Collective behavior of active topological solitons, knotted streamlines, and transport of cargo in liquid crystals

TL;DR

This paper investigates how topological solitons in liquid crystals can convert electric energy into directed motion, enabling cargo transport, with motion driven mainly by molecular rotational asymmetry rather than fluid flow asymmetry.

Contribution

It reveals the physical mechanisms behind reconfigurable soliton motion in liquid crystals and how topology influences their transport behavior.

Findings

Solitons can transport cargo along specific directions depending on electric field frequency.

Motion primarily results from molecular rotational asymmetry, not fluid flow.

Numerical models successfully reproduce soliton structures and dynamics.

Abstract

Active colloids and liquid crystals are capable of locally converting the macroscopically-supplied energy into directional motion and promise a host of new applications, ranging from drug delivery to cargo transport at the mesoscale. Here we uncover how topological solitons in liquid crystals can locally transform electric energy to translational motion and allow for the transport of cargo along directions dependent on frequency of the applied electric field. By combining polarized optical video microscopy and numerical modeling that reproduces both the equilibrium structures of solitons and their temporal evolution in applied fields, we uncover the physical underpinnings behind this reconfigurable motion and study how it depends on the structure and topology of solitons. We show that, unexpectedly, the directional motion of solitons with and without the cargo arises mainly from the asymmetry in rotational dynamics of molecular ordering in liquid crystal rather than from the asymmetry of fluid flows, as in conventional active soft matter systems.