N. B. Ur’ev

Kinetics of structuring in the sol-gel systems based on tetraethoxysilane with organic additives: I. Sols

This paper reports on the results of rheological investigations into the kinetics of gelation of the sol-gel systems based on a water-alcohol solution of tetraethoxysilane (TEOS) modified by a number of metal salts and organic polyhydroxyl compounds, such as glycerol, poly(ethylene glycol) (PEG-300), and hyperbranched aliphatic complex polyol polyethers (HBP-49, HBP-64). It is demonstrated that, at a dispersed phase concentration of approximately 10 wt %, water-ethanol sol-gel systems containing 2–4 g/l of high-molecular additives possess a shear strength and are characterized by anomalous properties in their flow. The gelation time of sols in the presence of organic additives is affected by the ratio between the numbers of OH− hydrophilic and CH3 hydrophobic groups in the polymer molecule, the concentration of the introduced additive, and the electrolyte multivalence. The presence of metal salts enhances the structuring effect of polymers.

Macroscopic disruption of the continuity and stratified character of flow of structurized dispersions in shear flow

In this paper, concepts of the anisotropic nature of the flow of structured dispersions accompanied by disruption of a structure under continuous shear in layers oriented in the direction of shear flow are developed. The mechanism for the appearance and evolution of alternating solid and liquid fluid layers, together with disruption of the structure for cluster aggregates of particles of the dispersed phase, is shown experimentally, theoretically, and by computer simulation. The observed phenomena and those described in this paper significantly affect both the conditions for determination and description of rheological properties of structured dispersions and the technology of their production, processing, and formation of dispersed composite materials on their basis.

Increase in the Effective Viscosity of Nanodisperse Structured Systems in Shear Deformation at Extremely Low Rates

In this work, it was detected for the first time that, in the range that was previously deemed to be the range of the Newtonian viscosity η 0 , systems with lyophobic interactions of particles are characterized by a nonlinear dependence of the viscosity on the shear stress with an increase in the shear rates in the range 0 ≤ ≤ 10 –3 s –1 . The viscosity increases until the yield strength P k , after which an avalanche-like breakup of the structure starts. A specific feature of the flow of the considered structured dispersions in the range P < P k is that the viscosity increases in a sawtooth manner, which is typical of breakup of the structure into aggregates of particles with subsequent restoration and strengthening. This phenomenon can be explained by an increase in the probability of contacts between particles and aggregates of particles at lyophobic parts of the surface (if there is a lyophobic‐lyophilic mosaic pattern [5]). In this work, we studied suspensions of modified (methylated) nanodisperse Aerosil in mineral oil with concentrations of 2‐7 wt %. The total flow curves of the studied suspensions under quasi-equilibrium conditions were recorded with a Haake RS1 rotational rheometer in a controlled stress mode where the shear stress was specified discretely and the shear rate was controlled. Reaching of a quasi-equilibrium state at each point was detected by the device automatically once the amplitude of oscillations of a parameter being measured reached 1% of the mean. Great attention was paid to studying the behavior of structured nanodisperse systems in the range of extremely low shear rates e ˙ (on the order of 10 –6 s –1 ). Detailed data were obtained on the structural‐rheological properties of suspensions in the highest viscosity range characterizing the virtually unbroken structure of the system.

Minute deformations and nonlinear effects in nanodisperse structured systems

AbstractEver since P. A. Rebinder and his collaborators [1, 2, 4] published their article, it has been commonly accepted that in the range of minute deformation rates, the Newton character of a flow of structured disperse systems (pastes and suspensions) prevails. According to [1, 2], this region of viscosity is called the highest Newton viscosity of almost undisturbed structure, η0. In the present study, it was revealed that for, systems with lyophobic interactions between particles, in the region previously considered to be a region of Newton viscosity η0, a nonlinear dependence of the viscosity on shear stress is observed as the shear rate increases in the range

The detection of the effect of viscosity growth in nanodisperse systems during their shearing with ultralow rates

0 \leqslant \dot \varepsilon \leqslant 10^{ - 3} s^{ - 1}

Structure of adsorption layers and conformation transformations of ethylhydroxyethylcellulose on surfaces of titanium and iron oxides

. Thus, the viscosity increases up to the yield point Pk, at which point the avalanche decomposition of the structure begins, first into coarse aggregates and, subsequently, as their decomposition develops, into the smaller aggregates.

An IR study of the adsorption of ethylhydroxyethylcellulose on the surface of titanium and iron oxides under the action of mechanoactivation

This work describes a new class of macromolecular compounds, i.e., acrylic acid and isobornyl acrylate gradient block copolymers synthesized by controlled radical polymerization. A series of these gradient block copolymers was compared with acrylic acid and isobornyl acrylate block copolymers with similar compositions to demonstrate the effect of copolymer molecular architecture and the intense mechanical effect on their surface interactions with particles of different nature in aqueous dispersion systems. The method of electrokinetic sonic amplitude revealed the architectural effect of macromolecules to their surface interaction the particles at various concentrations of polymer and calculated the parameters of polymer adsorption layers. The surface interaction models were suggested for macromolecules of block and gradient block copolymers of various compositions with hydrophilic and hydrophobic particles and the copolymer architecture was proven to determine the nanostructure of polymer adsorption layers on interface. The nanostructural differences were suggested and confirmed in the interaction of block and gradient block copolymers with interface of different nature.

Simulation of structure formation in disperse systems

AbstractWith a precision Haake RS1 rheometer, it is first found that at extremely low rates of shear (