Orientation Approach to Directional Photodeformations in Glassy Side-Chain Azopolymers.
Orientation Approach to Directional Photodeformations in Glassy Side-Chain Azopolymers.
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DOI：
10.1021/acs.jpcb.9b00614
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发表时间：
2019-03
期刊：
影响因子：
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通讯作者：
Bharti Yadav;J. Domurath;Kwangjin Kim;Seungwoo Lee;M. Saphiannikova
中科院分区：
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作者：
Bharti Yadav;J. Domurath;Kwangjin Kim;Seungwoo Lee;M. Saphiannikova
为了使基于聚合物的材料具有光敏性，通常通过包含偶氮苯（偶氮）发色团来对其进行改性。它们与光的相互作用导致吸收的能量转化为机械功。波长约500 nm诱导环状反式-顺式异构化，这导致反式异构体垂直于光偏振的优选取向。这导致偶氮所连接的聚合物主链的重新取向和指示宏观变形方向的光诱导应力的出现。定向光致形变可以用取向方法来解释，其中偶氮分子的重取向可以用有效取向势来描述。在这里，我们展示了如何计算聚合物主链的时间依赖性取向状态和光致应力张量。对于侧链偶氮聚合物，在光偏振方向上的拉伸应力的预测。在有限元软件ANSYS的粘塑性材料模型中实现应力，我们表明方形偶氮聚合物柱沿着线偏振光的电场矢量伸长，并且沿着圆偏振光的传播方向收缩。粘塑性材料模拟的结果与微尺度方形柱和圆柱形柱的光致整形实验结果相一致。因此，定向方法对于均匀照明工作得相当好。我们将讨论如何使用这种方法来描述复杂的光干涉图案引起的表面变形。
To make a polymer-based material photosensitive, it is usually modified by inclusion of azobenzene (azo) chromophores. Their interaction with the light leads to conversion of absorbed energy into mechanical work. The wavelengths ∼500 nm induce cyclic trans-cis isomerization, which results in preferred orientation of the trans-isomers perpendicular to light polarization. This causes reorientation of the polymer backbones to which the azos are attached and appearance of the light-induced stress that dictates a direction of the macroscopic deformation. The directional photodeformations can be explained by an orientation approach, in which the reorientation of azos is described by the effective orientation potential. Here, we show how to calculate the time-dependent orientation state of the polymer backbones and the light-induced stress tensor. For side-chain azopolymers, a tensile stress in the direction of light polarization is predicted. Implementing the stress in a viscoplastic material model of the finite element software ANSYS, we show that a square azopolymer post elongates along the electric field vector for the linearly polarized light and contracts along the propagation direction for the circularly polarized light. These results of viscoplastic material modeling are in accordance with the experiments on light-induced reshaping of microscaled square and cylinder posts. Hence, the orientation approach works rather well for homogeneous illumination. We discuss how this approach can be used to describe surface deformations induced by complex light interference patterns.