Concentration dependence of the self-diffusion coefficient of hard, spherical particles measured with photon correlation spectroscopy

Abstract

The concentration dependence of the self-diffusion coefficient Ds has been measured with photon correlation spectroscopy (PCS) from a mixture of two optically distinct hard spherical silica particles in cycloheptane. In the long wavelength limit (K=0), we have found that Ds is a linear function of the particle volume fraction φ in the range of 0<φ<0.10: Ds(K=0)=D0(1+kD,sφ). Here, D0 is the diffusion coefficient at infinite dilution and the constant kD,s has an experimental value of −2.7±0.3. Away from the optical matching point of one of the components and close to that of the other component, we have shown that the theories of optical polydispersity can be applied in light scattering and it is found that the result of the PCS measurements is in accordance with that obtained from time-averaged light scattering. With the ultracentrifugation techique, it was possible to obtain information about the sedimentation velocity of a few ‘‘tracer’’ particles in the presence of other particles. Here, we found that the experimental data are not consistent with the available theories.