Hydrogen Bond Enhances Photomechanical Swing of Liquid-Crystalline Polymer Bilayer Films
Hydrogen Bond Enhances Photomechanical Swing of Liquid-Crystalline Polymer Bilayer Films
复制标题
DOI：
10.1021/acsami.0c18449
复制
发表时间：
2021-01-29
影响因子：
9.5
通讯作者：
Yu, Haifeng
中科院分区：
文献类型：
--
作者：
Wang, Jianchuang;Huang, Shuai;Yu, Haifeng
机械摆动在自然界中是常见的，如声波、鸟类的翅膀跳动和心跳，这对于将输入能量转化为连续运动非常重要。在这里，我们报告了一种由市售的聚酰亚胺(Kapton)和含偶氮苯的液晶聚合物组成的光驱动摆动致动器。以不同摩尔比的含苯羧酸单体(M6BCOOH)和含偶氮苯单体(M(6)ABOC(2))为单体，通过共聚反应合成了以液晶聚合物为光活化层的聚合物。弹性模数高的Kapton层是光惰性的，起着衬底的作用。热退火后，薄膜在光化光连续照射下表现出混沌摆动。有趣的是，液晶聚合物薄膜中超分子氢键的存在大大提高了摆动幅度。M6BCOOH的引入加速了偶氮苯的反顺式光异构化反应。此外，它还形成氢键作为物理交联点，使聚合物膜能够作为一个整体工作。因此，它增强了光机械变形的驱动力。此外，它还提高了光活化层的弹性模量，并调节了双层带材的摆动行为。更重要的是，以酸性二聚体形式形成的氢键具有空间限制效应，延长了光驱动摆动的时间尺度。双层膜的光机械自振动可以归因于偶氮苯的光异构化过程和液晶聚合物的局部光软化效应的结合。
Mechanical swing is common in nature, such as sound waves, wingbeat of birds, and heartbeat, which is important to convert input energy into continuous motion. Here, we report a photodriven swing actuator composed of commercially available polyimide (Kapton) and azobenzene-containing liquid-crystalline polymers. The liquid-crystalline polymers act as the photoactive layer, which were synthesized by copolymerization of one benzenecarboxylic acid-containing monomer (M6BCOOH) and one azobenzene-containing monomer (M(6)ABOC(2)) with different molar ratios. The Kapton layer with a high elastic modulus is photoinert and functions as the substrate layer. After thermal annealing, the film displays chaotic swing under continuous irradiation of actinic light. Interestingly, the swing amplitude is greatly enhanced by the existence of supramolecular hydrogen bonding in liquid-crystalline polymer films. It is the introduction of M6BCOOH to the copolymer that accelerates the trans-cis photoisomerization rate of azobenzenes. Also, it forms a hydrogen bond as physical crosslinking sites, enabling the polymer film to work as a whole. Thus, it enhances the driving force for photomechanical deformation. Moreover, it improves the elastic modulus of the photoactive layer and modulates the swing behavior of the bilayer strip. More importantly, the formation of a hydrogen bond in the form of acidic dimers has a spatial confinement effect, extending the timescale of photodriven swing. The photomechanical self-vibration of the bilayer film can be ascribed to the combination of the photoisomerization process of azobenzenes with the local photosoftening effect of liquid-crystalline polymers.