Oyerokun Folusho T, Schweizer Kenneth S
Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
J Chem Phys. 2005 Dec 8;123(22):224901. doi: 10.1063/1.2135776.
A mode coupling theory for the ideal glass transition temperature, or crossover temperature to highly activated dynamics in the deeply supercooled regime, T(c), has been developed for anisotropic polymer liquids. A generalization of a simplified mode coupling approach at the coarse-grained segment level is employed which utilizes structural and thermodynamic information from the anisotropic polymer reference interaction site model theory. Conformational alignment or/and coil deformation modifies equilibrium properties and constraining interchain forces thereby inducing anisotropic segmental dynamics. For liquid-crystalline polymers a small suppression of T(c) with increasing nematic or discotic orientational order is predicted. The underlying mechanism is reduction of the degree of coil interpenetration and intermolecular repulsive contacts due to segmental alignment. For rubber networks chain deformation results in an enhanced bulk modulus and a modest elevation of T(c) is predicted. The theory can also be qualitatively applied to systems that undergo nonuniversal local deformation and alignment, such as polymer thin films and grafted brush layers, and large elevations or depressions of T(c) are possible. Extension to treat directionally dependent collective barrier formation and activated hopping is possible.
针对各向异性聚合物液体，已开发出一种用于理想玻璃化转变温度或深度过冷状态下向高活化动力学转变温度(T(c))的模式耦合理论。采用了粗粒化链段水平上简化模式耦合方法的推广形式，该方法利用了来自各向异性聚合物参考相互作用位点模型理论的结构和热力学信息。构象排列或/和线团变形会改变平衡性质并限制链间作用力，从而引发各向异性链段动力学。对于液晶聚合物，预计随着向列相或盘状取向序增加，(T(c))会有小幅降低。其潜在机制是由于链段排列导致线团相互贯穿程度和分子间排斥接触减少。对于橡胶网络，链变形会导致体积模量增加，并预计(T(c))会有适度升高。该理论还可定性应用于经历非普适局部变形和排列的体系，如聚合物薄膜和接枝刷层，(T(c))可能会有大幅升高或降低。扩展该理论以处理方向依赖性集体势垒形成和活化跳跃是可行的。
