Long time diffusion in suspensions of interacting charged colloids

Abstract

A new expression is given for the long time diffusion coefficient DL(k) of charged interacting colloidal spheres in suspension, as a function of the wavenumber k, near k = km, where the static structure factor has a maximum. The expression is based on a physical analogy between a mode description of the behaviour of atomic fluids (as observed in neutron scattering) and of colloids (as observed in light scattering). Use of this expresssion in conjunction with a hard-sphere model yields good agreement with extant data on colloids. The intermediate scattering function F(k,t), the spatial Fourier transform of the density- density correlation function of monodisperse colloidal spheres in suspension as measured by light scattering, can be represented reasonably well by the sum of two simple exponential decays respectively denning a short time and a long time collective diffusion process (1-5). The short time behaviour of F(k, i) is for times fB < t < ti