Transition from diffusive to subdiffusive motion in colloidal liquids.

In this work we report experimental and theoretical results for the motion of single colloidal particles embedded in complex fluids with different interparticle interactions. The motion of particles is found to follow a similar behavior for the different systems. In particular, the transition from the short-time diffusive motion to the subdiffusive intermediate-time motion is found to occur when the square root of its mean squared displacement is in the order of 1 tenth of the neighbors' interparticle distance, thus following a quantitative criterion similar to Lindemann's criterion for melting.

Hydrodynamic interactions between colloidal particles in a planar pore.

The correlation between the motion of pairs of colloidal particles confined in a planar pore is measured using optical microscopy. The systems studied here are aqueous suspensions of polystyrene spheres of diameter 1.9 µm, interacting as effective hard spheres, confined between two parallel planar plates separated by 2.9 µm. The lateral motion, along the plane parallel to the plates, of the particles is recorded with a time resolution of 30 frames s(-1). From the short-time motion, the hydrodynamic diffusion coefficients are determined as functions of the interparticle distance for various particle concentrations. At low concentrations, when the static correlation between particles is also low, the diffusion coefficients exhibit some symmetry, and at higher concentrations they are modulated by the structure of static correlation.