不同基体刚性偶氮化合物光致光学各向异性及其唯象模拟

Photoinduced Anisotropy of Azo Polymer with Different Matrices Rigidity and Their Phenomenological Simulation

在不同刚性的聚合物基体聚甲基丙烯酸甲酯(PMMA)、聚乙烯咔唑(PVK)和聚苯乙烯(PS)薄膜基体中掺入相同质量分数(均为0.003)的分散红13(DR13)偶氮染料。以线偏振连续Ar+激光(514 nm)作为控制光,连续He-Ne激光(632.8 nm)作为信号光考察了具有相同厚度的三种样品在相同控制光功率(15 mW)下的光致双折射效应。实验发现刚性较大的聚乙烯咔唑基体样品的双折射效应最小,刚性最小的聚苯乙烯基体样品的双折射效应最大。在偶氮生色团光致异构的四能级模型基础上,建立一新的唯象的模型。在模型中引入描述聚合物基体刚性的参量s,通过数值计算描述了不同基体刚性参量s对偶氮生色团光致异构取向的影响。计算结果表明,基体的刚性越大,样品的光致双折射效应越小,定性地解释了实验现象。

Three kinds of polymeric films with different rigidity, poly （methyl methacrylate） （PMMA）, poly （N-vinylcarbazole） （PVK） and polystyrene （PS）, which were doped with same concentration （mass fraction 0. 003） of azo-dye 4′-[[2-（acryloyloxy）ethyl]ethylamino]-2-chloro-4-nitroazobenzene （disperse red 13, DR13）, were prepared. The photoinduced birefringence effect of these three kinds of samples were studied by using a linearly polarized control beam from an Ar^＋ laser （514 nm） and a linearly polarized probe beam from a He-Ne laser （632.8 nm）. It was found that under the same control beam power （15 mW） and with the same sample＇s thickness, the PVK with large matrix rigidity showed small birefringence effect while polystyrene with small matrix rigidity showed large birefringence effect. Based on the four-energy-level model of photoisomerization of azo chromophores, a phenomenological model, in which a parameter s was introduced to describe the rigidity of polymer matrices, was presented to simulate the photoisomerization and orientation of the azo chromophores in polymeric matrices with different rigidity. The influence of the matrix rigidity parameter s on the photoinduced anisotropy of the azo-dye containing samples was investigated by numerical calculation. The computed results showed that large rigidity samples present small birefringence effect and the experimental results could be explained qualitatively by the theoretical simulation results.