Inhomogeneous assembly of driven nematic colloids

Abstract

We present a quantitative analysis of the nonequilibrium assembly of colloidal particles dispersed ina nematic liquid crystal. The driven particles assemble into reconfigurable circular clusters by liquid-crystal-enabled electrokinetic phenomena generated by an AC electric field that provides propulsionalong the local director. We identify the coexistence of different aggregation states, including a central,jammed core, where short-range elastic attraction dominates, surrounded by a liquid-like corona whereparticles retain their mobility but reach a mechanical equilibrium that we rationalize in terms of abalance between centripetal phoretic drive and pairwise repulsion. An analysis of the compressibleliquid-like region reveals a linear density profile that can be tuned with the field frequency, and abond-orientational order that reaches a maximum at intermediate packing densities, where elasticeffects are minimized. Since the phoretic propulsion force acts also on assembled particles, wecompute the mechanical pressure and show that a hard-disk equation of state can be used to describethe assembly of this driven system.