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

Abstract

With a precision Haake RS1 rheometer, it is first found that at extremely low rates of shear (\( \dot \varepsilon \) ≤ 10−3 to 10−4 s−1 or lower), in nanodisperse systems based on highly dispersed aerosil or aerosil-bentonite compositions, with an increase in the shear rate, a non-Newtonian flow is observed. It is accompanied with a continuous growth of the effective viscosity of the dispersions ηeff, till the yield point P ≈ Pk is reached. At P ≥ Pk, the effective viscosity decreases abruptly; the structure decomposes via an aggregate mechanism. Earlier it was believed, that each viscosity level there corresponds to a combination of the full destruction of structural bonds and their partial restoring up to the equilibrium level determined by ηeff. In addition, the structured dispersed system flow remains Newtonian unless the static yield point has been overcome; it corresponds to the largest viscosity of a virtually undestructed system. Using a special procedure, SEM-imaging of the structure of the bentonite-suspension, as well as the bentonite added with minor amounts of aerosil, was carried out in water-ethanol medium. Photomicrographs of structure of the studied nanodisperse systems subject to shearing were obtained. The active filler (aerosil) particles distribution in the model system structure is studied. A procedure of studying the thixotropic properties of the structured nanodisperse systems in dynamic conditions is developed. The complex modeling of the structured nanodisperse system spreading over the scaled physical model, as well as special conditions of rheological tests in the Haake RS1 rotational rheometer cell, made us detecting a correlation between the spreading macroscopic factors and microscopic factors of the rheological behavior of the nanodisperse systems structure in dynamic conditions.