Reconfigurable interactions and three-dimensional patterning of colloidal particles and defects in lamellar soft media

TL;DR

This paper demonstrates how defects in cholesteric liquid crystals can be used to reconfigure and control the assembly of colloidal particles in three dimensions, enabling tunable and patterned mesoscopic structures.

Contribution

It introduces a method to manipulate defect-mediated interactions in cholesteric liquid crystals for reconfigurable colloidal assembly and patterning.

Findings

Colloids attract via elastic interactions when pinned to defect ends.

Optical manipulation can induce kinks in defects to control interactions.

Defect-particle interactions can be reconfigured to create desired patterns.

Abstract

Colloidal systems find important applications ranging from fabrication of photonic crystals to direct probing of phenomena typically encountered in atomic crystals and glasses. New applications - such as nanoantennas, plasmonic sensors, and nanocircuits - pose a challenge of achieving sparse colloidal assemblies with tunable interparticle separations that can be controlled at will. We demonstrate reconfigurable multiscale interactions and assembly of colloids mediated by defects in cholesteric liquid crystals that are probed by means of laser manipulation and three-dimensional imaging. We find that colloids attract via distance-independent elastic interactions when pinned to the ends of cholesteric oily streaks, line defects at which one or more layers are interrupted. However, dislocations and oily streaks can also be optically manipulated to induce kinks, allowing one to lock them into the desired configurations that are stabilized by elastic energy barriers for structural transformation of the particle-connecting defects. Under the influence of elastic energy landscape due to these defects, sublamellar-sized colloids self-assemble into structures mimicking the cores of dislocations and oily streaks. Interactions between these defect embedded colloids can be varied from attractive to repulsive by optically introducing dislocation kinks. The reconfigurable nature of defect-particle interactions allows for patterning of defects by manipulation of colloids and, in turn, patterning of particles by these defects, thus achieving desired colloidal configurations on scales ranging from the size of defect core to the sample size. This defect-colloidal sculpturing may be extended to other lamellar media, providing the means for optically guided self-assembly of mesoscopic composites with predesigned properties.