Combining a liquid crystal elastomer (LCE) and a hydrogel opens a new avenue for the development of materials for soft actuators. Herein, we report a novel liquid crystalline hydrogel (LCH) consisting of a cross-linked main-chain LC polyester as the LCE and cross-linked poly(vinyl alcohol) (PVA) as the hydrogel, whose actuator, in contrast to existing main-chain LCE actuators, features perpendicular alignment of LC mesogens with respect to the stretching direction and exhibits positive thermal expansion in the stretching direction over the LC–isotropic phase transition. This peculiar actuating behavior arises from a reorientation process of mesogens, switching from parallel alignment right after stretching to perpendicular alignment after thermal equilibrium of the LCH in hot water followed by cooling, which appears to occur due to a rearrangement of the LCE domains during the thermal relaxation as well as the anisotropic swelling of the surrounding hydrogel domains and thus is unique to the LCH actuator. Unlike the hydrogel actuator, whose deformation is mostly based on a water-diffusion-induced volume change and thus is generally slow, the LCH actuator is driven by the order–disorder phase transition of mesogens and is much faster, with an actuation rate in seconds. Moreover, the LCH actuator not only brings together the reversible actuation of the LCE and the water-controlled shape memory effect of the PVA hydrogel but also is capable of optical welding, which facilitates the actuator design and fabrication.

中文翻译：

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液晶水凝胶致动器，在 Order-Disorder 相变上具有正热膨胀


将液晶弹性体 （LCE） 和水凝胶相结合，为软致动器材料的开发开辟了一条新途径。在此，我们报道了一种新型液晶水凝胶 （LCH），它由交联主链 LC 聚酯作为 LCE 和交联聚（乙烯醇）（PVA）作为水凝胶组成，其致动器与现有的主链 LCE 致动器相比，其致动器的特点是 LC 介生剂相对于拉伸方向垂直排列，并在 LC-各向同性相变上在拉伸方向上表现出正热膨胀。这种特殊的驱动行为源于中间原体的重新取向过程，在 LCH 在热水中达到热平衡后，从拉伸后的平行对齐切换到垂直对齐，然后冷却，这似乎是由于热弛豫期间 LCE 域的重新排列以及周围水凝胶域的各向异性膨胀而发生的，因此是 LCH 致动器所独有的。与水凝胶致动器不同，水凝胶致动器的变形主要基于水扩散引起的体积变化，因此通常很慢，而 LCH 致动器由介生体的有序无序相变驱动，并且速度要快得多，致动速率为秒。此外，LCH 致动器不仅将 LCE 的可逆致动和 PVA 水凝胶的水控形状记忆效应结合在一起，而且还能够进行光学焊接，从而促进致动器的设计和制造。