Hydrodynamic interactions in quasi-two-dimensional colloidal suspensions

Dynamical correlations between colloidal particles, in a quasi-two-dimensional geometry, are measured by optical microscopy. The system consists of charged polystyrene spheres suspended in water and confined between two parallel plates. The long-range electrostatic interaction is screened and the interparticle direct interaction becomes an effective excluded volume interaction. Thus, the observed long-range correlations, between the motion of pairs of particles, are due to the solvent mediated hydrodynamic interactions. Such correlations are observed as a dependence in the interparticle distance of the diffusion coefficients for the normal modes, collective and relative, for which results are presented here for a range of particle concentrations.