Shear thickening and microstructures of concentrated charge stabilized suspensions

Abstract

Rheological properties and microstructures of concentrated charge stabilized suspensions are studied in this dissertation. Suspensions containing monodispersed polystyrene particles with diameters ranging from 229 to 514 nm are used. Volume fractions ranged from 0.30 to 0.59 are studied. A non-equilibrium phase diagram of critical rheological properties and microstructures as function of shear rates is constructed for the first time. A parameter to measure the degree of suspension order under shear is established. The rapid increase of suspension viscosity as the shear rate increases is examined as function of volume fraction, previous shear history and the flow geometry.

Microstructures are studied using the small angle neutron scattering and the rheological measurements are obtained from both the constant stress and constant rate of strain rheometers. Dynamic variables such as the static yield stress, dynamic yield stress, catastrophic shear thinning stress and shear thickening stress are found to scale with the equilibrium modulus of the suspensions. Shear thickening is found to be dependent on the suspension's previous shear history and the size of the gap which bounds the suspension.