扭曲弯曲的液晶的高对比度和快速光圈开关
1RIKEN Center for Emergent Matter Science (CEMS), 2Institute for Solid State Physics and Optics, Wigner Research Center for Physics,Hungarian Academy of Sciences, 3Department of Chemistry, School of Natural and Computing Sciences,University of Aberdeen, 4Chemical Physics Interdisciplinary Program and Liquid Crystal Institute,Kent State University
Summary
该协议演示了光热材料的制备，该材料通过增加温度来显示固体相、各种液晶相和各向异性液相。这里介绍了测量材料的结构-粘弹性关系的方法。
Abstract
响应特定刺激的智能粘弹性材料是未来技术中最具吸引力的材料类别之一，例如按需可切换粘附技术、执行器、分子离合器和纳米/微观质量转运 蛋白。最近发现，通过特殊的固液过渡，流变特性可以表现出显著的变化，从而提供合适的智能粘弹性材料。然而，使用这种特性设计材料是复杂的，向前和向后切换时间通常很长。因此，探索新的工作机制，实现固体-液体转换，缩短开关时间，增强开关过程中的流变特性对比，具有十分重要的意义。在这里，观察到光诱导的液晶相变，其特点是偏振光显微镜（POM）、光热测量、光差扫描热度（光DSC）和X射线衍射（XRD）。光诱导的液晶相变具有以下关键特征：（1）前后反应的液晶相快速切换，以及（2）粘弹性的高对比度。在表征中，POM在提供有关LC分子方向的空间分布信息、确定材料中出现的液晶相的类型以及研究LC的方向方面具有优势。允许在光刺激下测量材料的流变特性，并可以揭示材料的光河开关特性。Photo-DSC是一种在黑暗和光照射下研究材料热力学信息的技术。最后，XRD允许研究材料的微观结构。本文的目的是清楚地介绍如何准备和测量光河学材料的讨论性质。
Introduction
能够改变其粘弹性特性以响应环境变化的智能机械材料引起了研究人员的极大兴趣。可切换性被认为是最重要的物质因素，它为生物体中的重复机械反应提供了鲁棒性。迄今为止，利用软质（即光反应水凝胶1、2、3、聚合物4、5、5、）设计了具有多功能功能的人工可切换材料。6，7，8，9，10，11，液晶 [LC]9，10，11， 12，13，14，15，16，17，pH响应型云母18，19，20 ，21，22和表面活性剂23。然而，这些材料存在以下不止一个问题：缺乏可逆性、粘弹性开关对比度低、适应性低和开关速度慢。在传统材料中，粘弹性的开关对比度与开关速度之间存在权衡;因此，设计涵盖所有这些高标准的材料具有挑战性。为了实现具有上述无所不能的材料，选择或设计具有高流动性（粘度）和刚度（弹性特性）的突发性分子至关重要。
液晶是理想的系统，具有潜在的大量液晶和固体相，可以通过分子设计进行调谐。这允许在特定的LC相级的不同长度尺度上进行自组装结构。例如，高对称内形 LC （NLC） 由于其短距离空间顺序而表现出低粘度和弹性，而低对称柱或薄色 LC 则由于一维和二维远程，表现出高粘度和弹性周期性。如果LC材料可以在两相之间切换，其粘弹性性能差异较大，则可实现高性能的粘弹性智能材料。据报有9、10、11、12、13、14、15的例子。
本文演示了光热LC材料的制备，其相序为各向异性（I）-核质（N）-扭弯（TB）24-晶体（在加热时，反之亦然），其表现出快速和可逆粘弹性开关响应光。这里介绍了测量粘弹性的方法，并说明了微观结构与粘弹性的关系。详细信息在代表性结果和讨论部分中介绍。
Protocol
1. 制备摩擦表面，以平面方式对齐LC分子 准备干净的玻璃基板。 使用金刚石玻璃切割器（材料表）将玻璃基板切割成小方形，平均尺寸为1厘米x1厘米。在碱性洗涤剂（材料表）中，以38 kHz或42 kHz的声波将其洗涤。洗涤剂：水体积比为1：3），用蒸馏水反复冲洗（通常，每次冲洗超过10倍，声波5分钟）。 使基材接受紫外线臭氧（UV-O3）清洁剂?…
Representative Results
POM 图像、光测量数据、光 DSC 数据和 XRD 强度曲线是在温度变化和照射紫外线时在黑暗中收集的。图 1a，b表示 CB6OABOBu 的结构，其相序和可能的一致性由建模程序中 MM2 力场优化（例如，ChemBio3D）。 当CB6OABOBu处于跨态时，会出现两种能量可感的构象状态，而扭曲的构象是促进结核病阶段形成的最稳定的构象。当 CB6OABOBu 在暴露于紫外线时对顺…
Discussion
如图1所示，CB6OABOBu是一种光响应材料，冷却时具有I、N、TB和哭相序列。由于这些相的局部顺序差异很大，风变特性的光驱动切换预计将表现出良好的粘弹性对比度。为了定量地调查这一点，进行了光变学测量。
首先，我们考虑在黑暗中测量的流变数据（图2a，红色开放圆圈）。在I-N相变时，有效粘度（αeff?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
这项工作得到了HAS-JSPS双边联合研究项目的支持。NKFIH PD 121019 和 FK 125134 的赠款提供财政支持。
Materials
| 21-401-10 | AS ONE | Microspatula | |
| AL1254 | JSR | Planar alignment agent for liquid crystals | |
| BX53P | Olympus | Polarising microscope with transmission/epi-illumination units | |
| Discovery DSC 25P | TI instruments | Photo-DSC equipment | |
| Glass cutter PRO-1A | Sankyo | A diamond-based glass cutter | |
| HS82 | Mettler Toledo | hot stage | |
| MCR502 | Anton Paar | A commercial rheometer | |
| MRJ-100S | EHC | Rubbing machine | |
| Norland Optical Adhesive 65, 81 | Norland Products | Photoreactive adhesions | |
| OmniCure S2000 | Excelitas Technologies | A commericial high-pressure mercury vapor short arc lamp. Maximum 70 mW/cm^2. | |
| PILATUS 6M | Dectris | Hybrid photon counting detector for X-ray diffraction dectection | |
| S1126 | Matsunami Glass | Glass substrate | |
| SC-158H | EHC | Spin coater | |
| SCAT-20X | DKS | Alkaline detergent | |
| SLUV-4 | AS ONE | Low-pressure mercury vapor short arc lamp | |
| UV-208 | Technovision | Ultraviolet-ozone (UV-O3) cleaner |
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Cite This Article
Aya, S., Salamon, P., Paterson, D. A., Storey, J. M. D., Imrie, C. T., Araoka, F., Jákli, A., Buka, Á. High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal. J. Vis. Exp. (152), e60433, doi:10.3791/60433 (2019).