Liquid crystal elastomers: an introduction and review of emerging technologies

Liquid crystal elastomers (LCEs) are a unique class of materials that combine rubber elasticity with liquid crystalline anisotropy to produce exceptional physical and optical properties such as actuation, soft elasticity, and birefringence. This review gives a brief overview of the physics behind liquid crystals and classifications of LCEs before discussing the methods traditionally used to synthesize LCEs, the new methods of synthesis that have emerged within the past several years, and the developing applications of LCEs. The review begins by discussing the organization of liquid crystals in LCEs and how their coupling to the polymer backbone affects their macroscopic properties. Traditional LCE synthesis methods and their drawbacks in terms of moving towards applications are then touched upon, as well as emerging chemistries that eliminate many of the challenges associated with LCE synthesis. Thiol-Michael reactions and covalent adaptable networks, which allow for bulk sample synthesis and repeated programming, respectively, are discussed at length. Finally, applications of LCEs in 4D printing and as biomedical devices are illustrated.