Vol 80, No 4 (2018)

Communications devoted to analysis of the reasons and mechanisms for the formation of crystallization contacts between particles of disperse systems (primarily, NaCl) upon the removal of water from them and the contemporary methods for controlling this process with the purpose of preventing them from caking (loss of flowability) have been briefly reviewed. The main attention has been focused on works in which such processes are considered with the use of the methods and concepts of modern colloid chemistry and physicochemical mechanics of materials.

The drift velocity of a fractal cluster has been analyzed as depending on a parameter that characterizes its permeability. Equations have been derived that determine the range in which the conditions of the Stokes regime of cluster motion are met. Calculation results represented as the plots of the studied dependences have been discussed.

The coagulation kinetics of a monodisperse sol of Monosphere 250 silica in a 1.5 × 10^–1 М NaCl solution has been studied within a pH range of 2.0–6.2. The obtained results have been used to estimate the radius of action of the structural forces for interacting SiO₂ particles. It has been shown that, depending on the pH of a medium, the extension of boundary layers varies over a range of 4–8 nm, with the thickest boundary layers being observed near the point of zero charge of the particles.

Computer simulation of pyridine, pyridine-2-ol, and pyridine-2,5-diol solubilization by Span 80–water reverse micelles in n-decane has been performed. All solubilized compounds are polar (their polarity increases in a series pyridine, pyridine-2,5-diol, and pyridine-2-ol) and have different numbers of donors/acceptors forming hydrogen bonds. The most probable positions of pyridine molecules relative to a reverse micelle change fundamentally with a rise in the number of hydroxyl groups in their structure. Pyridine, pyridine-2-ol, and pyridine-2,5-diol are located in the nonpolar medium, on the micelle surface between the head groups of surfactant molecules, and on the inside surface of the aqueous core, respectively. Thus, the number and arrangement of hydrophilic groups in the structure of a molecule, rather than its polarity, have the strongest effect on the ability to solubilization in the reverse micelles.

Different methods have been proposed for the incorporation of a dye, vanadyl tetra-5,14,23,32-phenyl-2,3-naphthalocyanine, into the shells of polyelectrolyte capsules. Capsule preparation conditions have been selected to provide efficient incorporation of the dye and stability of capsules to aggregation. A suspension of the capsules has been irradiated with lasers operating at wavelengths belonging to the near-infrared spectral region. It has been found that the capsules can be disrupted under the irradiation. Continuous and pulsed laser radiations have been shown to have different effects on the capsules.

The effect of nanoparticles with different compositions and sizes on the rheological properties, filtration losses, and lubricating ability of drilling fluids has been experimentally studied. Nanoparticles of silicon, aluminum, and titanium oxides have been examined, while an aqueous bentonite suspension with a solid phase mass fraction of 5% has been used as a basic model of a drilling fluid. The concentrations and sizes of nanoparticles in the drilling fluids have been varied from 0.25 to 2 wt % and from 5 to 100 nm, respectively. It has been shown that the addition of nanoparticles substantially changes the properties of the drilling fluids. In contrast to suspensions of particles with macro- and microscopic sizes, the rheological parameters, filtration losses, and lubricating and sticking abilities of the suspensions containing nanoparticles depend on the size and nature of the latter and vary markedly already at low nanoparticle concentrations.

The grand canonical ensemble Monte Carlo method has been used to study adsorption of carbon dioxide, methane, and their mixtures with different compositions in slitlike carbon pores at a temperature of 318 K and pressures below 60 atm. The data obtained have been used to show the effect of fixed amounts of pre-adsorbed water (19, 37, and 70 vol %) on the adsorption capacity and selectivity of carbon micro- and mesopores. The presence of water reduces the adsorption capacity throughout the studied pressure range upon adsorption of gaseous mixtures containing less than 50% CO₂, as well as in narrow micropores (with widths of 8−12 Å). Upon adsorption of mixtures with CO₂ contents higher than 50%, the adsorption capacity of pores with low water contents appears, in some region of the isotherm, to be higher than that in dry pores. In the case of wide pores (16 and 20 Å), this region is located at low and moderate pressures, while for mesopores it is located at high pressures. The analysis of the calculated data has shown that the molecular mechanism of the influence of preadsorbed water on the adsorption capacity is based on the competition between the volume accessible for adsorption (decreases the capacity) and the strength of the interaction between carbon dioxide molecules and water molecules (increases the capacity). Therewith, the larger the surface area of the water–gas contact, the stronger the H₂O–CO₂ interactions.

The equilibrium, kinetics, and thermodynamics of adsorption of triarylmethane dye, crystalline violet, from aqueous solutions on Ca-montmorillonite have been studied. The regularities of the influence of the physicochemical parameters (suspension pH, clay and dye concentrations, temperature, and contact time) on the specific adsorption value of the dye have been found. It has been shown that Ca-montmorillonite is capable of removing the dye from aqueous solutions in a wide range of concentrations with an efficiency of up to 99.8%. The adsorption of crystalline violet obeys the Langmuir model (the correlation coefficient is 0.999), which corresponds to monolayer adsorption on a homogeneous surface. The kinetics of dye adsorption is described by a pseudo-second-order equation, which is characteristic of chemisorption. The thermodynamic parameters of adsorption, ΔH = 40.42 kJ/mol, ΔS = 139.6 J/mol, and ΔG =–4.68 kJ/mol (323 K), have been determined and lead to the conclusion that the dye adsorption is a spontaneous endothermic process.