Liquid crystal anchoring transformations induced by phase transitions of a photoisomerizable surfactant at the nematic/aqueous interface
Liquid crystal anchoring transformations induced by phase transitions of a photoisomerizable surfactant at the nematic/aqueous interface
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DOI：
10.1039/b821980j
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发表时间：
2009-01-01
期刊：
影响因子：
3.4
通讯作者：
Schwartz, Daniel K.
中科院分区：
文献类型：
--
作者：
Price, Andrew D.;Ignes-Mullol, Jordi;Schwartz, Daniel K.
将含有偶氮苯单元的光致异构脂肪酸溶解于水溶性液晶（LC）中，并吸附在LC/水界面上，影响LC材料的锚定。在将系统暴露于不同的照射波长时观察到LC相的重新取向。在各种热力学和光照条件下，均观察到各向同性，倾斜和平面锚定。显示不同锚定的区域之间的横向共存经常被观察到，因为是动态的和可逆的各种状态之间的转换。这些观察结果表明，吸附单层的偶氮苯-脂肪酸（可能在溶液中与相同的表面活性剂平衡）显示丰富的二元相图，其中的顺式和反式异构体的相对分数由与照明波长相关的光稳态确定。这些相图的形态已被确定为三个变量的函数-体积浓度，温度，和组合物（顺反比）的溶解的表面活性剂和六个不同的界面相被确定，包括五个凝聚相和稀释的界面气相。该相图不同于在空气/水界面处的相同两亲物的朗缪尔单层的行为，其仅表现出两个凝聚相。
A photoisomerizable fatty acid (containing an azobenzene unit) was dissolved in a nematic liquid crystal (LC), and adsorbed at the LC/water interface, influencing the anchoring of the LC material. Reorientation of the LC phase was observed upon exposure of the system to different irradiation wavelengths. Homeotropic, tilted, and planar anchoring were all observed under various thermodynamic and illumination conditions. Lateral coexistence between regions displaying different anchoring was often observed, as were dynamic and reversible transitions between the various states. These observations suggest that adsorbed monolayers of the azobenzene-fatty acid (probably in equilibrium with the same surfactant in solution) display a rich binary phase diagram, where the relative fractions of cis and trans isomers are determined by the photostationary state associated with the illumination wavelength. The morphology of these phase diagrams has been determined as a function of three variables-bulk concentration, temperature, and composition (cis-trans ratio) of the dissolved surfactant-and six distinct interfacial phases were identified, including five condensed phases and a dilute interfacial vapor phase. This phase diagram is distinct from the behavior of Langmuir monolayers of the same amphiphile at the air/water interface, which exhibits only two condensed phases.