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.

Aggregative stability of a polydisperse zirconium oxide sol with average sizes of primary particles and aggregates equal to 24 and 95 nm, respectively, has been studied within a wide range of sodium chloride concentrations (3 × 10−3–1 M) by turbidimetry and dynamic light scattering. The experiments have been performed at pH 4.2 and 5.6, when sol particles are positively charged, and at pH 11, when they are negatively charged. The regions of weak and intense slow coagulation, as well as the region of fast coagulation, have been determined and characterized. It has been shown that, in most cases, the thresholds of the intense slow coagulation determined from the concentration dependences of the optical density and the average particle size coincide with each other within the experiment error. Assumptions have been brought out on the coagulation mechanism and its changes upon the passages between the coagulation regions, as well as on the role of the ratios between the particle sizes of separate fractions and their amounts in the sol.

Results of turbidimetry study of aggregate stability of binary SiO 2 –ZrО 2 sol and its components in 10 –3 –10 –1 M KCl solutions at рН 3.4 when ZrO 2 particles have a high positive charge and SiO 2 particles are slightly (close to zero) negatively charged are presented. The ratio of numerical concentrations of sol particles ZrO 2 to SiO 2 was 7.8 : 1. It was found that in binary SiO 2 –ZrО 2 sol both the process of heterocoagulation (mutual coagulation) of sols and coagulation of the same oxide particles occur throughout the studied range of KCl concentrations. The way of differentiation of processes of dissimilar SiO 2 and ZrO 2 particles heterocoagulation and coagulation of components is proposed. It is shown that at pH 3.4 the increase in the concentration of KCl solutions in binary SiO 2 –ZrО 2 sol leads to a decrease in the intensity of the process of ZrO 2 and SiO 2 particles mutual coagulation, which is explained by the decrease in the radius of action of attraction of dissimilar particles.

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.

Based on the results of studying the coagulation kinetics of monodisperse sol of SiO2 in NaCl solutions at various pH values, it is shown that the coagulation rate, flowing in the far potential minimum while maintaining a high repulsion barrier between the particles, depends on the formation and decomposition times of the aggregates. The boundary values of the depth and power of the far potential minimum-at the excess of which sol coagulates-are determined.

The influence of the concentration of potassium and barium chlorides on the aggregation stability of a hydrosol of monodisperse negatively charged detonation nanodiamond with particle sizes of 4−5 nm obtained by annealing of its agglomerates in air has been studied by turbidimetry. The experimental results have been discussed within the classical and generalized Derjaguin−Landau−Verwey−Overbeek theories. The analysis of the pair interaction potentials calculated for ultradispersed particles of detonation nanodiamond has led to the conclusion that the coagulation occurs by the barrier mechanism in the primary potential minimum. It has been assumed that the structural component of the interparticle interaction energy contributes to the total balance of the surface forces.

The results of the turbidimetric and dynamic light scattering study of colloid stability and coagulation kinetics of the polydisperse,gamma-Al2O3 hydrosol, prepared on the base of alumina nanopowder (Aeroxide Alu C, Evonik Degussa GmbH), in sodium chloride solutions (3 x 10(-2) M-2 M) at pH 4.2 are discussed within the extended Derjaguin-Landau-Verwey-Overbeek theory. We have revealed that the gamma-Al2O3 dispersion possess an anomalous stability, i.e. unusually high salt concentration is required to cause coagulation, and can be viewed as a pseudohydrophilic system. The observed aggregate sol stability has been attributed to both the structural component of the particle interaction energy and the interaction of the solvate layers formed due to the secondary hydration of the surface. In order to adjust the agreement of the experimental and theoretical results, we have determined the optimal structural component parameters and the effective Hamaker constants for aggregates containing in initial sol along with primary nanoparticles. By analyzing the calculated particle interaction energy profiles and stability factor values, we have concluded that coagulation mainly proceeds via the barrierless mechanism in the long-range potential minimum. (C) 2016 Elsevier B.V. All rights reserved.

The aggregation kinetics of OX50 sols in aqueous NaCl solutions (10–4–2 × 10–1 M) has been studied for 15 days or more by dynamic light scattering. The following set of characteristics has been considered to quantitatively estimate the coagulation intensity in the disperse systems: the particle size corresponding to the maximum in the differential particle size distribution curve, the height of the maximum, the polydispersity index, and the average diameter of the intensity distribution. It has been found that slow sol coagulation proceeds via the barrierless mechanism in secondary potential minimum, which arises from the predominance of the dispersion attractive forces over structural and electrostatic repulsive forces.

Методом фотометрии исследована кинетика агрегации монодисперсного золя кремнезема (средний размер частиц 220 нм, численная концентрация частиц n0 = 1010 см-3) в водных растворах NaCl и BaCl2 при рН = 6.2. Прямым методом поточной ультрамикроскопии исследована устойчивость разбавленного золя (n0 = 107 см-3) в растворах NaCl. Результаты проанализированы с позиции теории безбарьерной коагуляции Хогга–Янга и обратимой коагуляции Муллера. Установлено, что медленная коагуляция как концентрированного, так и разбавленного золя протекает по безбарьерному механизму в дальнем потенциальном минимуме.

A solvothermal method of sol–gel synthesis of anatase titania in solutions of anhydrous aliphatic acids in an autoclave at 250–350°С was developed. A series of mesoporous anatase powders were produced, which size, shape and phase composition are controlled by the organic acid radical length and synthesis temperature. The organic acid acts as solvent, reagent, and template agent in the formation of TiO2 nanocrystals. The powders show high activity towards the photocatalytic degradation of methylene blue (MB) in aqueous solutions, comparable with that of the reference Aeroxide P25 TiO2 nanopowder.

The aggregation kinetics of a monodisperse silica sol with an average particle size of 220 nm and particle number concentration n 0 = 1010 cm−3 in aqueous solutions of NaCl and BaCl2 at pH 6.2 is studied with the help of photometry. The stability of diluted sols (n 0 = 107 cm−3) in NaCl solutions is investigated by the direct method of flow ultramicroscopy. The results obtained are analyzed in terms of the theories of the Hogg-Yang barrierless coagulation and the Muller reversible coagulation. It is established that the slow coagulation of both concentrated and diluted sols proceeds via the barrierless mechanism in the secondary potential minimum.

Методом поточной ультрамикроскопии исследована кинетика агрегации монодисперсного золя кремнезема (размер частиц 220 нм) в водных растворах NaCl в интервале pH 2.0–10.2. Установлено, что медленная коагуляция золя протекает по безбарьерному механизму в дальнем потенциальном минимуме, возникающем в результате сложения дисперсионных сил притяжения и структурных сил отталкивания. Продемонстрировано влияние pH и концентрации NaCl на параметры структурной компоненты энергии взаимодействия частиц SiO2.

Photometric data on the aggregation stability of Al2O3 hydrosols prepared from Aeroxide Alu C nanopowder in NaCl solutions at pH 4.5 and 5.5 have been discussed within the framework of the generalized Derjaguin-Landau-Verwey-Overbeek theory. Analysis of the pair interaction potentials in an ensemble of particles of a sol primordially containing both primary nanoparticles and their aggregates has led to the conclusion that the coagulation proceeds via the barrierless mechanism in the secondary potential minimum.

Результаты фотометрического исследования агрегативной устойчивости гидрозоля Al2O3, приготовленного на основе нанопорошка “Aeroxide Alu C”, в растворах NaCl при рН 4.5 и 5.5 обсуждены в рамках обобщенной теории Дерягина–Ландау–Фервея–Овербека. На основе анализа парных потенциалов взаимодействия в ансамбле частиц золя, содержащего изначально как первичные наночастицы, так и агрегаты наночастиц, сделан вывод о протекании коагуляции по безбарьерному механизму в дальнем потенциальном минимуме.