Photoinduced Deformation of Crosslinked Liquid-Crystalline Polymer Film Oriented by a Highly Aligned Carbon Nanotube Sheet
Photoinduced Deformation of Crosslinked Liquid-Crystalline Polymer Film Oriented by a Highly Aligned Carbon Nanotube Sheet
复制标题
高度排列碳纳米管片定向交联液晶聚合物薄膜的光致变形
DOI：
10.1002/anie.201200723
复制
发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Yu, Yanlei
中科院分区：
文献类型：
--
作者：
Wang, Wei;Sun, Xuemei;Yu, Yanlei
光致变形聚合物材料在人工肌肉、光致柔性驱动器、微光机械系统等领域有着广泛的应用前景，近年来得到了蓬勃发展。[1，2]其中，含有光致变色部分（例如偶氮苯）的交联液晶聚合物（CLCP）可以代表研究最多的系统之一，其具有由于偶氮苯中的反式-顺式光异构化引发的介晶分子取向的光诱导变化而引起的弯曲变形。[3-5]各种光驱动的软致动器，包括塑料马达，[6]尺蠖状步行器，[7]柔性微型机器人，[8]高频振荡器，[9]和人造纤毛[10]已经由CLCP制成。对于上述应用，关键是控制CLCP的弯曲方向，这取决于介晶的取向形式。例如，均匀取向的CLCP膜沿着介晶的取向方向朝向光源弯曲，[5]而垂直取向的膜远离光源弯曲。[11]为了在液晶（LC）系统中实现取向，通常对基板的表面进行改性以在制造期间为LC分子提供锚定作用。在许多方法中，优选的改性技术是机械摩擦。通常，首先通过沿沿着一个方向的机械摩擦产生具有平行凹槽的对准的聚酰亚胺（PI）层，然后使用凹槽来定向LC分子。[12]然而，仍然存在一些挑战，例如在制造过程中产生破碎碎片和结构损伤以及在使用过程中在表面上积累静电电荷，这在很大程度上限制了CLCP的应用。另一方面，碳纳米管（CNTs）由于其优异的机械和电学性能以及在可见/近红外（NIR）区域的良好吸收而受到广泛研究。据报道，CNT在温敏CLCP中的分散体产生了光可控网络，其能够在近红外光照射时收缩。[13]在这种情况下，CNT用作纳米级热源以吸收NIR光并进一步将其转化为热能，这引起CLCP从LC到各向同性的热相变，并具有热收缩。然而，对于这种间接光致动，灵敏度和稳定性都非常低。此外，由于碳纳米管的无规分散，CLCP中的液晶基元的取向仍然难以控制和改善，其他重要的性能，如机械强度也需要在此fabrication. There，我们报告了一种新的和通用的方法来制备光致变形CLCP/CNT纳米复合薄膜的发展，通过使用高度对齐的碳纳米管片。[14]作为示范，已仔细研究了含偶氮苯的光敏CLCP。结果发现，碳纳米管片的定向纳米结构可以有效地使CLCP介晶沿着碳纳米管的长度取向，而不使用任何其他取向层。所得的纳米复合膜通过用紫外光和可见光交替照射进行弯曲和伸直。此外，定向碳纳米管的引入显着提高了CLCP膜的机械强度，并提供导电性。两种单体A11 AB 6和A9 Bz 9以及交联剂C9 A的化学结构和性质示于方案1中。根据文献合成和纯化单体和交联剂。[15]合成的细节，1H...
Photodeformable polymeric materials have recently experienced vigorous development because of their potential applications in various fields, such as artificial muscle, photomobile soft actuator, and micro-optomechanical systems (MOMS).[1, 2] Among them, crosslinked liquid-crystalline polymers (CLCPs) containing photochromic moieties such as azobenzene may represent one of the most studied systems, with a bending deformation owing to a photoinduced change in the molecular orientation of mesogens triggered by the trans–cis photoisomerization in azobenzene.[3–5] Various lightdriven soft actuators including plastic motors,[6] inchwormlike walkers,[7] flexible microrobots,[8] high-frequency oscillators,[9] and artificial cilia [10] have been made from the CLCPs. For the above applications, it is critical to control the bending direction of the CLCPs which depends on the orientation format of the mesogens. For instance, a homogeneously oriented CLCP film bent towards the light source along the oriented direction of mesogens,[5] while a homeotropically oriented film bent away from the light source.[11] To achieve the orientation in a liquid-crystalline (LC) system, the surface of the substrate is usually modified to provide an anchoring action for LC molecules during fabrication. Of many methods, the preferred modification technique is mechanical rubbing. Typically, an aligned polyimide (PI) layer with parallel grooves is firstly generated by mechanical rubbing along one direction, and the grooves are then used to orient the LC molecules.[12] However, there remain several challenges, such as the production of broken debris and structural damage during fabrication and the accumulation of electrostatic charge on the surface during use, which have largely limited the application of the CLCPs. On the other hand, carbon nanotubes (CNTs) have been widely investigated for their extraordinary mechanical and electrical properties as well as good absorption in the visible/near-infrared (NIR) region. It has been reported that the dispersion of CNTs in a thermoresponsive CLCP created a light-controllable network, which enabled a contraction upon irradiation by NIR light.[13] In this case, the CNT functions as a nanoscale heat source to absorb the NIR light and further convert it to thermal energy, which induces a thermal phase transition of the CLCP from LC to isotropy with a thermal contraction. However, both sensitivity and stability are very low for such an indirect photoactuation. In addition, it remains difficult to control and improve the orientation of mesogens in the CLCP due to the random dispersion of CNTs, and the other important properties such as mechanical strength also need to be improved in this fabrication.Herein, we report the development of a new and general method to prepare photodeformable CLCP/CNT nanocomposite films by using highly aligned CNT sheets.[14] A photosensitive CLCP containing azobenzene has been carefully investigated as a demonstration. It was found that the aligned nanostructure of the CNT sheet could effectively orient the CLCP mesogens along the length of the CNTs without using any other aligning layer. The resulting nanocomposite film underwent bending and unbending by alternate irradiation with UV and visible light. Furthermore, the introduction of aligned CNTs remarkably increased the mechanical strength and provided electrical conductivity for the CLCP film. The chemical structures and properties of two monomers, A11AB6 and A9Bz9, and the crosslinker C9A, are shown in Scheme 1. The monomers and crosslinker were synthesized and purified according to the literature.[15] The synthetic details, 1H …