Collective action and entanglement of magnetically active liquid crystal elastomer ribbons

TL;DR

This study demonstrates how magnetic liquid crystal elastomer ribbons can self-assemble into reversible, mechanically tunable aggregates with potential applications in soft robotics and biomaterials.

Contribution

It introduces a new bio-inspired system of shape-morphing, magnetically responsive ribbons that can reversibly aggregate and disassemble, controlled by shape, temperature, and magnetic field.

Findings

Reversible aggregation depends on ribbon curvature and temperature.

Aggregates show up to 10^6 times increase in storage modulus.

Disassembly is controlled by magnetic field rotation speed.

Abstract

Interactions between active individuals in animal collectives lead to emergent responses that remain elusive in synthetic soft matter. Here, shape-morphing polymers are used to create bio-inspired transient solids that self-assemble with controlled mechanical properties and disassemble on demand. Dilute-suspensions of magnetic, heat-responsive liquid crystal elastomer ribbons mechanically interlock, inducing reversible aggregation. A mathematical model is developed that sheds light on the role of topological mechanisms in aggregation. Aggregation was favored for ribbons with moderate curvature at 25C above crosslinking temperature as compared to flat ribbons or higher curvature ribbons at higher temperatures. The ribbon suspensions reversibly transition between fluid- and solid-like states, exhibiting up to 6 orders-of-magnitude increase in the storage moduli of the entangled aggregates compared with the liquid dispersions. Controlled dissociation is induced by imparting kinetic energy to the individual ribbons at high magnetic field rotation speeds (> 200 RPM). Ribbon shape and the medium in which dissociation occurs were shown to govern disassembly. Imparting dynamic collective behaviors into synthetic systems may enable a range of potential applications from bio-inspired soft robotics to injectable biomaterials.