Viscoelastic properties of strongly flocculated polystyrene latex dispersions

Abstract

An investigation of the viscoelastic properties of a number of electrolyte-coagulated, concentrated polystyrene latex dispersions is described. Measurements of the continuous shear rheology, the true yield stress in shear and the creep compliance-derived modulus are presented and the influence of shear degradation effects on these properties is examined. The effect of prolonged shearing is to reduce significantly both the true and extrapolated Bingham yield stress and the shear modulus; the high shear differential viscosity is, however, largely unchanged. It is demonstrated that moduli derived from creep curves at the smallest measurable strains are in good agreement with those determined by pulse shearometry. At higher strains the shear modulus, measured well away from the linear viscoelastic regime, is significantly attenuated. A comparison with the degree of elastic recovery at these larger strains reveals that irreversible structural rearrangements are not the main source of this decrease. Rather the observed non-linear behaviour is in accord with the notion that large strains allow a different part of the inter-particle potential energy curve to be sampled.