Transient Response of Viscoelastic Concentrated Suspensions After Reversal in Large Amplitude Oscillatory Shear Flow

Concentrated suspensions of non-Brownian spheres dispersed in Newtonian / viscoelastic carrier liquids were placed under large amplitude oscillatory shear flows. Transient responses in shear rate and strain after each shear reversal were examined under sinusoidal stresses applied. The viscoelastic suspensions have showed similar transient responses with fluidity increase to those observed with Newtonian carrier liquids. It was considered that these responses were caused with collapse and rearrangement in the particulate microstructure. In order to clarify the influence of the viscoelasticity of carrier liquids on the fluidity increase, deviations in the shear rate from purely viscous predictions and characteristic strains were estimated. The flows of viscoelastic suspensions were reversed before stress reversal applied due to the elastic recoil of the polymers in the carrier liquid. Such kind of historical effects of viscoelasticity increased the fluidity at the first stage in the transient period and finished the whole transient phenomena with smaller strains. But, the viscoelasticity resisted the rearrangement in the latter half stage. Typical gap between the particles was introduced to obtain dependence of the volume fraction on the transient responses. The characteristic strains to the whole transient responses were normalized well with the gap both for Newtonian and viscoelastic cases.