Colloid Journal最新文献

Despite the significant interest of researchers, icing of aircraft, vehicles, ships, and equipment of offshore oil structures remains to be an urgent problem. This paper considers the factors that promote a decrease in the strength of the contact between ice and surfaces under an applied shear load. The main attention is focused on studying the influence of the rate of shear loading on the fracture of the interfacial contact between ice and superhydrophobic coatings. The strength of the adhesive contact under the conditions of controlled variations in the applied load is measured using a technique based on the detachment of ice from a surface under the influence of centrifugal force. The study is carried out for large ensembles of samples in the temperature range from −5 to −20°C, thereby making it possible to evaluate the influence of the quasi-liquid layer and the Rehbinder effect on a decrease in the shear adhesive strength. The results obtained indicate that the contact between ice and a superhydrophobic coating is fractured through a mixed viscous–brittle mechanism. In this case, a decrease in temperature or an increase in the loading rate causes a transition from the viscous to the brittle fracture. These results indicate a potential acceleration of ice shedding with an increase in the growth rate of the shear stress.

A procedure has been proposed for calculating the smallest possible thickness of the surface layer in a one-component liquid/saturated vapor system. A model of the layer homogeneous with respect to the pressure tensor has been considered. The smallest thickness of the surface layer and the molar volumes for the surface layer regions adjacent to the liquid and vapor phases have been calculated for liquid argon in the saturation line within a range from the triple point to almost critical temperature. Using published information as an example, it has been shown that the data on the distribution of the substance in the surface layer can be brought to the parameters of the proposed model.

The scientific community has preferred the photocatalysis process to remove organic pollutants from water. Many catalysts have been developed over the years, and one such catalyst is molybdenum disulfide (MoS₂), which is a two-dimensional (2D) material with an energy bandgap in the visible spectrum. In this manuscript, the facile synthesis of MoS₂ nanostructures in varying molybdenum (Mo) and sulphur (S), Mo/S ratios has been demonstrated through a single-pot hydrothermal route. The structural validation of the nanostructures was done using X-ray diffraction (XRD) patterns. Further, the morphological information about the MoS₂ nanostructures was gathered using the Field Emission Scanning Electron Microscope (FE-SEM) and High-Resolution Transmission Electron Microscope (HR-TEM) analyses. The photodegradation process of the Malachite Green dye was analyzed by UV-visible absorption spectroscopy. The results showed that 1T/2H MoS₂ nanoflowers degraded the malachite green dye with a degradation efficiency of 98.4%. The decomposition of this commonly used dye possesses great significance in industrial waste water treatment.

A systematic study has been performed for the effect of nonionic surfactants (NSs), i.e., ethoxylated higher fatty alcohols with different ethoxylation degrees, on the ultrasonic dispersion of carbon nanotubes in aqueous solutions and on the colloid-chemical properties of the resulting dispersions, namely, their optical density and the sizes and electrokinetic potentials of the particles in the colloidal systems. A non-linear dependence of the characteristics of dispersions on the ethoxylation degree has been revealed. This dependence is associated with structural transformations in NS molecules. The most efficient ethoxylation degree and concentration of nonionic surfactants in a solution, which have the highest disaggregating and stabilizing effects upon the preparation of carbon nanotube (CNT) dispersions, have been determined. The influence of the ethoxylation degree of the ethoxylated higher fatty alcohols on the electrokinetic properties of CNT dispersions has been revealed. It has been shown that carbon nanotube dispersions can be used to modify the rheological and electrical properties of gel systems based on rarely crosslinked poly(acrylic acid). The effects of NSs and CNTs on the viscosity, shear yield stress, consistency index, mechanical stability, relaxation time, and viscous flow activation energy of the polymer gels have been studied. It has been shown that the incorporation of nanotubes increases the electrical conductivity of the gels. The ultrastructure of the gel samples has been studied by transmission electron microscopy.

The article proposes a method for producing polyaniline-modified nanocomposite cryogel based on oxidized carbon nanotubes and reduced graphene oxide. Phenol–formaldehyde resin has been used as a crosslinking agent. Cryogel has been obtained by freeze drying in vacuum. Then, the material has been subjected to a post-processing, i.e., the carbonization in a tubular furnace. The obtained nanocomposite has been subjected to the comprehensive diagnostics by the methods of scanning and transmission electron microscopy, IR spectroscopy, X-ray diffraction analysis, and Raman spectroscopy. The parameters of the pore space have been estimated by nitrogen adsorption. It has been found that the carbonized nanocomposite cryogel is a mesoporous material with a specific surface area of 299 m²/g. IR and Raman spectra and X-ray diffraction patterns of the starting materials have been compared with the spectra of the carbonized cryogel. According to the results obtained, the nanocomposite exhibits peaks of all starting materials. The sorption capacity of the material has been evaluated by the example of the sorption of ions of a heavy metal, lead, from model aqueous solutions. Kinetic studies of adsorption in a limited volume have been carried out to determine the mechanism and time of the adsorption. It has been revealed that 99% of the contaminant is sorbed during the first 15 min, while an adsorption capacity of 295 mg/g is reached. The Elovich model, pseudo-first- and pseudo-second-order models, and an intradiffusion model have been employed to confirm the proposed adsorption mechanism.

Hydroxyapatite (HAp) nanoparticles organically modified with citrate group are fabricated via a simple wet chemical precipitation method. The as-synthesized nanoparticles are structurally characterized by TEM, XRD, FT-IR, EDAX and dynamic light scattering (DLS) to investigate in detail the influence of surface coating ligand i.e. citrate on HAp morphology, crystal structure, phase and colloidal stability of the particles. Production of single phase with hexagonal crystal structure is evident by XRD analysis. The work shows mesoporous structure could be synthesized under the influence of citrate as confirmed by TEM image and N₂ adsorption−desorption isotherm. The experimental results indicate that citrate strongly influences HAp crystallization giving reduced particle size and uniform distribution. BET and BJH analysis indicate large surface area 135.74 m²/g and pore diameter of 9.86 nm with a total pore volume of 0.41 cm³/g respectively for 1 : 1 citrate to calcium ion molar ratio. The appropriate surface area and pore entrance significantly indicate potentiality to apply into biomedical fields as drug loading/delivery application.

The self-assembly and gelation processes in low-concentrated aqueous solutions of L-cysteine and silver nitrate (cysteine–silver solution, CSS); low-molecular-weight water-soluble chitosan (CS); and a gelation initiator, CuSO₄, have been studied by various physicochemical methods, namely, UV spectroscopy, dynamic light scattering, pH-metry, viscometry, and scanning electron microscopy. It has been found that the gelation of CSS, which is used as a gel precursor, under the action of chitosan (CS) and copper sulfate occurs in a narrow concentration range: C_CH = 0.0100–0.0150 mg/mL, ({{C}_{{{text{CuS}}{{{text{O}}}_{{text{4}}}}}}}) = 0.4–0.6 mМ, C_L-cys = 3.00 mМ, and ({{C}_{{{text{AgN}}{{{text{O}}}_{{text{3}}}}}}}) = 3.75 mM, when Ag⁺/Cys molar ratio is 1.27. Hydrogels of various CSS–CS and CSS–CS–CuSO₄ compositions possess no high mechanical strength; however, they are stable in the course time. The structural elements of CSS, i.e., cluster chains of silver merchaptide (SM) zwitterions, are positively charged; therefore, no polyelectrolyte complexation occurs in CSS–CS and CSS–CS–CuSO₄ hydrogels, because the pH of CSS is 2.6. Addition of CuSO₄ to CSS–CS samples promotes the formation of a more strong hydrogel due to the association of SM clusters and CS molecules with sulfate anions and the coordination of Cu(II) ions with deprotonated carboxyl groups of different clusters.

The interaction of hen egg white lysozyme and block copolymers of poly(L–glutamic acid sodium salt) and polyethylene glycol (PGLU₁₀–PEG and PGLU₁₀₀–PEG) have been studied in an aqueous medium and at a water–air interface. Different physicochemical methods have been used: turbidimetry, tensiometry, fluorimetry, circular dichroism spectroscopy, electrophoretic light scattering, and transmission electron microscopy. The formation of mixed adsorption layers at the water–air interface has been observed at block copolymer : enzyme molar ratios of at most 2 : 1. In an aqueous medium, complexation of lysozyme with PGLU–PEG block copolymers leads to the formation of core–shell PGLU₁₀–PEG : lysozyme complexes and PGLU₁₀₀–PEG : lysozyme complexes with molar compositions of 1 : 1 or 2 : 1. The possibility of regulating the properties of the enzyme–block copolymer interaction products makes it possible to develop strategies for the production of antibacterial drugs.

Biodegradable solid-phase poly(vinyl alcohol)/carboxymethyl cellulose composites, which are promising to be used in pharmaceutics, agriculture, and chemical industry, have been obtained by an environmentally friendly method of “mild” mechanochemical activation without solvents and crosslinking agents. Air-dry mixtures of poly(vinyl alcohol) and carboxymethyl cellulose taken in mass ratios of 2 : 1, 1 : 1, and 1 : 2 have been subjected to a shock–shear action for 3 and 5 min (mechanical energy doses of 0.74 and 1.24 kJ/g) using an IVS-4 vibrating grinder (1500 rpm; 23.4 Hz; 0.55 kW; sample weight, 50 g; grinding bodies-to-sample mass ratio, 44 : 1). The mechanically activated samples in the form of medium powders (bulk density within a range of 600–1000 kg/m³) have been studied by the methods of scanning electron microscopy, differential scanning calorimetry, thermogravimetry, IR spectroscopy, optical microscopy, pycnometry, turbidimetry, and gravimetry. It has been found that the mechanochemical activation of an equimass mixture of poly(vinyl alcohol) and carboxymethyl cellulose at a mechanical energy dose of 1.24 kJ/g yields polymer solutions with a concentration of 1 g/dL that are rather transparent in the visible region (turbidity of 0.14 cm^–1) and stable for 96 h. It has been revealed that, when being dried at 25°C, poly(vinyl alcohol) crystallizes from aqueous 1 and 2 g/dL solutions to form dendrites or crystallites after treatment at mechanical energy doses of 0.74 and 1.24 kJ/g, respectively. Polymer films of the composites have a complex morphology that includes dendritic and axialite crystalline forms. It has been found that the mechanochemical treatment stimulates the formation of crystalline forms of polymers, changes their intermolecular interaction, and affects the hydroxyl and ether groups of carboxymethyl cellulose, as well as the hydroxyl groups of poly(vinyl alcohol).

Refractometric studies of hydrosols containing diamond nanoparticles have been carried out in this work. The samples for the study have been obtained from a statically synthesized diamond powder preliminarily subjected to standard purification by washing with strong acids and sonication. After additional repeated washing, centrifugation, sonication, and settling for a month, samples, whose particles contained different fractions of amorphous carbon, have been obtained. The particle size in the obtained samples was smaller than 100 nm. To analyze the data of refractometric measurements, equations have been derived that make it possible to determine the fraction of amorphous carbon in the particles and to calculate the thickness of its layer on the particle surface from the results of studying the refractive index and density of the sols of diamond particles. The data of the refractometric studies have been used to determine the ratios between the fractions of crystalline diamond and amorphous carbon in the particles. The performed studies have shown that the refractometric analysis of particle composition can be used to control the quality of industrially produced nanodiamonds.