Stress-structure relation in dense colloidal melt under forward and instantaneous reversal of shear

Abstract

Dense supercooled colloidal melt in forward shear from a quiescent state shows overshoot in shear stress at 10% strain with an unchanged fluid structure at equal stress before and after overshoot. In addition, we find overshoot in normal stress with a monotonic increase in osmotic pressure at an identical strain. The first and second normal stress become comparable in magnitude and opposite in sign. Functional dependence of the steady state stress and osmotic pressure with Peclet number demonstrate signature of crossover between Newtonian and nearly- Newtonian regime. Moreover, instantaneous shear reversal from steady state exhibit Bauschinger effect, where strong history dependence is observed depending on the time of flow reversal. The distribution of particulate stress and osmotic pressure at the point of flow reversal is shown to be a signature of the subsequent response. We link the history dependence of the stress-strain curves to changes in the fluid structure measured through the angular components of the radial distribution function. A uniform compression in transition from forward to reversed flowing state is found.