LINEAR VISCOELASTICITY OF COLLOIDAL MIXTURES

In this work we develop a unifying and general method for calculating linear viscoelastic properties of multicomponent colloidal mixtures of spherical particles. Using linear response theory based on the many-b ody Smoluchowski diffusion equation, we derive an exact expression for the zero shear rate shear relaxation function, together with a Green- Kubo formula for the static shear viscosity. From these results, we ob tain an exact expression for the high frequency elastic shear modulus of colloidal mixtures. We present, in addition, the first derivation o f a self-consistent mode coupling scheme for the linear viscoelasticit y of concentrated colloidal mixtures. This scheme offers the opportuni ty for a unified description of linear viscoelasticity and diffusion m echanisms, It accounts further for polydispersity and mixing effects, and leads naturally to a diverging shear viscosity at a glass transiti on point. Various limiting cases are considered to assess the accuracy of the approach. It is-shown to be a valuable method for evaluating t he rheological properties of concentrated colloidal mixtures. (C) 1998 American Institute of Physics.