Colloid Journal最新文献

The aim of this work is to find new ways to synthesize latexes (polymer suspensions) with a given size and surface structure of particles. The need for such latexes is not large-scale, but their development and production are extremely important for the development of high technologies. Monodisperse latexes are especially valuable in immunological diagnostics of a wide range of diseases. The article presents the results of studies of the nucleation of latex particles in a heterogeneous monomer−water system. The results of these studies made it possible to find conditions for the reproducible synthesis of monodisperse polystyrene latexes. In order to change the surface structure of latex particles, cetyl alcohol was dissolved in the initial monomer phase (styrene). The article presents the results of electron microscopic studies of the synthesized latexes. Nano crystals of this alcohol are clearly visible on the surface of the latex particles. It is suggested that, in deep monomer conversions, the process of crystallization of cetyl alcohol begins in polymer-monomer particles.

This work is devoted to studying the effect of an additional treatment of detonation nanodiamond (DND) powder of basic purification on the surface composition of DND particles, as well as their electrokinetic properties and aggregate stability in solutions of an indifferent electrolyte (NaCl) within a wide pH range. It has been found that an increase in the degree of purification and the number of protonated carboxyl groups on the surface of DND particles due to additional acidic and thermoammonia treatments leads to a shift in the position of the isoelectric point (IEP) from pH 7.0 for an initial sample to pH 6.3 and pH 6.0, respectively. It has been shown that the coagulation thresholds of the hydrosols at natural pH and the positions of stability zones in a 10^–3 M sodium chloride solution are in complete compliance with the IEP values. The highest thresholds values at pH 5.8 are observed for the initial DND, while, for the dispersion of DND particles subjected to the thermoammonia treatment, the fast coagulation occurs already at a concentration of 10^–4 M. It has also been found that the aggregate stability zones for additionally treated DND samples almost coincide with each other. For DND of basic purification, the stability zone expands in the region of positive zeta-potentials, while, in the region of negative values, no stability is observed, probably, due to the partial dissolution of surface impurities at high pH values and the transfer of their ionic forms to the solution, which causes coagulation of the DND particles.

The stabilization of bulk nanobubbles with a balance at their boundary of the Laplace pressure due to surface tension and electrostatic pressure due to Coulomb forces is considered. The presence of a hydrate layer of thickness ~1 nm with a tangential orientation of water dipoles around it is taken into account, the low permittivity of which, approximately equal to 3, increases the pressure at the boundary of the nanobubble. The dimensions and charge of a stable nanobubble are determined. It is shown that in salt water, the hydrate layer, regardless of the charge of the nanobubble, increases the pressure at its boundary by almost 30 times, and in fresh water—from 10 to 4 times.

Antibacterial coatings are used in the food, textile, and construction industries, as well as in biotechnology and medicine. This review considers the main types of coatings that prevent surfaces from fouling with biomacromolecules and microorganisms, i.e., anti-adhesive, contact-type, release-based, multifunctional, and intelligent (“smart”) coatings. For each type of the coatings, the most relevant and efficient active substances and their action mechanisms are described. Despite the wide use of anti-adhesive surfaces and contact-type coatings, they have many drawbacks that limit the scope of their application and reduce their activity and durability. Numerous studies have shown that multifunctional and intelligent coatings have a high potential for practical application and further studies of their modification aimed at producing universal and economically advantageous coatings. The main problem of the practical application of such surfaces is the imperfection of the methods used to assess the stability and antibacterial properties of the coatings under laboratory conditions.

This paper presents the results of a numerical simulation of an electrolyte solution behavior near a spherical dielectric microparticle covered with a homogeneous ion-selective shell under the influence of an external electric field. The particle is assumed to be stationary, and the electrolyte either stays still or is pumped externally with a constant velocity in absence of the electric field. The field, in turn, generates electroosmotic flow near the particle’s surface. It is shown that concentration polarization can occur near the particle, whereas electrokinetic instability only occurs near particles with a sufficiently thick shell. When the particle’s surface charge is opposite to the one of its shell, non-stationary regimes may be observed when the shell is thin enough.

A set of rheological equations based on structural-kinetic representations has been presented to describe viscous and elastic properties of structured liquids, namely, concentrated suspensions, emulsions, micellar solutions, and polymer solutions and melts. The structural model equations are valid for equilibrium stationary and equilibrium oscillating flows. The equations are suitable for approximating (tau (dot {gamma })), ({{N}_{1}}(dot {gamma })), (G{kern 1pt} ^{"}(omega )), and (G{kern 1pt} '(omega )) rheological curves in some intervals of shear rates or oscillation frequencies, with each interval corresponding to a certain state of a structure. The results of approximating shear viscosity curves for a polymer solution, a micellar solution, and an emulsion are presented as examples.

Porous crosslinked polyelectrolyte microspheres 1–5 μm in diameter have been synthesized on the basis of either p-styrene sulfonate used as a functional monomer or a mixture of p-styrene sulfonate and vinyl acetate. The content of sulfonate groups in the obtained polyelectrolyte microspheres is higher than 2 mmol/g. It has been shown that the incorporation of the hydrophobic comonomer significantly increases the swelling degree of the polyelectrolyte microspheres. The adsorption value of model compounds (fuchsine and methylene blue) has been found to significantly exceed the concentration of sulfonate groups. The morphology and structure of the surface layer of polyelectrolyte microspheres have been studied by optical and scanning electron microscopy and FTIR spectroscopy, while their specific surface area has been determined by the BET method.

The time dependences of the contact angles and the wetted surface spot diameters have been measured during the interaction between Co–Cu melts with copper contents of 20, 40, and 60 at % and graphite at temperatures of 1390, 1440, 1490, 1540, and 1590°C. Under these conditions, graphite is not wetted by the Co–Cu melts: the final contact angles for Co80–Cu20, Co60–Cu40, and Co40–Cu60 are 95, 110, and 100°, respectively. Therewith, the final diameters of the wetted surface spots somewhat increase. The metallographic analysis of the microstructure of the Co–Cu–C composite materials obtained by the contact alloying of Co–Cu melts with carbon has shown that the morphology of the structural components and the phase composition of the samples depend on the copper content. Composite materials (Co–27%C–10%Cu) + (Co–32%C–62%Cu) + C and (Co–19%C–15%Cu) + (Co–25%C–72%Cu) + C obtained by the interaction of the Co–Cu melts containing 20 and 40 at % copper with graphite have a macrohomogeneous structure.

Biosurfactants are one of the recently investigated biomolecules that have enormous applications in many fields including agriculture. As there is a need to develop less toxic, and environmentally friendly surfactants, therefore, amino acid-based biosurfactants that are produced from renewable raw materials are of great demand nowadays and can be used as an alternative to conventional chemical surfactants. The negative effects of chemical surfactants present in agrochemicals and modern detergents can damage human health and the environment, thus there is a crucial requirement to explore innovative, well planned, as well as cost-effective natural products for the welfare of humanity. Biodegradable surfactants created through green chemistry, specifically amino acid-based surfactants, are a favourable alternative to avoid these risks. Since amino acids (AAs) are inexhaustible compounds, therefore biosurfactants based on AAs have abundant potential as eco-friendly and environmentally friendly substances. Their higher biodegradation ability, low or even no toxicity, temperature stability, and tolerance to pH fluctuations make these biosurfactants preferable over chemical surfactants. In modern agriculture, most chemical pesticides and fertilizers used are frequently associated with numerous environmental issues. Hence, the development of green molecules as biosurfactants has a promising role in this regard to ensure agricultural sustainability. Biosurfactants can be harnessed for plant pathogen management, plant growth elevation, improving the quality of agricultural soil by soil remediation, degradation of complex hydrocarbons, increasing bioavailability of nutrients for advantageous plant-microbe interactions, and improving plant immunity, hence, they can supersede the grim synthetic surfactants which are presently being used.

The study examines the micellization of sodium dodecyl sulfate (SDS) with methylene blue (MB) in a propanol-water mixed solvent system within a temperature spanning from 298.15–313.15 K. The conductivity measurements of SDS-MB complex was carried out at 5, 10, and 15% volume fraction of propanol in water both in absence and presence of dye. The variation of CMC with temperature was analyzed to assess thermodynamic parameters of micellization. This approach offers valuable insights on the behavior of surfactant in mixed solvent system and sheds lights on different interactions occurring within the system. Spectrophotometric analysis was conducted to investigate the interactions between SDS-MB complex at 5, 10, and 15% volume fraction of propanol in aqueous medium. An increment in volume fraction of propanol hinders the process of micellization. However, in the presence of MB increases the efficiency of micellization and rendering the process more spontaneous. Consequently, MB monomers become associated with micelle which is the case of dye solubilization.