Models for normal stress and orientational order in sheared kaolin suspensions

Abstract

At low pH-values, concentrated kaolin suspensions at rest appear as isotropic gels of disordered platelike particles. An X-ray diffraction technique applied to shock frozen samples suggests that a shear flow produces a nematiclike alignment of the kaolinite platelets. The orientational order parameter of the nematic alignment was found to be relative small. Rheological models based on the theory for nematic polymers are proposed to explain the observed negative first normal stress difference. The models also provide us a description of the positive first normal stress difference of kaolin suspensions found at high pH-values.