Study of the physicochemical characteristics of dispersions of n-alkanes C23H48 and C28H58 in water: zeta potential and temperatures of phase transitions

The effect of pH on the zeta potential of dispersions of individual n-alkanes C₂₃H₄₈ and C₂₈H₅₈ with particle sizes of the order of 100 nm, which were prepared by ultrasonic dispersion without the addition of surfactants, was studied. It is shown that at pH ranged from 4 to 12, the investigated n-alkanes form stable dispersions in water. They are characterized by a high zeta potential varying from ?30 to ?50 mV. The phase transition temperatures (melting point, crystallization temperature, formation of rotator phases) were determined for the dispersions using an optical method.

     

Formation and Properties of Microemulsions Stabilized by Ethoxylated Glycerides

Phase equilibrium in water-organic systems containing ethoxylated glycerides is studied. It is shown that microemulsions can be formed, and the domains of their existence are determined.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 328–332.Original Russian Text Copyright © 2005 by Gloukhova, Kienskaya, Myakon’kii, Kim.     

Synthesis and Some Properties of Sols Prepared by Hydrolysis of Lanthanum Nitrate

The procedure for synthesis of hydrosols by hydrolysis of lanthanum nitrate was developed. The range of pH values was established corresponding to the maximum aggregation stability of sols. The photon-correlation spectroscopy was applied to determine the average hydrodynamic radius of sol particles, equal to 50 nm. The thresholds of fast coagulation of sol in the presence of sodium nitrate and sodium sulfate were determined.     

Fabrication of rifampicin microcapsules with a polylactide shell

Procedure for encapsulation of rifampicin by evaporation of a volatile solvent was developed. An effective stabilizer making it possible to reach a 23% incorporation of the main substance into capsules was selected. The basic microcapsule parameters (particle size distribution, degree of polydispersity, and electrokinetic potential) were determined. The kinetics of rifampicin release from microcapsules was examined.     

Synthesis and Some Properties of Cerium Dioxide Hydrosols

Cerium dioxide hydrosols are synthesized by peptizing with nitric acid a precipitate obtained by hydrolyzing cerium(III) nitrate. The synthesized sols are stable with respect to aggregation in both acidic (pH 1.5–3.0) and alkaline media (pH 9.0–11.0). The mean hydrodynamic radius of particles is about 25 nm. The isoelectric point corresponds to pH 6.2. The phase composition of sol particles is determined by X-ray diffraction at pH of the dispersion medium ranging from 1.5 to 3.0. The sol coagulation thresholds are determined in the presence of sodium nitrate and sulfate, as well as of mixed magnesium salt at various pH values of the dispersion medium. Assumptions are made concerning the nature of the aggregative stability of sols.     

Synthesis and Some Colloidal Properties of Hydrosols Prepared by the Hydrolysis of Copper(II) Nitrate

The synthesis of hydrosols of copper(II) basic salts by the hydrolysis of copper(II) nitrate in the presence of ammonia was developed. A pH range and an optimal molar ratio [Cu²⁺] : [OH^–] = 1.1 : 1.0, at which hydrosols stable with respect to sedimentation were formed, were determined. The average hydrodynamic radius of dispersed phase particles ranging from 220 to 280 nm was measured by the photon correlation spectroscopy. It was shown that the hydrosols can be stabilized by poly(vinyl alcohol), and its optimal concentration providing their aggregation stability was determined. The thresholds of fast coagulation of the initial and stabilized hydrosols in the presence of potassium chloride and ammonium sulfate were found.     

Synthesis of hydrosols of oxygen-containing cobalt compounds

A procedure is developed for the synthesis of hydrosols of oxygen-containing cobalt compounds. The hydrosols are stable to aggregation for several weeks in the absence of additional stabilizers. It is established that the synthesized hydrosols contain crystalline particles formed from a mixture of CoO(OH) and Co₃O₄. According to transmission electron microscopy data, the most probable diameter of the particles is about 30 nm. The hydrosols are stable to aggregation at pH 6.2?C8.0. In this pH range, the particles are positively charged and the values of their electrokinetic potential are no higher than 10 mV.     

Synthesis of silver metal nanodispersions using Tollens reagent

It is shown that silver metal nanodispersions can be produced through the silver mirror reaction using the Tollens reagent in Aerosol OT-stabilized water-in-oil microemulsions using glucose as a reducing agent. The ranges of the formation of microemulsions and their droplet sizes, as well as component ratios and reaction conditions that yield stable nanodispersions, are determined.     

Effect of the synthesis temperature on some properties of aqueous dispersions of nanoparticles of oxygen-containing lanthanum compounds

The effect of the synthesis conditions of aqueous dispersions of oxygen-containing lanthanum compounds on the size, shape, and phase composition of nanoparticles is studied. It is established that the hydrolysis of lanthanum nitrate at the boiling point of a solution affords sols with a narrower particle size distribution and a higher degree of particle crystallinity. The ranges of [OH^?]/[La³⁺] concentration ratios are determined within which aggregatively stable aqueous dispersions of oxygen-containing lanthanum compounds can be synthesized.     

Synthesis and Use of Highly Dispersed Zinc Oxide

Methods for synthesis of zinc oxide hydrosols by peptization and condensation were developed. The basic colloid-chemical properties of the sols were determined: electrokinetic properties, size and phase composition of particles, and stability of hydrosols against introduction of electrolytes. The possibility of obtaining antibacterial and UV-protecting cosmetic preparations from the hydrosols obtained was demonstrated.