Dynamics of colloids under periodic reversed sedimentation.

Motivated by the exploration of novel ways of assembling materials, we investigate a periodic reversed sedimentation protocol on micrometer-sized colloidal particles under sedimentation in a Hele-Shaw cell. The experiment consists in letting colloids sediment in a cell for a certain time before reversing the sedimentation by rotating the cell 180 degrees. Using direct stroboscope analysis imaging, the resulting strobe dynamics of the colloids is found to be strongly anisotropic. The equivalent diffusion coefficient, is extracted from the strobe dynamics analysis and is found to increase with colloids’ sedimentation time. We also show how the diffusion coefficient depends on the shape of sedimentation “cycle” that is applied. These results pave the path for novel methods of mixing grains and colloids in flows at low Reynolds numbers.