Particle dynamics in dense suspensions flowing through microchannels

We will report on a systematic study, aimed at understanding the dynamics of colloidal hard spheres inside microfluidic channels. Real-time confocal microscopy is used to visualize the structure, diffusion and flow of model suspensions of 1 micron diameter silica spheres. By controlling the flow speed, we cover a range of Peclet numbers (<<1 and >>1) so we can study both the diffusion-controlled and the flow-controlled dynamics. Analysis of the apparent diffusion coefficient in the direction perpendicular to the flow reveals a clear spatial dependence of the diffusivity on the distance to the wall(s). While this is found both at low and at high Peclet numbers, the manifestations and underlying mechanisms are very different.