Signature of jamming under steady shear in dense particulate suspensions
Abstract
Under an increasing applied shear stress (σ), viscosity of many dense particulate suspensions increases drastically beyond a stress onset (σ0), a phenomenon known as discontinuous shear-thickening (DST). Recent studies point out that some suspensions can transform into a stress induced solid-like shear jammed (SJ) state at high particle volume fraction (φ). SJ state develops a finite yield stress and hence is distinct from a shear-thickened state. Here, we study the steady state shear-thickening behaviour of dense suspensions formed by dispersing colloidal polystyrene particles (PS) in polyethylene glycol (PEG). We find that for small σ values the viscosity of the suspensions as a function of φ can be well described by Krieger-Dougherty (KD) relation. However, for higher values of σ (>> σ0), KD relation systematically overestimates the measured viscosity, particularly for higher φ values. This systematic deviation can be rationalized by the weakening of the sample due to flow induced failures of the solid-like SJ state. Using Wyart-Cates model, we propose a method to predict the SJ onset from the steady state rheology measurements. Our results are further supported by in-situ optical imaging of the sample boundary under shear.