Dynamic light scattering and sedimentation experiments on silica dispersions at finite concentrations

We have performed photon correlation spectroscopy measurements on silica particles dispersed in cyclohexane. The diffusion coefficient D of the particles has been measured as a function of their volume fraction φ and could be described by D=D0(1+kDφ), where D0 is the diffusion coefficient at infinite dilution and the constant kD has a value of 1.3±0.2. This value is in agreement with the theoretical values of kD for hard spheres of Burgers, Batchelor, and Felderhof. These results have been compared with time averaged light scattering and sedimentation measurements. The time averaged light scattering experiments confirmed the hard sphere character of the particles earlier found by van Helden. The sedimentation constant has been measured as a function of the volume fraction of the particles resulting in a virial constant ks=6±1, which agrees with the theoretical values for hard spheres.