Theory of photo-mechanical properties of azobenzene polymers: light-induced deformation dynamics

在过去的十年中，偶氮苯聚合物作为一种能够将光能转化为机械应力的光变形智能材料得到了广泛的研究。目前，迫切需要基于这些材料的微观结构对其动态响应进行定量预测。本项目的目的是为两类广泛使用的偶氮聚合物：玻璃聚合物和高弹性网络（弹性体）发展光诱导变形动力学理论。将考虑不同效应对光致变形动力学的影响：(i)导致光学各向异性和光致机械应力的光异构动力学，（ii）嵌入聚合物基质中的偶氮发色团的集体运动，以及（iii）分子间相互作用，例如玻璃聚合物中的短尺度相互作用和液晶偶氮聚合物中的长尺度定向相互作用。光致变形的时间依赖性将被计算为光强度、偶氮分子的聚合程度、交联程度、偶氮分子内发色团的取向分布、分子间相互作用的强度、偶氮发色团的物理特性（如它们的尺寸和吸收系数等）的函数。该项目建立的结构-性能关系对于定向开发用于各种纳米和微尺度应用的光可控高速器件的偶氮聚合物具有重要意义。

Azobenzene polymers (azo-polymers) have been extensively explored in the last decade as photo-deformable smart materials which are able to transform light energy into mechanical stress. Presently, there is a great need for quantitative prediction of the dynamic response of these materials based on their microscopic structure. The aim of this project is to develop a theory of the light-induced deformation dynamics for two widely used classes of azo-polymers: glassy polymers and highly elastic networks (elastomers). The influence of different effects on the dynamics of light-induced deformation will be taken into account: (i) photoisomerisation kinetics which results in the optical anisotropy and light-induced mechanical stress, (ii) collective motions of azo-chromophores embedded into a polymer matrix, and (iii) intermolecular interactions such as short-scale interactions in glassy polymers and long-scale orientational interactions in liquid crystalline azo-polymers. The time dependences of the light-induced deformation will be calculated as a function of the light intensity, the degree of polymerization of the azo-molecules, the degree of cross-linking, orientation distribution of chromophores inside azo-molecules, strengths of intermolecular interactions, physical characteristics of azo-chromophores such as their dimensions and absorption coefficient, etc. Structure-property relationships established during the project are of great importance for targeted development of azo-polymers to be used in light-controllable high-speed devices for various nano- and microscale applications.