A Photon Correlation Study of the Dynamics of Strongly Interacting Colloidal Systems: Colloidal Liquids and Colloidal Crystals

Abstract

Due to the strong electrostatic repulsion of Polystyrene latexes in water, these systems show shortrrange liquid-like order at low concentrations and long range, crystalline order at higher concentrations. Both phases were investigated by photon correlation spectroscopy. The first dynamic light scattering experiments on single crystals are reported. The dynamics of the colloidal liquids may be described by two diffusion coefficients for short and long times.This behaviour may be explained by a memory function formalism in a viscoelastic approximation. It is shown that the same formalism describes, in a purely elastic approximation, the colloidal crystals as well. The theory allows to extract information from the data on the elastic moduli and the sound velocities and, in the crystalline systems, a “phonon” dispersion, which yield, in principle, information on the particle interaction potential. The results on the crystals, however, may not be explained with a simple screened coulomb potential.For a more complete account of this work, see