Magnetically responsive gourd-shaped colloidal particles in cholesteric liquid crystals

TL;DR

This study explores how magnetically responsive gourd-shaped colloidal particles behave in cholesteric liquid crystals, revealing complex interactions, metastable states, and new assembly methods influenced by particle shape, chirality, and magnetic manipulation.

Contribution

It introduces the use of magnetically responsive gourd-shaped colloids in cholesterics, demonstrating non-monotonic interactions, metastable levels, and laser-assisted assembly techniques.

Findings

Non-monotonic, oscillatory particle-wall interactions.

Multiple metastable sedimentation levels.

Laser tweezers enable 3D assembly of particles.

Abstract

Particle shape and medium chirality are two key features recently used to control anisotropic colloidal self-assembly and dynamics in liquid crystals. Here, we study magnetically responsive gourd-shaped colloidal particles dispersed in cholesteric liquid crystals with periodicity comparable or smaller than the particle's dimensions. Using magnetic manipulation and optical tweezers, which allow one to position colloids near the confining walls, we measured the elastic repulsive interactions of these particles with confining surfaces and found that separation-dependent particle-wall interaction force is a non-monotonic function of separation and shows oscillatory behavior. We show that gourd-shaped particles in cholesterics reside not on a single sedimentation level, but on multiple long-lived metastable levels separated by a distance comparable to cholesteric periodicity. Finally, we demonstrate three-dimensional laser tweezers assisted assembly of gourd-shaped particles taking advantage of both orientational order and twist periodicity of cholesterics, potentially allowing new forms of orientationally and positionally ordered colloidal organization in these media.