Large-Scale Patterning and Dynamics of Topological Solitons in Chiral Nematic Liquid Crystals

The coexistence of order and fluidity in soft condensed matter often mimics that found in biological cells, which allows for complex collective dynamics and for highly technological applications, like displays and sensors. In active soft matter, different forms of emergent order can even arise because of this out-of-equilibrium dynamic behavior, powered by local energy conversion. We show that this emergent ordering can mimic behavior of familiar living systems with coherent motion, like crowds of people and schools of fish. Most active matter systems are biological in origin, although the discovery of inanimate, purely synthetic particles capable of such emergent behavior would enable new breeds of materials and nanomachines. Such examples are limited, typically with chemical or mechanical agitation sources of energy.

We show that thousands of particle-like topological solitons can exhibit collective dynamics while either (1) each converting macroscopically-supplied electric energy into motion along spontaneously-selected directions uncorrelated with the direction of electric field, (2) responding to photo-manipulation of the material’s elastic free energy landscape by changing shape or moving away from the light, or (3) a combination of the two. We demonstrate that these soliton dynamics occur in the absence of backflows, have the ability to carry cargo, display tunable dynamic self-assembly with their neighbors, possess long-range repulsive interactions, and exhibit emergent order and giant-number fluctuation scaling consistent with active systems such as schooling fish. We uncover how these topological solitons react to changes in the local and global elastic free energy, both in samples with flat geometries and spherical liquid crystal shells. We further show that skyrmions in motion can pack together as dense quasi-hexagonal crystallites and exhibit crowding and jamming behavior similar to crowds of people moving around obstacles.

Uniquely to our system, this plethora of emergent active behavior occurs in the absence of physical or biological particles and material flows, revealing the defining characteristics of the new field of solitonic active matter and promising many technological uses.