Characterization of 2D colloids assembled by optically-induced electrohydrodynamics.

We report the results of a study characterizing the behavior of colloid aggregations under manipulation of a technique known as Rapid Electrokinetic Patterning (REP) - this technique is capable of dynamically manipulating the crystallinity of 2D colloid aggregations, potentially enabling dynamically tunable photonic crystals. Herein, aggregations of spherical polystyrene particles 1.0 μm in diameter suspended in a low conductivity aqueous solution were collected at the surface of an indium-tin oxide coated glass slide. The uniform AC field coupled with laser-induced heating produced electrothermal hydrodynamics which is responsible for the self-assembly characteristics of the planar colloidal aggregation. REP was characterized experimentally by analyzing the mutual particle spacing within the aggregation as a function of the AC signal and laser power. Numerical simulations justified the assumption that the primary forces responsible for colloidal patterning herein are Stokes drag forces and dipole-dipole repulsive forces.