Modeling of Stripe Patterns in Photosensitive Azopolymers
Modeling of Stripe Patterns in Photosensitive Azopolymers
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DOI：
10.3390/polym12040735
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发表时间：
2020-03
期刊：
影响因子：
5
通讯作者：
Bharti Yadav;J. Domurath;M. Saphiannikova
中科院分区：
文献类型：
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作者：
Bharti Yadav;J. Domurath;M. Saphiannikova
放置在界面上的含偶氮苯材料在受到外部光源照射时会表现出非凡的现象。在这里，我们模拟偶氮聚合物薄膜中一维高斯光场引起的表面变化。这种场可以在快速移动的薄膜中产生，并用强聚焦激光束照射或通过柱面透镜照射样品。为了解释条纹图案的出现，我们首先计算薄膜内部一维高斯场引起的不平衡机械应力。根据我们的取向方法，光引起的应力源自偶氮苯的重新取向，这导致刚性主链片段沿着光偏振方向取向。对于垂直和平行于移动方向的光偏振，所产生的体积力具有不同的符号和幅度。因此，通过拉伸力产生凹槽并且通过压缩力产生细长突出部。根据实验观察，在有限元软件中实施粘塑性模型可以预测沿移动方向偏振的光的影响要弱得多。在这种情况下，光诱导应力分布的最大值变得非常接近屈服应力，这导致玻璃状偶氮聚合物的表面变形更小。
Placed at interfaces, azobenzene-containing materials show extraordinary phenomena when subjected to external light sources. Here we model the surface changes induced by one-dimensional Gaussian light fields in thin azopolymer films. Such fields can be produced in a quickly moving film irradiated with a strongly focused laser beam or illuminating the sample through a cylindrical lens. To explain the appearance of stripe patterns, we first calculate the unbalanced mechanical stresses induced by one-dimensional Gaussian fields in the interior of the film. In accordance with our orientation approach, the light-induced stress originates from the reorientation of azobenzenes that causes orientation of rigid backbone segments along the light polarization. The resulting volume forces have different signs and amplitude for light polarization directed perpendicular and parallel to the moving direction. Accordingly, the grooves are produced by the stretching forces and elongated protrusions by the compressive forces. Implementation into a viscoplastic model in a finite element software predicts a considerably weaker effect for the light polarized along the moving direction, in accordance with the experimental observations. The maximum value in the distribution of light-induced stresses becomes in this case very close to the yield stress which results in smaller surface deformations of the glassy azopolymer.