Thermomechanical Coupling in Polydomain Liquid Crystal Elastomers
Thermomechanical Coupling in Polydomain Liquid Crystal Elastomers
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多畴液晶弹性体的热-机械耦合
DOI：
10.1115/1.4063219
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发表时间：
2023-08
期刊：
影响因子：
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通讯作者：
Zhengxuan Wei;Peixun Wang;Ruobing Bai
中科院分区：
文献类型：
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作者：
Zhengxuan Wei;Peixun Wang;Ruobing Bai
液晶弹性体（LCE）由连接到橡胶状聚合物网络中的液晶分子制成。 LCE同时具有液晶的热致性质和弹性体的大变形特性。它可以是向列相的单畴或多畴，并在高温下转变为各向同性相。这些特性使得 LCE 在机器人和其他领域的各种应用成为可能。然而，尽管近年来进行了大量的研究和发展，但多域LCE中的热机械耦合仍然很少被研究，例如它们的温度依赖性机械响应和拉伸影响的各向同性向列相变。这种知识差距限制了对结构-性能关系的基本理解，以及具有精确控制材料行为的LCE的未来发展。在这里，我们构建了一个理论模型来研究多域LCE中的热机械耦合，其中包括聚合物网络的准凸弹性能和介晶的自由能。我们研究了多域 LCE 经受各种规定的平面拉伸和温度的工作条件。准凸弹性能使得“机械相图”能够描述材料的宏观有效机械响应，介晶的自由能控制其一阶向列-各向同性相变。预测并讨论了机械相图和序参数随温度的演变。以前从未报道过的多域 LCE 的温度依赖性机械行为显示在其应力-拉伸曲线中。这些结果有望推动热机械 LCE 的未来基础研究和应用。
Liquid crystal elastomers (LCEs) are made of liquid crystal molecules linked into rubber-like polymer networks. An LCE exhibits both the thermotropic property of liquid crystals and 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 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 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 thermomechanical coupling in polydomain LCEs, which includes a quasi-convex elastic energy of the polymer network and a free energy of mesogens. We study 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. Evolution of the mechanical phase diagram and the order parameter with temperature is predicted and discussed. 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 applications of thermomechanical LCEs.