支化聚电解质刷子对外界刺激响应的分子模拟研究

Compared with ordinary linear polymer brushes, branched polymer brushes possess some unique properties and hold great potential for technical applications. The effects of the topological architecture of branched polymer brushes, dendritic polymer brushes in particular, on the polymer chain conformations, monomer density, the scaling law of brush height, etc, have also stimulated intense theoretical and simulational research interest. This project intends to conduct Langevin molecular dynamics and off-lattice Monte Carlo simulations of the conformational behaviors of strong polyacid/base and weak polyacid/base branched brushes and their response to external stimuli (electric field, added monovalent and multivalent salt ions, solution pH, etc.). In this study, the influence of the topological structure of branched polymer brushes, the elastic effect of polymer chains, electrostatic interaction, the entropic effect of counterions, solution pH, external electric fields and added multivalent salt ions on the chain conformations, the distributions of monomers and counterions, the scaling law of brush heights will be quantitatively examined, with the aim of elucidating the molecular mechanism that governs how the topological structure of branched polymer brushes and external stimuli regulate the stratification of grafted branched polymer chains and the acid-base ionization equilibrium in weak polyacid/base branched polymer brushes, thus laying a solid theoretical foundation for the experimental design and fabrication of excellent stimuli-responsive branched polyelectrolyte brushes.

支化高分子刷子具有不同于普通线型高分子刷子的一些独特的性质和潜在应用前景, 支化高分子刷子尤其是树枝状刷子的拓扑结构对高分子链构象、单体浓度、刷子高度标度率等的影响也引起了高分子物理理论和模拟领域的极大兴趣。本项目拟运用Langevin分子动力学和无格点蒙特卡罗方法模拟研究强酸/强碱型和弱酸/弱碱型支化聚电解质刷子的构象行为及其对外界刺激(电场、外加盐离子、溶液pH值等)的响应，定量分析支化链的拓扑结构、高分子链弹性、静电作用、反离子熵效应、溶液pH值、外加电场和外加高价盐离子这几大因素对高分子链构象、单体和反离子分布、刷子高度标度率等的影响规律，阐明支化链的拓扑结构和外界刺激对刷子中接枝高分子链分层和弱酸/弱碱型支化高分子链酸-碱电离平衡的作用机理，为实验设计和制备优良的对外界刺激响应的支化聚电解质刷子奠定较为坚实的理论基础。

我们按照自然科学基金任务书的要求,运用朗之万分子动力学方法模拟和自洽平均场解析理论研究支化聚电解质刷子的构象行为和其对外界刺激的响应。我们对强酸/强碱型支化高分子刷子对外加电场、单价和高价盐离子的响应,以及线性/支化混合聚电解质刷对外加电场、盐离子、溶剂性质等的响应进行了系统的研究。定量分析了高分子链弹性、静电相互作用、反离子熵效应、外加电场以及高电价态盐反离子的桥联效应等因素对高分子链构象、单体和反离子分布、电极板附近电荷平衡、刷子高度标度率等的影响并揭示其影响规律，阐明了外界刺激对支化聚电解质刷内部分层现象的作用机理,并对外加高电价态盐反离子导致支化聚电解质刷子塌缩的分子内部的支化链段内/链段间以及分子之间的桥联作用、静电强相关联效应进行了较为深入的探讨。本项目比较好的完成了基金项目的任务目标, 为实验设计和制备优良的对外界刺激响应的支化聚电解质刷子奠定较为坚实的理论基础。本项目研究不足之处是未能解决弱酸/弱碱型支化高分子刷子Monte-Carlo模拟方法的建立和程序验证中出现的问题。