(560b) Placement and Separation of Colloids By Liquid Crystal Enabled Electrokinetics Controlled By Patterned Substrates

Colloids self-assemble into various organized superstructures determined by particle interactions. There is a tremendous progress in both the scientific understanding and applications of self-assemblies of single-type identical particles. Forming superstructures from two or more different types of particles and separating different species under fixed experimental conditions represent two major challenges of the current state-of-the art. Here we propose a versatile approach to direct heterogeneous self-assembly and separation of colloids using liquid crystals with spatially varying molecular orientation pre-imposed by substrate photoalignment and electrokinetic flows in these systems. Colloidal spheres that differ in surface properties (anchoring of the local director) are driven by the gradients of molecular orientation into different locations where they self-assemble through long-range elastic forces. An applied AC electric field separates the spheres according to their surface properties, by steering them into opposite directions through the effect of liquid crystal-enabled electrokinetics. Elastic forces responsible for heterogeneous assembly and separation are measured by exploring overdamped dynamics of the colloids. Control of colloidal self-assembly and sorting through patterned molecular orientation opens new opportunities for design of reconfigurable materials, microfluidics, lab-on-a-chip applications, targeted cargo delivery, biological sensing and sorting. The work is supported by NSF grants DMR-1507637, DMR-1121288 and DMS-1434185.