(565h) Liquid Crystals Enabled Electrokinetics

We demonstrate that spatially varying photo-patterned molecular orientation of liquid crystals combined with their anisotropic conductivity enables highly efficient liquid crystal-enabled electro-osmosis (LCEO) under the action of a uniform AC or DC electric field.  The effect is rooted in space charging of regions with varying molecular orientation imposed by the flat bounding surfaces.  The flow properties such as vorticity, symmetry, and amplitude are controlled by the predesigned photo-patterned surface alignment. The liquid crystal microfluidic cells are capable of pumping, mixing, reversal of flow direction, and transport of colloidal particles.  LCEO controlled by surface patterning is beneficial as compared to electro-osmosis and electrophoresis in isotropic electrolytes as the driving mechanisms are defined by the liquid crystalline medium and its surface alignment and are less sensitive to the properties of transported colloidal particles; in particular, the effect does not require metallic posts obstructing the flow.  These features might be beneficial for practical applications of liquid crystal electrokinetics.