MEASUREMENT OF THE DIFFUSION-COEFFICIENT OF STRONGLY INTERACTING COLLOIDAL SUSPENSIONS BY NONDEGENERATE 2-WAVE MIXING

We have measured the diffusion coefficient of strongly interacting "colloidal liquids" near the "liquid"-"solid" phase transition using nondegenerate two-wave mixing. We self-consistently calculate the diffusion coefficient as the product of the elastic modulus and a relaxation time that is identified as the time taken for a particle to diffuse one-tenth of the average interparticle distance. This procedure also predicts an electrolyte concentration where the diffusion coefficient vanishes, which is identified with the melting point of the colloidal crystal. This is shown to be essentially identical to the Lindemann criterion. In addition, we find that the colloidal liquid-solid transition as a function of ionic concentration gives a critical exponent gamma = 0.08 +/- 0.003.