Colloid Journal最新文献

A modification of the “Stefan’s rule” for the surface tension coefficients of liquids has been proposed, with the modification consisting in choosing a liquid as a system of comparison with respect to its surface. An expression for the surface tension coefficients has been derived and employed to interpret their temperature dependences for a number of molecular liquids with different physicochemical properties.

“Primary” poly(vinyl alcohol) (PVA) cryogels have been obtained by cryogenic processing (freezing at –21.6°C for 12 h followed by defrosting via heating to 20°C at a rate of 0.03°C/min) of a 100 g/L solution of PVA in dimethyl sulfoxide (DMSO) in the absence and presence of urea (2 or 4 mol/L), which exhibits kosmotropic properties in such a medium. Subsequent hydration of the cryogels by replacing DMSO with water causes a decrease in the volume and weight of the samples, as well as leads to a significant increase in the elasticity modulus of resulting “secondary” cryogels. The absolute magnitude of such effects depends both on the concentration of urea in an initial PVA solution and on the volume ratio between gel samples and an aqueous extractant during their hydration. Using optical microscopy, it has been found that the presence of urea in the initial DMSO polymer solution in a concentration close to the limit of its solubility in such a medium induces the formation of a gel matrix with a wide-pore morphology. Since high-modulus secondary PVA cryogels are of great interest as materials for biomedical applications, the possibility of their functioning as carriers of drug delivery systems has been assessed in the work. Ibuprofen sodium salt has been used as a model drug. The analysis of the release kinetics of this substance within the framework of the Weibull function has been employed to show that the dynamic hydrogen bonding of its carboxylate groups with the hydroxyl groups of PVA decelerates the release of the drug from the polymer carrier, i.e., prolongs the release process. At the same time, the rate of the process depends on the urea content in the initial polymer solution most likely due to microstructural differences between the polymer phases of the macropore walls in the cryogel matrix.

Nanodispersions can be used to solve various practical problems, such as increasing the efficiency of heating systems, cooling of electrical equipment, intensifying oil recovery, etc., because dispersing nanoparticles in liquid media provides an inexpensive and convenient way to significantly improve various functional properties of a base fluid. Although the influence of dispersed particles on surface phenomena in systems comprising nanofluids has been studied for more than 30 years, due to a number of factors, the problem of appropriate and self-consistent description of the behavior of nanofluids will apparently remain to be the focus of scientific attention in the coming decades. This paper presents a brief review of recently published results that are of general importance for understanding the behavior of the surface tension of nanofluids, as well as the processes accompanying wetting with nanofluids and their spreading over various surfaces.

Macroporous cryogels of poly(vinyl alcohol) (PVA) have been prepared by the cryogenic processing (freezing at –20°C for 12 h followed by defrosting through heating at a rate of 0.03°C/min) of aqueous PVA solutions with a polymer concentration of 100 g/L. The character of changes in the physicochemical parameters of the cryogels has been studied after equilibrating their samples with aqueous solutions of amino acids of general formula H₂N–(CH₂)_n–COOH (n = 1–5). It has been shown that these amino acids, glycine (n = 1) and ε-aminocaproic acid (n = 5) to the highest and lowest extent, respectively, impose a kosmotropic action on the properties of the PVA cryogels causing a decrease in their volume, a significant increase in the compression elasticity modulus, and a rise in the fusion temperature of the samples. Nevertheless, H₂N–(CH₂)_n–COOH amino acids are released from the cryogels saturated with amino acid solutions into an external aqueous environment with no significant diffusion hindrances. After cryogels loaded with amino acids are exhaustively rinsed with pure water, their physicochemical parameters do not return completely to the values observed for the samples before their treatment with solutions of such amino acids due to the formation of additional H-bonded nodes of a three-dimensional network, with their formation being promoted by kosmotropic amino acids in the bulk of the already formed cryogels.

Ethoxyamine derivatives of humic acids have been obtained by mechanochemical synthesis via the simultaneous interaction of humic acids with poly(ethylene glycol) (PEG-6000 and PEG-1500) and an aminating reagent (urea, hydroperitum, or cyanoguanidine) in a vibrating apparatus. Reaction products have been characterized by IR spectroscopy, acid–base potentiometric titration, and viscometry. Tensiometric and rheological characteristics of the surface layers of solutions of salts of the synthesized derivatives of humic acids have been studied by the pendant drop and oscillating pendant drop methods. The solutions of the salts of ethoxyaminohumic acids have been found to exhibit a pronounced surface activity at the air–water interface. The experimental dependences of the viscoelastic modulus on the surface pressure and the concentration of the solutions of ethoxyaminohumic acid salts are in satisfactory agreement with the functions calculated in terms of the theoretical model of bimolecular adsorption. The presence of amino groups in the structure of ethoxyaminohumic acids predetermines their high solubility in the acidic pH region. The simultaneous incorporation of ethoxy and amino groups into humic acid macromolecules makes it possible to obtain a novel type of surfactants, which combine three functions, i.e., the functions of anionic, cationic, and nonionic surfactants.

The goal of this study is to increase the energy efficiency of pipeline hydraulic transport of water-swellable aluminosilicate dispersions. A model commercial suspension, the filler of which is a complex mixture of aluminosilicates, has been used to develop an approach that makes it possible to improve the technological properties of such suspensions. Modification of the suspensions consists in adding organic and inorganic inhibitors of swelling of dispersed phase particles, as well as nonionic surfactants. The influence of the additives leads to a decrease in the yield stress and an increase in sedimentation stability of the heterogeneous systems. It has been shown that the use of the complex modifying additive prevents the particles of the model suspension from agglomeration and provides it with sedimentation stability at temperatures up to 70°C, which is important for the technical process in which the suspension is intended to be used. Technically, the research is of an applied nature. A well-known approach to modifying suspensions is used, which consists in combating the aggregation of dispersed phase particles and blocking ion exchange between them and the dispersion medium. The performed set of rheological shear and oscillation tests and the study of the sedimentation stability of the suspensions in the presence of various modifying additives have resulted in optimizing their composition. The practical result of the work is the successful hydrotransport of the suspension in which the content of the dispersed phase is 50% higher than that in the unmodified suspension, thus increasing the energy efficiency of the process.

The paper describes examples of microemulsions based on a well-known biocompatible surfactant, lecithin, and the possibilities of their use as drug carriers. The main problem encountered when developing lecithin microemulsions is the search for suitable cosurfactants. Molecules with short alkyl chains (4–5 C atoms) and relatively large polar “head,” such as short-chain aliphatic alcohols, acids, and amines are most suitable as cosurfactants for the preparation of lecithin microemulsions. Therewith, high concentrations of the cosurfactants (the cosurfactant : lecithin weight ratio usually is 1 : 1) are necessary. Most often, ethanol, n-propanol, or n-butanol are used as cosurfactants for the preparation of lecithin microemulsions in various natural and synthetic oils. To replace toxic alcohols with less toxic components, other well-known surfactants may be added to lecithin microemulsions. They are, e.g., Brij 96V (poly(ethylene glycol) oleate), Tween 80 (polyoxyethylene-20-sorbitan monooleate), Tween 20 (polyoxyethylene-20-sorbitan monolaurate). Triton X-100 (tert-octylphenyl ether of poly(ethylene glycol)) or oleic acid. Composites based on lecithin microemulsions have been described as means for local anesthesia and delivery of vitamins, as well as agents with anti-inflammatory, antifungal, anticancer, and wound healing effects. The considered examples show the promise of the study and development of lecithin microemulsions as drug carriers.

The review is focused on the etoposide delivery systems based on colloidal carriers, i.e., nanoparticles and micelles made of synthetic and natural polymers. Etoposide, a topoisomerase II inhibitor, occupies an important place in the chemotherapy of a number of tumors; however, its use is often limited due to severe side effects. The application of colloidal delivery systems makes it possible to change the pharmacokinetic parameters of etoposide and increase its accumulation in tumors leading to an increase in the antitumor effect. Of particular interest are stimuli-sensitive systems that respond to specific conditions in the tumor microenvironment, which can significantly increase the selectivity of the drug.

Pulmonary surfactant, which is a complex mixture of lipids and proteins, plays a key role in the functional properties of the respiratory system. Lipids form complexes with proteins to maintain low values of surface tension at continuous compression/expansion deformations. However, interactions that lead to the complexation still remain to be unknown thus significantly hampering the development of synthetic analogs of the natural pulmonary surfactant. In this work, the methods of surface rheology and ellipsometry have been employed to study the dynamic properties of model phospholipid monolayers applied onto the surfaces of synthetic polyelectrolyte solutions. It has been shown, that electrostatic or hydrophobic interactions between lipids and macromolecules are insufficient for the efficient complexation and maintenance of low surface tension values.

Nanoemulsions (NEs) and solid lipid nanoparticles (SLNs) are promising drug delivery systems. In this work, paraffin oil NEs and stearic acid SLNs stabilized with Tween 60 and Span 60 have been studied. NEs with an average droplet diameter of ~50 nm and suspensions of SLNs with an average size of ~30 nm are stable to aggregation for more than 90 days. The rates of penetration of lipid particles into cancer cells (C6 and MCF-7) depend on their sizes. After incubation for 1 h, lipid nanoparticles ~50 nm in size penetrate into cells, are distributed in their internal space, and concentrate in the nuclei. The cytotoxicity of doxorubicin- or thymoquinone-loaded NEs and SLNs against MCF-7 and HTC 116 cell lines is higher than the cytotoxicity of the individual substances. Wherein, unloaded NEs and SLNs show low cytotoxicity. The obtained results demonstrate that paraffin oil NEs and stearic acid SLNs are promising to be used as carriers of both lipophilic and amphiphilic drugs, including doxorubicin and thymoquinone. The accumulation of lipid nanoparticles with sizes smaller than 100 nm in cell nuclei is an advantage of such systems for the delivery of anticancer drugs, because this leads to DNA replication suppression followed by cell apoptosis.