Photomechanical effects of ferroelectric liquid-crystalline elastomers containing azobenzene chromophores.
Photomechanical effects of ferroelectric liquid-crystalline elastomers containing azobenzene chromophores.
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DOI：
10.1002/anie.200603053
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发表时间：
2007-01
影响因子：
--
通讯作者：
Yanlei Yu;T. Maeda;J. Mamiya;T. Ikeda
中科院分区：
文献类型：
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作者：
Yanlei Yu;T. Maeda;J. Mamiya;T. Ikeda
光致变形智能材料是一种能够在光的作用下发生形状或体积变化的新型材料。一方面，光是一种清洁能源，可以快速远程控制;另一方面，通过利用这些材料的变形，可以将光能直接转化为机械能（光机械效应）。大多数光致变形智能材料含有光致变色化合物，如偶氮苯，芪，螺吡喃。发色团在暴露于光时改变其分子结构;因此，它们掺入聚合物体系中引起聚合物链的构象变化以及伴随的聚合物溶液和固体的物理和化学性质通过光异构化的变化，包括橡胶网络和溶胀凝胶的光诱导收缩/膨胀。[1-12]然而，凝胶的低弹性模量和低屈服强度在致动性能方面提供了重要的限制，而对于固体聚合物网络，小于10%的变形限制了它们的实际应用。Finkelmann等人和其他研究小组通过将偶氮苯衍生物作为触发剂掺入液晶弹性体（LCE）中获得了大的光诱导收缩/膨胀。[13-15]具有聚合物网络的橡胶弹性的LCE表现出液晶（LC）相的同时各向异性取向对称性。它们的大的形状变化的驱动力被认为是由LC排列顺序的变化引起的：在用UV光照射时，含有偶氮苯发色团的LC体系经历排列顺序的降低，甚至由于偶氮苯部分的反式-顺式光异构化而发生LC-I相变，因为棒状反式偶氮苯部分稳定了LC排列，而弯曲的顺式结构降低了LC序参量。
Photodeformable smart materials that can undergo a shape or volume change in response to light are attracting increasing attention. On the one hand, light is a clean energy and can be controlled rapidly and remotely; on the other hand, by using the deformation of these materials, one can convert light energy into mechanical energy directly (photomechanical effects). Most photodeformable smart materials contain photochromic compounds, such as azobenzene, stilbene, and spiropyran. The chromophores change their molecular structure upon exposure to light; thus, their incorporation into polymer systems gives rise to conformation changes of the polymer chains and concomitant changes in the physical and chemical properties of the polymer solutions and solids through photoisomerization, including photoinduced contractions/expansions of rubbery networks and swollen gels.[1–12] However, the low elastic modulus and low yield strength of gels provide important limitations in the performance of actuation, while for the solid polymer networks, deformations of less than 10% limit their practical applications. Large photoinduced contractions/expansions have been acquired by Finkelmann et al. and other research groups by incorporating azobenzene derivatives into liquid-crystalline elastomers (LCEs) as a trigger.[13–15] LCEs with the rubber elasticity of polymer networks exhibit a simultaneous anisotropic orientational symmetry of liquid-crystalline (LC) phases. The driving force for their large changes in shape is suggested to arise from a variation of LC alignment order: upon irradiation with UV light, LC systems containing azobenzene chromophores experience a reduction in alignment order and even an LC-I phase transition as a result of the trans–cis photoisomerization of the azobenzene moieties, because the rodlike trans-azobenzene moieties stabilize the LC alignment, whereas the bent cis forms lower the LC order parameter.