesized. The samples have been stabilized with lauric and oleic acids, as well as their salts, taken in three different combinations. The viscosity of the synthesized samples has been measured as depending on the concentration, temperature, and shear rate. With increasing temperature, the viscosity of a sample of the fluid stabilized with a double layer of lauric acid does not decrease relative to the viscosity of water, as has been previously observed for classical magnetic fluids, but rather increases. For a sample stabilized with two layers of lauric and oleic acids, the temperature dependence of the relative viscosity is nonmonotonic. The relative viscosity of a sample stabilized with a double layer of oleic acid is actually independent of temperature. To determine the concentrations of the samples, measurements of magnetization curves were carried out followed by their granulometric analysis. It has been found that the dispersity of the samples remains unchanged upon dilution. The initial magnetic susceptibility of the fluid samples has been shown to increase with concentration more slowly than it has been predicted by the modified effective field model. In contrast to the effective field model (and other ones), the coefficient at the quadratic term in the expansion of the initial susceptibility in terms of the Langevin susceptibility has turned out to be significantly lower than 1/3. Thus, new theories of dipole–dipole interparticle interaction must be developed to describe the properties of magnetic fluids stabilized with double layers of surfactants.

It has been shown that the Pd(Acac)₂–mod–H₂ colloidal system, where mod denotes chiral stabilizers of molecular (8S,9R)-cinhonidine, (–)-Сin, and ionic (–)-Cin*HCl and (–)-Cin*2HCl types, exhibits catalytic activity in the asymmetric hydrogenation of N-acetyl-α-amidocinnamic acid (AACA) at room temperature and an H₂ pressure of 5 atm. The esterification reaction of the product, N-acetylphenylalanine (N-APhA), occurs in the presence of protonated forms of cinchonidine. The excess of the R-(–)-enantiomer of N-acetylphenylalanine is as large as 78% for the Pd(Acac)₂–(–)-Сin–H₂ system at (–)-Сin/Pd = 1.5, while the protonated forms of the quinine alkaloid show lower efficiency as modifiers of the catalytic system with respect to chiral induction. The X-ray diffraction analysis and high-resolution transmission electron microscopy have been employed to show the formation of palladium nanoparticles with average sizes of 5.3 ± 0.8 and 4.2 ± 0.5 nm for the Pd(Acac)₂–(–)-Cin–H₂ and Pd(Acac)₂–(–)-Сin *HCl–H₂ systems, respectively.