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Liquid crystal elastomers (LCEs) are made of liquid crystal molecules integrated with rubber-like polymer networks. An LCE exhibits both the thermotropic property of liquid crystals and the large deformation of elastomers. It can be monodomain or polydomain in the nematic phase and transforms to an isotropic phase at elevated temperature. These features have enabled various new applications of LCEs in robotics and other fields. However, despite substantial research and development in recent years, thermomechanical coupling in polydomain LCEs remains poorly studied, such as their temperature-dependent mechanical response and stretch-influenced isotropic-nematic phase transition. This knowledge gap severely limits the fundamental understanding of the structure-property relationship, as well as future developments of LCEs with precisely controlled material behaviors. Here, we construct a theoretical model to investigate the thermomechanical coupling in polydomain LCEs. The model includes a quasi-convex elastic energy of the polymer network and a free energy of mesogens. We study the working conditions where a polydomain LCE is subjected to various prescribed planar stretches and temperatures. The quasi-convex elastic energy enables a “mechanical phase diagram” that describes the macroscopic effective mechanical response of the material, and the free energy of mesogens governs their first-order nematic-isotropic phase transition. The evolution of the mechanical phase diagram and the order parameter with temperature is predicted and discussed. Unique temperature-dependent mechanical behaviors of the polydomain LCE that have never been reported before are shown in their stress-stretch curves. These results are hoped to motivate future fundamental studies and new applications of thermomechanical LCEs.
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This content will become publicly available on March 1, 2026
Synthesis-processing-property relationships in thermomechanics of liquid crystal elastomers
Liquid crystal elastomers (LCEs) are composed of rod-like liquid crystal (LC) molecules (mesogens) linked into elastomeric polymer networks. They present a nematic phase with directionally ordered mesogens at room temperature and an isotropic phase with no order at high temperatures, enabling large thermal-induced deformation. As a result, LCEs have become promising candidates for new applications in soft robotics and shape morphing. LCEs are being actively studied in both experiment and theory in recent years. However, the fundamental relationship among synthesis, processing, and thermomechanical behaviors of modern LCEs are still largely unclear. This knowledge gap is further complicated by the various LCE types, including polydomain, monodomain, nematic-genesis, and isotropic-genesis, each fabricated and used under different experimental conditions and applications. Here we explore synthesis-processing-property relationships in thermomechanics of various LCEs, by combining fabrication, characterization, and theoretical modeling. We adapt the widely used two-stage method to fabricate isotropic-genesis polydomain LCEs and nematic-genesis LCEs with varying pre-stretches during polymerization. We characterize the thermal-induced spontaneous deformation and the temperature-dependent uniaxial stress-stretch responses of the LCEs. We identify a new relationship among the soft elasticity, the thermal-induced spontaneous deformation, and the pre-stretch during polymerization, in the LCEs under study. Building on classical theories and our experimental results, we develop a constitutive model to describe the uniaxial behaviors of various LCEs. The theoretical predictions agree well with the experimental results on uniaxial stress-stretch responses at different temperatures. Finally, we discuss the remaining challenges and future opportunities in synthesis-processing-property relationships of LCEs.
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- Award ID(s):
- 2146409
- PAR ID:
- 10565349
- Publisher / Repository:
- Journal of the Mechanics and Physics of Solids
- Date Published:
- Journal Name:
- Journal of the Mechanics and Physics of Solids
- Volume:
- 196
- Issue:
- C
- ISSN:
- 0022-5096
- Page Range / eLocation ID:
- 105977
- Subject(s) / Keyword(s):
- liquid crystal elastomer synthesis-processing-property relationship thermomechanical coupling soft elasticity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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