DYNAMICS AND SEDIMENTATION-VELOCITY IN CHARGE-STABILIZED COLLOIDAL SUSPENSIONS

Charge-stabilized suspensions are characterized by the strong electros tatic interactions between the particles so that rather dilute systems may exhibit strong correlation resulting in a well-developed short-ra nge order. This microstructure, quantitatively described by the pair d istribution function g(r), is rather different from that of (uncharged ) hard spheres. It is shown how this difference affects the ''hydrodyn amic function'' H(k), which appears in the expression for the first cu mulant Gamma(k) = k(2)D(eff)(k) = k(2)H(k)/S(k) of the dynamic autocor relation function. Without hydrodynamic interaction, H(k) = D-0, which is the free-diffusion coefficient. Using pairwise additive hydrodynam ic interaction and the lowest-order many-body theory of hydrodynamic i nteraction, it is found that H(k) can deviate considerably from D-0 ev en for systems of volume fractions phi as low as 10(-3). These effects are more pronounced for collective diffusion than for self-diffusion. Since H(k = 0) is closely related to the sedimentation velocity, we h ave studied this quantity as a function of volume fraction. It is foun d that (H(0)/D-0)-1 scales as phi(1/3) at low phi in salt-free suspens ions.