交联液晶聚合物光致形变及其柔性器件

Photoinduced deformation of crosslinked liquid crystalline polymers and soft actuators

光响应聚合物材料是指能够在光的作用下发生某些化学或物理反应,产生一系列结构和形态变化的功能聚合物材料.在光响应聚合物体系中引入液晶基元通过适度交联可形成光响应交联液晶聚合物,它结合了液晶的各向异性以及聚合物网络的橡胶弹性,具有优异的协同作用.且因为光能具有环保性、远程可控性、瞬时性等优异的特性,光响应交联液晶聚合物备受关注.通过合理的设计,光响应交联液晶聚合物可以实现全光驱动的形变,并且可以制成多种柔性智能执行器,在人工肌肉、微型机器人、微泵、传感器等仿生和智能微机械系统领域有着广泛的应用前景.本文综述了光响应交联液晶聚合物近年来的研究进展,包括其二维和三维形变、微观形变引起的表面形貌或其他性质的变化以及基于形变制成的柔性智能执行器,阐述了光响应的机理,并展望了该领域的发展前景.

Photoresponsive polymeric materials are a type of functional materials that can absorb photo energy and undergo intra- or inter-molecular physical or chemical reactions. As a result, the materials exhibit macroscopic property changes when exposed to light, such as shape, color or refractive index. They attract more and more attention for the reason that light is an environmental-friendly and remotely controllable stimulus source. Liquid crystals exhibit cooperative motion of molecules in changing the molecular alignment by external stimuli. That means that only a small amount of energy is needed to bring about the alignment change in the whole system. Crosslinked liquid crystalline polymers（CLCPs） can be prepared by crossliking conventional liquid crystal polymers into a network, which possess both the order of liquid crystals and the elasticity of elastomers. The cooperative effect of liquid crystals coupled with polymer network structure gives rise to the characteristic properties of CLCPs. The initial ordering of mesogens can be fixed by the crosslinkers in CLCPs, which might cause a quick change in shape due to a fast order-disorder transition. CLCPs have been a hot topic because large deformation can be induced by changing the alignment of mesogens in CLCPs by external stimuli such as electric fields, changes in temperature, humidity and light. Incorporation of photochromic moieties into CLCPs provides the materials with photo controllable properties. Photoresponsive CLCPs can generate sophisticated movements including contraction/expansion, bending and twisting which convert photo energy into mechanical energy directly. Therefore, the CLCPs can be fabricated into various soft smart actuators by rational design, which brings about broad applications in artificial muscles, microrobots, microvalves, sensors and so on. In this review, the photoresponsive mechanism is firstly elucidated involving photochemical phase transition and photo realignment. Then, we detail the historical development of photoresponsive CLCPs, with emphasis on lightdriven mechanical responses concerning two dimensional and three dimensional movements and surface property changes caused by deformation. We also summarize the recent progress of light-driven soft actuators made of photoresponsive CLCPs. We end with an outlook of existing challenges and opportunities.