Programmed liquid crystal elastomers with tunable actuation strain
The ability to program the local mechanical response of liquid crystalline polymer networks has been shown to generate complex mechanical responses. A facile two-step method to synthesize these anisotropic materials to realize either reversible or irreversible shape change behavior is reported. The first reaction is the addition of a nematic diacrylate to a primary amine to build macromers within a liquid crystal alignment cell. Subsequently, these macromers are crosslinked to trap the order of the liquid crystal into a crosslinked film. In unaligned samples, mechanical reorientation of the nematic director is used to isothermally program shapes at room temperature that can be recovered on heating. Under a load, the mechanically aligned materials exhibit tensile actuation behavior comparable to human skeletal muscle in stroke and specific work capacity. We also report spatially aligned films that reversibly morph from flat to a complex 3D shape with tunable strain from 3% to 55%.