Curling Liquid Crystal Microswimmers: a cascade of spontaneous symmetry breaking

TL;DR

This paper demonstrates curling and helical self-propulsion in nematic liquid crystal droplets driven by symmetry breaking, with controllable transitions between different motion states in aqueous emulsions.

Contribution

It reveals a new mechanism of spontaneous symmetry breaking causing curling and helical motion in liquid crystal microswimmers, including reversible phase-dependent behavior.

Findings

Nematic droplets self-propel in surfactant solutions above critical micelle concentration.

Coupling between nematic director and flow induces curling motion.

Auto-chemotaxis can spontaneously generate helical trajectories.

Abstract

We report curling self-propulsion in aqueous emulsions of common mesogenic compounds. Nematic liquid crystal droplets self-propel in a surfactant solution with concentrations above the critical micelle concentration while undergoing micellar solubilization. We analyzed trajectories both in a Hele-Shaw geometry and in a 3D setup at variable buoyancy. The coupling between the nematic director field and the convective flow inside the droplet leads to a second symmetry breaking which gives rise to curling motion in 2D. This is demonstrated through a reversible transition to non-helical persistent swimming by heating to the isotropic phase. Furthermore, auto-chemotaxis can spontaneously break the inversion symmetry, leading to helical trajectories.