Effects of particle softness on shear thickening of microgel suspensions

A series of microgel particles composed of a polystyrene (PS) core and thermo-sensitive poly (N-isopropylacrylamide) (PNIPAM) shell with different shell thicknesses were investigated to elucidate the effect of microgel softness on its shear thickening behavior. Since the softness of the microgels increases with decreasing temperature through the volume phase transition effect of PNIPAM shell, the measured softness parameter, n, which is derived from the Zwanzig-Mountain equation, was used to measure and describe the combined influences of temperature and shell thickness. According to our results, the softness parameter is able to estimate the shear thickening behavior of microgel suspensions at least semi-quantitatively.