Control of colloidal placement by modulated molecular orientation in nematic cells

TL;DR

This paper presents a method to precisely position colloidal particles in nematic liquid crystals by using spatially patterned molecular orientations, enabling controlled self-assembly for advanced material design.

Contribution

It introduces a versatile technique to direct colloid placement via substrate photoalignment of nematic liquid crystals, leveraging elastic forces from molecular orientation gradients.

Findings

Colloids are driven to specific regions based on surface anchoring.

Elastic forces are quantified through overdamped dynamics.

Patterned molecular orientation enables controlled colloidal self-assembly.

Abstract

Colloids self-assemble into various organized superstructures determined by particle interactions. There is a tremendous progress in both the scientific understanding and applications of self-assemblies of single-type identical particles. Forming superstructures in which the colloidal particles occupy predesigned sites and remain in these sites despite thermal fluctuations represents a major challenge of the current state-of-the art. Here we propose a versatile approach to direct placement of colloids using nematic liquid crystals with spatially varying molecular orientation pre-imposed by substrate photoalignment. Colloidal particles in nematic environment are subject to the long-range elastic forces originating in the orientational order of the nematic. Gradients of the orientational order create an elastic energy landscape that drives the colloids into locations with preferred type of deformations. As an example, we demonstrate that colloidal spheres with perpendicular surface anchoring are driven into the regions of maximum splay, while spheres with tangential surface anchoring settle into the regions of bend. Elastic forces responsible for preferential placement are measured by exploring overdamped dynamics of the colloids. Control of colloidal self-assembly through patterned molecular orientation opens new opportunities for design of materials and devices in which particles should be placed in pre-designed locations.