Shear viscosity of concentrated spherical silica suspension – effect of polymethylsiloxane surface treatment

In determining the formulation of cosmetics dispersed in powder, it is very important to discover the rheological behavior of the suspension. In the case of concentrated particle suspension, it is known that the remarkable behavior of the rheology, which is different from the dilution system, is shown in ways such as shear thickening. In this report, the rheological behaviors of a concentrated spherical silica particle system were investigated in terms of particle–particle and particle–medium interaction. In the case of an aqueous medium, shear thickening occurred under certain conditions. It is noteworthy that the pH of an aqueous medium far from the isoelectric point (pH 4) of silica particles resulted in a decrease in shear viscosity η due to an increase in the double-layer repulsion. In addition, the rheological behaviors of suspension using the silica particles, which were treated with polydimethylsiloxane and methylhydrogen polysiloxane as the solvent system, were investigated. Shear thickening disappeared in all of the solvent systems, and polydimethylsiloxane system showed lower viscosity than the methylhydrogen polysiloxane system. The surface treatment, which affects the shear viscosity, is changed not only by the particle–particle interaction but also the particle–medium interaction.