光致形变液晶高分子

Photodeformable Liquid Crystal Polymers

交联液晶高分子兼具液晶的各向异性和高分子网络的弹性,并且具有优异的分子协同作用.在交联液晶高分子中引入光响应基团,例如偶氮苯后,即可赋予其光致形变性能,利用分子协同作用可以将光化学反应引起的分子结构变化放大为宏观形变,从而将光能直接转化成机械能.通过合理的分子结构和取向设计可以使液晶高分子产生诸如伸缩、弯曲、扭曲、振动等多种形式的光致形变,并用于各类光控柔性执行器件的构筑,在人工肌肉、微型机器人、微量液体操控等领域呈现出独特的优势和广阔的应用前景.本文总结和评述了光致形变液晶高分子的研究,包括材料结构对光致形变性能的影响、新型可加工光致形变材料的研究、利用可见光和近红外光触发形变的策略,以及光致形变液晶高分子微执行器在微量液体操控中的应用,最后展望了该领域的发展方向.

As a combination of polymer networks and liquid crystals, cross-linked liquid crystal polymers（CLCPs） exhibit unique properties such as elasticity, anisotropy, self-assembly and molecular cooperation effect. The most important point is that the orientation of liquid crystal（LC） mesogens is strongly coupled with the conformation of polymer backbones, thus change of LC arrangement by stimuli will generate shape change of the whole sample. The macroscopic deformation of CLCPs is reversible because the initial alignment of mesogens is memorized by network. Light is a particularly ideal stimulus since it is a clean energy with wide range of sources and can be precisely and conveniently manipulated in terms of wavelength, intensity and polarization direction. Incorporation of photochromic moieties, such as azobenzene moieties, into CLCPs enables photodeformation of the samples. The reversible trans-cis isomerization of azobenzenes upon specific light irradiation induces the change of LC order or LC director, and consequently leads to huge deformation of CLCPs. CLCPs containing azobenzene moieties can generate sophisticated movements including contraction/expansion, bending, oscillation and twisting, which directly convert photo energy into mechanical energy. Therefore, the photodeformable CLCPs are fabricated into various soft actuators by rational design, which brings about broad applications in artificial muscles, microrobots, microfluidics and so on. In this review, we mainly describe the development of azobenzene-containing CLCPs, and focus on the influence of molecular structures and alignment on the photodeformation behaviors. Started by introducing the mechanism of photodeformation involving photochemical phase transition and photoinduced reorientation, polyhydrosiloxane and polyacrylate CLCPs were described in details, with emphasis on the processable CLCPs and the novel methods to trigger deformation by visible light and infrared light. The applications of photodeformable CLCPs in the construction of diverse microscopic actuators ane microfluid manipulation are also described. An outlook of existing challenges and opportunities is also given at the end of this review.