Light scattering study of dynamic and time-averaged correlations in dispersions of charged particles

Several aqueous dispersions of charged polystyrene spheres (mean radius =250 aa) have been studied at very low ionic strength by conventional light scattering and photon correlation spectroscopy. Plotted as a function of scattering angle, the mean scattered intensity exhibited maxima similar to those found in the structure factor of simple liquids determined by X-ray or neutron scattering. Fourier transformation of the corrected intensity data yielded radial distribution functions whose structure indicated considerable short-range ordering of the particles due to repulsive coulombic interactions. The reciprocal of the effective particle diffusion coefficient (determined from the initial decay rate of the non-exponential temporal autocorrelation function of the scattered light field) showed angular dependence similar to the mean intensity, in agreement with recent theoretical predictions.