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.

中文翻译：

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液晶弹性体热力学中的合成-加工-性能关系


液晶弹性体 （LCE） 由连接到弹性聚合物网络中的棒状液晶 （LC） 分子 （mesogens） 组成。它们在室温下呈现具有方向有序介原的向列相，在高温下呈现无序的各向同相，从而实现较大的热诱导变形。因此，LCE 已成为软机器人和形状变形新应用的有希望的候选者。近年来，LCEs 在实验和理论方面都得到了积极的研究。然而，现代 LCE 的合成、加工和热机械行为之间的基本关系在很大程度上仍不清楚。各种 LCE 类型使这种知识差距进一步复杂化，包括多域、单域、向列发生和各向同性发生，每种类型都是在不同的实验条件和应用中制造和使用的。在这里，我们通过结合制造、表征和理论建模来探索各种 LCE 热力学中的合成-加工-性能关系。我们采用广泛使用的两阶段方法来制备在聚合过程中具有不同预拉伸的各向同性成因多域 LCE 和向列发生 LCE。我们表征了 LCE 的热诱导自发变形和温度依赖性的单轴应力拉伸响应。我们在所研究的 LCE 中确定了软弹性、热诱导自发变形和聚合过程中的预拉伸之间的新关系。基于经典理论和我们的实验结果，我们开发了一个本构模型来描述各种 LCE 的单轴行为。理论预测与不同温度下单轴应力-拉伸响应的实验结果吻合较好。 最后，我们讨论了 LCE 合成-加工-性能关系中的剩余挑战和未来机遇。