Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan, ROC.
J Phys Chem B. 2009 Dec 10;113(49):15937-48. doi: 10.1021/jp907338j.
Innovation in modern material science exploiting conducting conjugated polymers imperatively demands fundamental knowledge of single-chain conformations from solution to the quenching state. This urgent goal, however, poses a stringent challenge to existing simulation schemes, especially when the polymer of interest possesses simultaneously a high molecular weight and anisotropic local interaction forces, such as hydrogen-bond (HB) and pi-pi interactions. Considering a standard case with polyaniline emeraldine base (PANI-EB), widely used as the conducting layer in polymer-based optoelectronic devices, this paper introduces how the current difficulty may be circumvented by using a multiscale simulation scheme that takes advantage of a systematic mapping and back-mapping between atomistic molecular dynamics (AMD), coarse-grained molecular dynamics, and coarse-grained Langevin dynamics (CGLD). Whereas a self-consistent CGLD simulation greatly facilitates reaching representative long-chain conformations in specific solvents, the back-mapped AMD simulation permits scrutiny into the effects of localized HB and pi-pi interactions on quenched chain morphologies. The basic idea behind this multiphase simulation scheme for conducting conjugated polymers has been consolidated by the central observation for PANI-EB: whereas segmental van der Waals interactions dominate fundamental single-chain properties in solution (i.e., persistence length, solvent quality, and chain diffusivity), the anisotropic HB and pi-pi interactions accordingly "trap" the quenched chain to a morphology closely mimicking that in the prior solution state-the first microscopic evidence of the so-called "memory effect." Notably, the central features disclosed for PANI-EB as well as the multiscale simulation strategy proposed for tracking single-chain conformations from solution to the quenching state are asserted to hold for typical conducting conjugated polymers that possess, ubiquitously, a semiflexible backbone and localized interaction forces.
现代材料科学中的创新利用导电共轭聚合物迫切需要从溶液到猝灭状态的单链构象的基本知识。然而，这一紧迫的目标对现有的模拟方案提出了严格的挑战，特别是当所关注的聚合物同时具有高分子量和各向异性的局部相互作用力时，如氢键 (HB) 和 π-π 相互作用。考虑到一个标准的例子，即用聚亚胺 Emeraldine 碱 (PANI-EB)，它广泛用作聚合物基光电设备中的导电层，本文介绍了如何通过使用多尺度模拟方案来克服当前的困难，该方案利用原子分子动力学 (AMD)、粗粒化分子动力学和粗粒化朗之万动力学 (CGLD) 之间的系统映射和反向映射。虽然自洽的 CGLD 模拟极大地促进了在特定溶剂中达到代表性长链构象，但反向映射的 AMD 模拟允许研究局部 HB 和 π-π 相互作用对猝灭链形态的影响。对于导电共轭聚合物的这种多相模拟方案的基本思想是通过对 PANI-EB 的中心观察得到的：尽管段间范德华相互作用在溶液中主导基本的单链性质（即，持久性长度、溶剂质量和链扩散系数），各向异性的 HB 和 π-π 相互作用相应地“捕获”猝灭链，使其形态紧密模仿先前的溶液状态——这是所谓的“记忆效应”的第一个微观证据。值得注意的是，为 PANI-EB 揭示的中心特征以及为从溶液到猝灭状态跟踪单链构象而提出的多尺度模拟策略被断言适用于普遍具有半柔性骨架和局部相互作用力的典型导电共轭聚合物。
