DYNAMICS AND SEDIMENTATION-VELOCITY IN CHARGE-STABILIZED COLLOIDAL SUSPENSIONS

Charge-stabilized suspensions are characterized by the strong electrostatic interactions between the particles so that rather dilute systems may exhibit strong correlation resulting in a well-developed short-range order. This microstructure, quantitatively described by the pair distribution function g(r), is rather different from that of (uncharged) hard spheres. It is shown how this difference affects the ''hydrodynamic function'' H(k), which appears in the expression for the first cumulant Gamma(k) = k(2)D(eff)(k) = k(2)H(k)/S(k) of the dynamic autocorrelation function. Without hydrodynamic interaction, H(k) = D-0, which is the free-diffusion coefficient. Using pairwise additive hydrodynamic interaction and the lowest-order many-body theory of hydrodynamic interaction, it is found that H(k) can deviate considerably from D-0 even 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 have studied this quantity as a function of volume fraction. It is found that (H(0)/D-0)-1 scales as phi(1/3) at low phi in salt-free suspensions.