Liquid crystal elastomers: an introduction and review of emerging technologies

ABSTRACT

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.

KEYWORDS:

• Liquid crystal elastomer
• main-chain LCE
• click chemistry
• covalent adaptable network
• 4D printing

Acknowledgements

Research was sponsored by the Army Research Office and was accomplished under Grant Number 125786. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either express or implied, of the Army Research Officer or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. Additionally, this work was also supported under NSF CAREER Award CMMI-1350436. The authors would also like to thank Montucky Cold Snacks for sponsoring their research lab.

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In accordance with Taylor & Francis policy, it is being reported that the corresponding author of this publication has equity in a company that may be affected by the research reported in the enclosed paper. Those interests have been fully disclosed to Taylor & Francis.

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Funding

This material is based upon work supported by, or in part by, the U.S. Army Research Laboratory and the U. S. Army Research Office under [Grant Number W911NF1710165]; National Science Foundation: [Grant Number CMMI-1350436].