Colloid Journal最新文献

Using dark-field hyperspectral microscopy, we analyzed the distribution of fluorescently-labelled polystyrene microspheres with a size of 2 μm in mosquito larvae and observed the quenching of fluorescence and changes in spectral properties due to histological processing. We propose enhanced dark-field microscopy coupled with hyperspectral imaging as a versatile method for analysing polymer colloids (microplastics) biodistribution in complex tissues.

This paper reports on the successful preparation of a series of ZnO–Ag₂O nanocomposite crystals with varying elemental contents by a novel oil−water interface method. The structures, compositions, microscopic morphologies, and optical properties of these crystals were characterized using HRTEM, SEM, XRD, EDX, XPS, UV-Vis, and PL measurements. The obtained well-dispersed hetero-structure nanocomposite crystals, with a particle size mainly ranged from 50 to 100 nm and a high purity, displayed a good absorption ability in the visible region. Virtually, the nanocomposite crystals exhibited a significant red-shift 5–15 nm in the UV diffuse absorption edge towards the visible range, accompanied by a substantial reduction in fluorescence absorption intensity. Importantly, the photocatalytic degradation of these nanocomposites was tested against Congo red (CR) dye under visible light excitation. The results revealed that the degradation efficiencies of ZnO–Ag₂O nanocomposite crystals against CR under visible light were 9.4 and 2.7 times as high as those of pure ZnO and Ag₂O nanoparticles, respectively. Also, the antimicrobial function of ZnO–Ag₂O nanocomposite crystals was tested against harmful bacteria. The study results indicated that the diameters of inhibition zone of the nanocomposite crystals were respectively 13.5 mm for Gram-negative Escherichia coli and 12.9 mm for Gram-positive Bacillus subtilis, significantly larger than that of pure ZnO due to the synergistic effects of ZnO and Ag₂O nanoparticles. The high photocatalytic efficiency and strong antimicrobial activity of ZnO–Ag₂O nanocomposite crystals suggest their great significance in degrading pollutants and killing harmful bacteria.

The magnetization reversal kinetics has been theoretically considered for a nanosized ferromagnetic particle in a soft viscoelastic medium. In contrast to well-known works, we have considered the simultaneous action of the Néel mechanism of magnetization reversal of a particle (overcoming the potential barrier of magnetic anisotropy by its magnetic moment), and rotation (turn) of the particle body as a result of a change in the external magnetic field. The case of a high magnetic anisotropy of the particle is considered, i.e., it has been assumed that its energy significantly exceeds the thermal energy of the system and the energy of the interaction between the particle and the magnetic field. No other limitations have been imposed on field strength. The case of low fields has been considered in greater detail in the linear approximation of the dependence of magnetization on the field. The components of the complex susceptibility of the composite are calculated within the framework of this approximation. It has been shown that the real component of the susceptibility decreases monotonically with the field frequency. If the stiffness of the composite is high or low, the imaginary component has one maximum, which corresponds to the Néel mechanism of magnetization reversal or particle rotation in a viscoelastic medium, respectively. At intermediate values of composite stiffness, the frequency dependence of the imaginary susceptibility has two maxima.

Polyelectrolyte complexes of chitosan (ChTS) with κ-carrageenan (CARR) have been obtained and characterized as potential adsorbents of fluorescein (FLC) nanomarker in aqueous media at different pH values. The binding of FLC to ChTS and the κ-CARR–ChTS complex has been studied by spectroscopic methods. The efficiency and mechanism of fluorone dye adsorption on the synthesized complexes have been investigated by analyzing equilibrium adsorption isotherms. The isotherm of FLC adsorption on particles of the polyelectrolyte complex has been adequately described within the framework of the Freundlich model. Data on fluorescence quenching have been used to determine the effective Stern–Volmer constants of FLC with ChTS and the κ-CARR–ChTS complex and to show that the nanomarker is bound to biopolymers via different interaction mechanisms.

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.