Characterization of 2D colloid aggregations created by optically induced electrohydrodynamics.

Rapid electrokinetic patterning (REP) is a technique for creating self-assembled monolayers (SAMs) of spherical particles in a liquid medium, and dynamically controlling them though the simultaneous application of an electric field and optically induced temperature gradients. Previous work has investigated and characterized REP axisymmetric aggregations generated from a focus laser within a uniform electric field; work herein characterizes line-shaped particle assemblies derived from the application of a linearly scanned laser. The resulting aggregations of spherical polystyrene particles (1 μm) suspended in low-conductivity aqueous potassium chloride solution (KCl, 2.5 mS/m) resembled elliptical-shaped crystalline geometries. The mean particle-to-particle spacing within the aggregation remained greater than 1.5 diameters for experiments herein (6.5 Vrms , 30 kHz) due to dipole-dipole repulsive forces. Interparticle spacing demonstrated a linear relationship (1.6-2.1 μm) with increasing scanning lengths (up to 83 μm), decreased from 1.9 to 1.7 μm with increasing scanning frequency (0.38-16 Hz) for a 53 μm scan length, and decreased from 2.0 to 1.6 μm with increasing laser power (11.9-18.8 mW) for a 59 μm, 16 Hz laser scan.