Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, 01069 Dresden, Germany.
J Chem Phys. 2012 Jul 14;137(2):024903. doi: 10.1063/1.4731663.
Azobenzene elastomers 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 theoretical approaches to accurately predict the quantitative response of these materials based on their microscopic structure. Recently, we proposed a theory of light-induced deformation of azobenzene elastomers using a simple regular cubic network model [V. Toshchevikov, M. Saphiannikova, and G. Heinrich, J. Phys. Chem. B 116, 913 (2012)]. In the present study, we extend the previous theory using more realistic network models which take into account the random orientation of end-to-end vectors of network strands as well as the molecular weight distribution of the strands. Interaction of the chromophores with the linearly polarized light is described by an effective orientation potential which orients the chromophores perpendicular to the polarization direction. We show that both monodisperse and polydisperse azobenzene elastomers can demonstrate either a uniaxial expansion or contraction along the polarization direction. The sign of deformation (expansion/contraction) depends on the orientation distribution of chromophores with respect to the main chains which is defined by the chemical structure and by the lengths of spacers. The degree of cross-linking and the polydispersity of network strands do not affect the sign of deformation but influence the magnitude of light-induced deformation. We demonstrate that photo-mechanical properties of mono- and poly-disperse azobenzene elastomers with random spatial distribution of network strands can be described in a very good approximation by a regular cubic network model with an appropriately chosen length of the strands.
偶氮苯弹性体在过去十年中被广泛探索作为光变形智能材料，能够将光能转化为机械应力。目前，非常需要理论方法来准确预测这些材料的定量响应，基于它们的微观结构。最近，我们提出了一种使用简单正则立方网络模型预测偶氮苯弹性体光致变形的理论[V. Toshchevikov、M. Saphiannikova 和 G. Heinrich，J. Phys. Chem. B 116, 913（2012）]。在本研究中，我们使用更现实的网络模型扩展了以前的理论，该模型考虑了网络链末端矢量的随机取向以及链的分子量分布。发色团与线性偏振光的相互作用由有效取向势描述，该势将发色团取向垂直于偏振方向。我们表明，单分散和多分散偶氮苯弹性体都可以沿偏振方向表现出单轴膨胀或收缩。变形的符号（膨胀/收缩）取决于发色团相对于主链的取向分布，该分布由化学结构和间隔物的长度定义。交联度和网络链的多分散性不会影响变形的符号，但会影响光致变形的程度。我们证明，具有网络链随机空间分布的单分散和多分散偶氮苯弹性体的光机械性能可以通过适当选择链长的正则立方网络模型很好地近似描述。
