Here, we present real-space studies of Brownian hard sphere transport though externally defined potential energy landscapes. Specifically, we examine how colloidal particles are re-routed as moderately dense suspensions pass through optical lattices, concentrating our attention upon the degree of sorting that occurs in multi-species flows. While methodologies reported elsewhere for microfluidic sorting of colloidal or biological matter employ active intervention to identify and selectively re-route particles one-by-one, the sorting described here is passive, with intrinsically parallel processing. In fact, the densities of co-flowing species examined here are sufficient to allow for significant many-body effects, which generally reduce the efficiencies of re-routing and sorting. We have studied four classes of transport phenomena, involving colloidal traffic within, respectively, a static lattice with a DC fluid flow, a continuously translating lattice with a DC fluid flow, a flashing lattice with AC fluid flow, and a flashing lattice with combined AC and DC fluid flow. We find that continuous lattice translation helps to reduce nearest neighbor particle distances, providing promise for efficiency improvements in future high throughput applications.
© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering.