Toshchevikov V, Saphiannikova M, Heinrich G
Leibniz Institute of Polymer Research Dresden, 01069 Dresden, Germany.
J Phys Chem B. 2009 Apr 16;113(15):5032-45. doi: 10.1021/jp8078265.
We propose a microscopic theory of light-induced deformation of side-chain azobenzene polymers taking into account the internal structure of polymer chains. Our theory is based on the fact that interaction of chromophores with the polarized light leads to the orientation anisotropy of azobenzene macromolecules which is accompanied by the appearance of mechanical stress. It is the first microscopic theory which provides the value of the light-induced stress larger than the yield stress. This result explains a possibility for the inscription of surface relief gratings in glassy side-chain azobenzene polymers. For some chemical architectures, elongation of a sample demonstrates a nonmonotonic behavior with the light intensity and can change its sign (a stretched sample starts to be uniaxially compressed), in agreement with experiments. Using a viscoplastic approach, we show that the irreversible strain of a sample, which remains after the light is switched off, decreases with increasing temperature and can disappear at certain temperature below the glass transition temperature. This theoretical prediction is also confirmed by recent experiments.
我们提出了一种考虑聚合物链内部结构的侧链偶氮苯聚合物光致变形的微观理论。我们的理论基于这样一个事实，即发色团与偏振光的相互作用导致偶氮苯大分子的取向各向异性，同时伴随着机械应力的出现。这是第一个能给出大于屈服应力的光致应力值的微观理论。这一结果解释了在玻璃态侧链偶氮苯聚合物中写入表面起伏光栅的可能性。对于某些化学结构，样品的伸长表现出随光强的非单调行为，并且可以改变其符号（拉伸的样品开始被单轴压缩），这与实验结果一致。使用粘塑性方法，我们表明，在光关闭后样品剩余的不可逆应变随温度升高而减小，并且在低于玻璃化转变温度的特定温度下可能消失。这一理论预测也得到了最近实验的证实。
