Colloid Journal最新文献

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.

The formation of a fibrin film at the sites of cuts and wounds is a complex biochemical process that involves fibrinogen and thrombin as the main components, as well as other enzymes and proteins. Dynamic surface properties of adsorption films obtained from the solution, which contains factors VIII, XIIIa, von Willebrand factor and fibronectin, differ from the fibrinogen adsorption films and fibrin films obtained from a solution containing only fibrinogen and thrombin. Their dynamic surface elasticities exceed the corresponding values for fibrinogen (80 and 55 mN/m, respectively); however, they appear to be lower than value for fibrin prepared from pure components (115 mN/m). The surface pressures achieved for the adsorption films obtained from hemostatic glue (27 mN/m) exceed those for both aforementioned systems (14 mN/m). As follows from the Brewster angle microscopy and scanning electron microscopy data, significant changes in the morphology of the resulting films are responsible for the observed effect.

The work is devoted to the analysis of the nonlinear effects resulting from the influence of excess volumes of intergranular boundaries on the structure of segregations of impurity atoms in polycrystals. It is shown that the adsorption isotherm can describe the nonuniformities in the distribution of impurity atoms in the plane of an intergranular boundary. This suggests the existence of adsorption sites at the internal boundaries of polycrystals. It is proven that an excess volume of intergranular boundaries is the main parameter determining the magnitude of impurity segregations at the boundaries.

The objective of this study is to enhance the comprehension of the mechanism of enzymatic gelation in milk by investigating statistically significant changes in milk viscosity and carrying out corresponding electron microscopic studies of the process of structure formation at the enzymatic stage of coagulation using various enzyme preparations. Employing a non-destructive method (Hot-Wire) to monitor viscosity, we were able to confirm a decrease in viscosity during the middle of this stage and identify a previously undescribed peak in viscosity change at the end of the enzymatic stage. By conducting parallel studies utilizing transmission electron microscopy and various methods of specimen preparation, it was possible to discover that a hierarchical transformation process in the protein component of milk started at the end of the enzymatic stage of gelation in milk. This process is triggered by a cooperative conformational transition in casein micelle clusters, which leads to a series of increasingly energy-intensive reactions resulting in the transformation of loosely bound micelle clusters into denser aggregates. The final structure of the milk gel primarily consists of the previously formed individual micelle aggregates. It was noted that no changes in the microstructure of the milk gel were observed during the enzymatic stage of gelation when milk-clotting enzymes (MCEs) of animal, plant, and microbial (GMO) origins were used. Furthermore, investigations into the molecular weight distribution of soluble protein substances in samples generated with different types of MCEs revealed that the enzyme derived from the fungi of Rhizomucor miehei had a greater proteolytic effect on milk proteins compared to other variants of MCEs.

The viscoelastic properties and structure of solutions of mixed wormlike micelles based on a zwitterionic surfactant, oleylamidopropyldimethylcarboxybetaine (OAPB), and positively charged oleylamidopropyldimethylamine (OAPA) have been studied at different ratios between the components. At a small fraction of the cationic surfactant, OAPA, the solution exhibits viscoelastic properties characteristic of semidiluted solutions of entangled wormlike micelles, the presence of which has been confirmed by cryogenic electron microscopy data. It has been found that, as the molar fraction of the charged surfactant increases to 0.1, the viscosity and relaxation time of the solutions decrease by a factor of three, and the values of the storage modulus remain unchanged at short stress action times. The studied surfactants have a similar structure; therefore, when replacing zwitterionic OAPB molecules by positively charged OAPA molecules, the main factor of variations in the properties and structure is the enhancement of the electrostatic repulsion on the micelle surface. It has been shown that this factor leads to a decrease in the average length of micelles and an increase in their number, which have a weak effect on the rheological properties of the system as long as the length of the micelles is larger than the length of the subchains in the network. With an increase in the molar fraction of OAPA from 0.1 to 0.5, the viscosity and relaxation time drop drastically by several orders of magnitude and the viscoelastic response of the solution is lost; i.e., the network is destroyed. This transition from a semidilute solution to a dilute one is explained by a decrease in the length of the wormlike micelles and the formation of spherical ones. Cryogenic electron microscopy images have confirmed the formation of a mixture of long and short wormlike micelles with spherical micelles at an OAPA molar fraction of 0.5.

Coagulation of polydisperse detonation nanodiamond (DND) hydrosol containing primary aggregates with a prevailing average size in a range of 20–200 nm has been studied experimentally and theoretically within the framework of the classical and extended DLVO theory as depending on the concentrations of an indifferent electrolyte (NaCl) and potential-determining ions (pH). It has been shown that the surface of DND particles is charged due to the ionization of ionogenic amphoteric hydroxyl and acidic carboxyl groups located on it. The isoelectric point of the detonation nanodiamond particles has been found to correspond to pH 7.5. It has been revealed that the main stabilizing factor of the DND hydrosol is electrostatic. It has been shown that the stability and coagulation of the sol can be described within the framework of the extended DLVO theory using the effective Hamaker constant for primary porous aggregates and taking into account the initial polydispersity of the DND particles.

Polyimide films with molecular imprints of erythrosine and indigocarmine have been obtained. The structure and morphology of the film surfaces have been studied by scanning probe microscopy and IR spectroscopy. It has been found that the surface roughness of molecularly imprinted polymers (MIPs) increases, while the relief height amounts to 3–4 nm. The removal of template molecules leads to a redistribution of pores over sizes in the polymers with molecular imprints. The adsorption of dyes by MIP films has been carried out under static conditions. The degrees of extraction and the imprinting factors have been calculated for polymers with molecular imprints of the dyes. The high values of these parameters indicate the selectivity of MIPs to the target template molecules.