(591a) Anisotropic Diffusion in Concentrated Colloidal Dispersions: The Evanescent Diffusivity

We employ an analogy to traditional dynamic light scattering to describe the inhomogenous and anisotropic diffusion of colloid particles near a solid boundary measured via evanescent wave dynamic light scattering. Following this approach, new expressions are derived for the short-time self and collective diffusivities of a colloidal suspension of arbitrary volume fraction. Accelerated Stokesian dynamics simulations are used to calculate this evanescent-wave-diffusivity in the limit of large and small scattering wave numbers for a wide range of evanescent penetration depths. We show that at high volume fractions and larger penetration depths, the confinement has little effect on the dynamics of the suspension moving parallel to the wall. However, near and normal to the wall, the diffusivity shows a strong dependence on penetration depth for all volume fractions. This is due to the lubrication interactions between the particles and the boundary. These results are novel as well as comprehensive with respect to the range of penetration depth and volume fraction.