The Rheological Properties of Suspensions Predicted by the Two-Step Structural Model

Abstract

The steady flow properties and rheopexy of suspensions have been calculated on the basis of the two-step structural model. In doing so, the following two assumptions have been adopted; (1) the structural parameter of the model is proportional to the viscosity of the system, and (2) the rate constants for the breaking of structure increase with increasing shear rate, while the rate constants for the structure formation are independent of shear rate.
A viscosity equation finally obtained is described by two characteristic rates of shear. These characteristic rates of shear correspond to the boundaries or transition points of the three typical regions found by us before. The rheopexy of suspensions strongly depends on a factor u, a function of rate constants of the kinetic model. The shear rate dependence of u is also characterized by the two characteristic rates of shear. Shearing stress at a constant rate of shear increases with increasing time either exponentially or sigmoidally depending upon shear rate showing a good agreement with experimental results obtained for suspensions of titanate fibers in polymer solutions.