Colloid Journal最新文献

This study presents a rapid and eco-friendly approach to synthesize gold nanoparticles (AuNPs) using waste avocado seed extract (AV) as a reducing and capping agent. Microwave irradiation enables the synthesis of AuNPs within a minute, as evidenced by the solution’s characteristic red color and confirmed by a surface plasmon resonance (SPR) peak at ~530 nm in the UV-visible spectrum. Synthesis parameters, including pH and concentrations of AV and gold chloride, were optimized, revealing that mild alkaline conditions favor AuNP formation, while acidic conditions are detrimental. The AuNPs, characterized by transmission electron microscopy (TEM), exhibited a small size (9.9 ± 3.6 nm) and spherical morphology without aggregation. X-ray diffraction (XRD) confirmed the face-centered cubic (FCC) crystal structure of the AuNPs, and Fourier transform infrared (FTIR) spectroscopy indicated the involvement of functional groups in AV in the reduction and stabilization of the nanoparticles. The AV@AuNPs demonstrated excellent stability, as indicated by a high negative zeta potential (–27.0 ± 6.4 mV). Additionally, the nanoparticles showed strong antioxidant activity comparable to ascorbic acid and significant antibacterial efficacy against both Gram-positive (S. aureus and B. subtilis) and Gram-negative (E. coli and P. aeruginosa) bacteria, with a pronounced effect on Gram-negative strains.

Macroporous physical (noncovalent) cryogels have been prepared via freezing at –20°C for 12 h followed defrosting by heating at a rate of 0.03°C/min of aqueous poly(vinyl alcohol) (PVA) solutions without and with additives (0.1–0.5 mol/L) of basic α-amino acids (arginine, histidine, lysine, ornithine) in nonprotonated or salt forms, and the influence of such additives on the physicochemical properties of the gel materials formed in this way has been studied. It has been shown that additives of arginine, its hydrochloride, as well as histidine, exhibit a chaotropic action on the cryotropic gelation of PVA by hindering hydrogen bonding, thus leading to a decrease in the elasticity and heat endurance of the resultant cryogels, whereas additives of lysine, ornithine and their hydrochlorides, as well as histidine hydrochloride, act as kosmotropic agents causing an increase in the compressive elasticity modulus and the fusion temperature of the samples due to the promotion of hydrogen bonding. The kinetic study of releasing amino acid additives used in the work has shown that the hydrochlorides are released from a gel carrier into an external aqueous environment somewhat slower than are nonprotonated forms, but without noticeable diffusion hindrances in all cases. Taking into account that such amino acids are used in cosmetology, the results obtained in this study suggest that PVA cryogels loaded with amino acid additives may be of practical interest when developing carriers for cosmetics such as nourishing masks, coatings for problem areas of skin, “patches”, etc.

Water–salt solutions of interpolyelectrolyte complexes (IPECs) represent a classical example of “smart” systems, the phase equilibrium in which is regulated by many factors associated with both the parameters of the polymer components and the physical and chemical properties of an environment. This paper presents a model created on the basis of machine learning for predicting the region of existence of water-soluble IPECs. An approach is proposed for independent account of the physicochemical properties of polyelectrolytes and the properties of the environment. The developed model is universal and can be used to predict the properties of multicomponent systems of various chemical natures.

Composite films based on silver organosols stabilized with an anionic surfactant (AOT, sodium bis(2-ethylhexyl)sulfosuccinate) have been formed on polystyrene substrates by the dip-coating method. The process of film formation has been shown to be accompanied by the appearance of silver aggregates with interparticle distances exceeding the particle diameters. At the same time the aggregation has no effect on the optical properties of the nanoparticles. The obtained films exhibit plasmon absorption signal and the absence of plasmonic delocalization. Variations in the the number of substrate immersions in the sol makes it possible to affect the intensity of the plasmon absorption signal and the functional properties of the resulting coatings, such as their morphology, roughness (from 9 ± 2 to 25 ± 4 nm), thickness (from 585 ± 13 to 831 ± 28 nm), and the wettability of the surface by water (from 36 ± 6 to 53 ± 9°).

This study considers the potential of application of graphene-based nanofluids as heat-transfer agents in direct absorption solar collectors. It has been revealed that graphene-based nanofluids have superior absorption ability when interacting with monochromatic (520 nm) and near-IR radiation. As compared with distilled water, the use of graphene-based nanofluids as working fluids in direct absorption solar collectors increases their efficiency even at very low concentrations of dispersed phase particles. However, in order to apply graphene-based nanofluids as working fluids in energy systems, some issues need to be solved, primarily those related to their low stability and thermal instability.

A set of methods (tensiometry, conductometry, dynamic light scattering, spectroscopy, and fluorimetry) has been employed to study the self-assembly of long-chain bis-quaternized hydroxyethyl group-containing derivatives of 1,4-diazabicyclo[2.2.2]octane. The critical micelle concentrations, adsorption characteristics of the air–water interface, solubilization capacities with respect to poorly water-soluble OrangeOT dye, aggregation numbers, and sizes of aggregates have been determined. The influence of the structure (alkyl chain length and head group charge) of the studied compounds on their micelle-forming and antimicrobial properties, as well as hemolytic activity, has been determined.

Uniform rough films containing up to 73 at % silver have been obtained by the Doctor Blade method from concentrated silver nanoparticle organosols stabilized with sodium bis(2-ethylhexyl) sulfosuccinate. Variations in the wettability of the films have been studied in detail as depending on the conditions of their heat treatment within a temperature range of 50–500°C. The temperature dependence of the contact angles is not monotonic and implies the transition from superhydrophilic to weakly hydrophilic systems due to the processes of sintering of nanoparticles and thermal decomposition of the stabilizer. It has been experimentally shown that a transition from nonconductive to conductive coatings (from 500 to 105 mΩ/sq) is accompanied by a drastic increase in the contact angle (from 25 to 78°).

The electrostatic interaction between two identical charged dielectric spherical particles in a symmetric electrolyte solution has been studied on the basis of the Poisson–Boltzmann equation. Particular attention has been focused on the case of high surface potentials of the particles, whose radii are significantly larger than the Debye radius. Using the finite element method, the interaction forces between the particles have been calculated under the conditions of a uniform charge distribution on their surfaces and the absence of an external electric field. It has been shown that allowance for the nonlinearity of the Poisson–Boltzmann equation may be necessary even when the surface potentials of the particles are rather low and the formal application of the linearized Poisson–Boltzmann equation may be employed. The results obtained can be useful for understanding the processes that occur in colloidal systems and analyzing experimental data on the interaction of micron-sized particles in electrolyte solutions.

This study investigates the impact of homogenization parameters and the properties of the continuous phase of crude oils on the droplet size distribution, stability, and viscosity of emulsions composing it. Understanding these relationships is essential for enhancing the preparation and processing of several emulsion-based products, such as food, cosmetics, and pharmaceutical items. To achieve results, the study employed a measured experimental design to examine the effects of homogenization at speed (3000–12 000 rpm) in (3–9 min) on emulsions prepared of various continuous phases of crude oil. The droplet size distribution and viscosity of the crude oil emulsions were carefully measured and analyzed. Key findings demonstrate that increasing homogenization speed and time resulted in smaller droplet sizes and an increase in emulsion stability. Moreover, the continuous phase viscosity of crude oil affects both the droplet size and the viscosity of crude oil emulsion causing the larger droplets and higher emulsion viscosities due to an increase in continuous phase viscosity. Additionally, the study shows that the emulsion viscosity continuously increases over time (aging), indicating that it is suitable for long-term stability. The novelty of this work lies in its comprehensive exploration of the interconnected effects of homogenization parameters and continuous phase properties on emulsion characteristics. By providing insights into these relationships, the study contributes to a deeper understanding of emulsion behavior and offers valuable guidance for the development and optimization of emulsion-based products.

Neutral cationic red dye has been sorbed by Polysorb MP from a 0.25 mol/L AOT microemulsion in n-decane at different contents of the aqueous pseudophase. The maximum sorption capacity of the sorbent in the microemulsion is an order of magnitude higher than that in the water phase and amounts to 55 mg/g. A drastic drop in the degree of extraction upon increasing water content in the microemulsion from 1 to 8 vol % and the reversibility of the sorption processes have been revealed. Anionic dyes are not extracted by Polysorb in the same systems. As the water content increases, the zeta-potential of SiO₂ particles decreases from 18 to 1 mV. On the basis of the obtained dependencies, a cation-exchange mechanism has been proposed for the sorption from the microemulsion, with this mechanism involving the exchange of sodium and neutral red dye cations between micelles adsorbed on the surface of particles and micelles contained in the bulk of the microemulsion.