Shear Thickening of Silica Rod Suspensions

Abstract

Colloidal particles in a liquid such as silica rod suspensions exhibit non-Newtonian behaviors like continuous shear thickening (CST) and discontinuous shear thickening (DST). These rheological behaviors of suspensions of spherical particles have been widely studied and abrupt shear thickening is known to be a result of the increasing interparticle frictional interactions with the increase of particle volume fraction and stress. These behaviors in suspensions of rod-like particles, however, have only recently been investigated due to the complexity of the rod-like particle suspensions under shear. While the role of the interparticle frictional forces has been explored, the contribution of the aspect ratio and size of the particles to shear thickening has mostly remained unknown. Here, we synthesize silica rods with a tunable aspect ratio in water/glycerol solution. We then perform rheological measurements to study the shear thickening behavior on several aspect ratios and sizes of the rod-like particles with various volume fractions. We demonstrate a decrease in the critical volume fraction for DST with increasing aspect ratio. With the Wyart and Cates model (W-C model), we can obtain the frictionless jamming fraction, ϕ_0, and the frictional jamming fraction, ϕ_m. We also investigate the effect of temperature on shear thickening and show that the flow curves of the relative viscosity under temperatures from 0 to 35 0C collapse onto a single curve.