Title: Simultaneous Analysis of Optical and Mechanical Properties of Cross-linked Azobenzene-containing Liquid-crystalline Polymer Films

Author: Aki Shimamura, Arri Priimagi, Jun-ichi Mamiya, Tomiki Ikeda*, Yanlei Yu, Christopher J. Barrett, Atsushi Shishido*

Journal: ACS Appl. Mater. Interfaces, 2011, 3(11), 4190-4196

Abstract:

The photomechanical behavior of cross-linked azobenzene-containing liquid-crystalline polymer films was investigated by means of simultaneous measurement of their optical and mechanical properties. The connection between photoisomerization of the azobenzene moieties, photoinduced change in molecular alignment, photoinduced stress generation, and macroscopic bending was analyzed. Upon UV irradiation, the films exhibited bending due to gradient in cis-azobenzene content, and subsequent unbending when cis-azobenzene content became uniform throughout the film. The maximum photoinduced stress was generated in the same time scale as the time required to reach photostationary state in the cis-azobenzene concentration. The maximum values of photogenerated stress strongly depended on the crosslinker concentration, even if the azobenzene concentration and the cis-azobenzene content in the photostationary state were similar for all the polymer films. The stress is connected to the initial Young’s modulus and also to the photoinduced change in birefringence of the polymer films. In addition, a significant photoinduced decrease in Young’s modulus was for the first time observed in cross-linked azobenzene-containing liquid-crystalline polymers, which is likely to be an important factor in dictating their photomechanical behavior.

论文链接：https://pubs.acs.org/doi/abs/10.1021/am200621j

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本文研究了含偶氮苯的交联液晶聚合物的光致异构化、光诱导的分子排列变化、光诱导应力和宏观弯曲之间的相互关系。我们发现，顺式偶氮苯的产生会引起薄膜的双折射变化，而双折射变化与薄膜内部应力的产生直接相关。此外，通过研究不同交联程度的样品，我们指出，低的杨氏模量有利于材料的宏观变形，而高的杨氏模量促进材料体系产生高的光致应力。最后，观察到在紫外照射下，含偶氮苯的交联液晶聚合物的杨氏模量降低，我们认为这与均匀排列的交联液晶聚合物产生“缺陷”(顺式异构体)有关。