Three‐Dimensional Photomobility of Crosslinked Azobenzene Liquid‐Crystalline Polymer Fibers
Three‐Dimensional Photomobility of Crosslinked Azobenzene Liquid‐Crystalline Polymer Fibers
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DOI：
10.1002/adma.200902879
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发表时间：
2010-03
影响因子：
29.4
通讯作者：
Taiki Yoshino;M. Kondo;J. Mamiya;Motoi Kinoshita;Yanlei Yu;T. Ikeda
中科院分区：
文献类型：
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作者：
Taiki Yoshino;M. Kondo;J. Mamiya;Motoi Kinoshita;Yanlei Yu;T. Ikeda
人体骨骼肌由许多纤维束组成，其将化学能转化为机械功的关键功能是通过产生平稳运动和通过外部刺激诱导高应力来实现的。最近，已经有相当大的努力来开发可以模仿肌肉性能的人造肌肉或致动器，并且已经报道了类似于人类肌肉的各种材料，例如形状记忆合金，[1，2]聚合物凝胶，[3-5]导电聚合物，[6-8]碳纳米管，[9-12]和介电弹性体。[13]为了实现如人体肌肉中的平滑运动，最希望使用具有高机械柔性的软材料。交联液晶聚合物（CLCPs）是一种兼具液晶和弹性体特性的独特材料，由于液晶体系的自组织性质，在驱动器方面有着广阔的应用前景。[14-16]还报道了用于人造肌肉的以纤维形式对外部刺激作出反应的CLCP。[17-19]通过将诸如偶氮苯部分的光致变色分子引入CLCP，可以通过这些偶氮苯发色团的光化学反应诱导大的运动。[20-27]光驱动的软执行器可以在广泛的工业和医疗领域的新应用中发挥重要作用，因为光是一种清洁能源，可以快速远程控制。在我们以前的工作中，我们已经开发了含有偶氮苯部分的CLCPs的光致发光材料。[28-33]通过用UV光照射观察到仅由偶氮苯介晶组成的CLCP膜的弯曲。CLCP膜在暴露于UV光时可产生由LC的取向变化引起的表面变形，这有助于弯曲。我们还展示了CLCP及其复合材料仅由光驱动的新的三维运动：光驱动的塑料马达，尺蠖行走和灵活的机械臂运动。[34它们可以将光能直接转化为机械功，而无需电池、电线或齿轮的帮助。对于含有偶氮苯部分的CLCP纤维，可以预期LC介晶在暴露于UV光时的排列变化。在本通讯中，我们报告了CLCP光纤中光迁移率的精确方向控制。本研究中使用的LC单体（A6 AB 6和A6 AB 6 OH）和交联剂4，40-亚甲基双（苯基异氰酸酯）（MDI）的结构如图1a所示。根据与文献中类似的程序合成A6 AB 6。[36]CLCP纤维是通过两步反应制备的，如先前所报道的。[15]首先，通过自由基聚合使LC单体聚合。然后将所得共聚物与MDI混合，并通过将牙签的尖端浸入混合物中并用牙签尽可能快地牵拉混合物将混合物形成纤维。采用差示扫描量热法（DSC）、红外吸收光谱和偏光显微镜（POM）研究了CLCP纤维的热性能和光学性能。通过DSC测试，发现CLCP纤维的玻璃化转变温度（Tg）约为60 8 ℃。在CLCP纤维的IR光谱中，在约3500 cm-1处观察到对应于氨基甲酸酯键的NH 4 OH拉伸的吸收带。
Human skeletal muscles are composed of many bundles of fibers and their crucial function to convert chemical energy into mechanical work is achieved by generating smooth motion and inducing high stress by external stimuli. Recently, there has been a considerable effort to develop artificial muscles or actuators that can mimic muscle performance, and various materials that resemble human muscles have been reported such as shapememory alloys,[1, 2] polymer gels,[3–5] conducting polymers,[6–8] carbon nanotubes,[9–12] and dielectric elastomers.[13] To achieve smooth motion as in human muscles, it is most desirable to use soft materials with high mechanical flexibility. Crosslinked liquid-crystalline polymers (CLCPs) are unique materials with properties of both of liquid crystals (LCs) and elastomers and especially promising for applications in actuators due to the self-organization nature of LC systems.[14–16] CLCPs responding to external stimuli in the form of fibers were also reported for artificial muscles.[17–19] By incorporating photochromic molecules such as azobenzene moieties into CLCPs, large motions can be induced by photochemical reactions of these azobenzene chromophores.[20–27] Soft actuators driven by light could play an important role for novel applications in a wide range of industrial and medical fields, because light is a clean energy source and can be controlled rapidly and remotely. In our previous work, we have developed photomobile materials with CLCPs containing azobenzene moieties.[28–33] A bending of the CLCP films composed only of azobenzene mesogens has been observed by irradiation with UV light. The CLCP films can generate surface deformation caused by a change in alignment of LCs upon exposure to UV light, which contributes to the bending. We have also demonstrated new threedimensional movements of the CLCP and their composite materials driven only by light: a light-driven plastic motor, an inchworm walk, and a flexible robotic arm motion.[34, 35] They can convert light energy directly into mechanical work without the aid of batteries, electric wires, or gears. With CLCP fibers containing azobenzene moieties, one may expect the change in alignment of LC mesogens upon exposure to UV light. In this Communication, we report a precise directional control of photomobility in the CLCP fibers. We were able to induce three-dimensional movement of the CLCP fibers only by light.The structures of LC monomers (A6AB6 and A6AB6OH) and a crosslinker, 4, 40-methylenebis (phenyl isocyanate)(MDI) used in this study are shown in Figure 1a. A6AB6 was synthesized according to a procedure similar to that in the literature.[36] The CLCP fibers were prepared by two-step reactions, as previously reported.[15] Firstly, the LC monomers were polymerized by radical polymerization. Then the obtained copolymers were mixed with MDI, and the mixtures were formed into fibers by dipping a tip of a toothpick into the mixture and pulling the mixtures with the toothpick as quickly as possible. Thermal and optical properties of the CLCP fibers were investigated by differential scanning calorimetry (DSC), IR absorption spectroscopy, and polarizing optical microscopy (POM). By DSC measurements, it was found that the CLCP fibers exhibited a glass-transition temperature (Tg) of around 60 8C. In IR spectra of the CLCP fibers, the absorption band corresponding to the NÀH stretch of the urethane bond was observed at around 3500 cmÀ1.