受限条件下半刚性高分子体系的相行为的理论研究

The phase behaviors of semiflexible chains in confined system is a basic topic both in natural and artificial polymeric system. Many problems in biology and material science, such as the structure of virus, packing of polymer in metal-organic frameworks and condensed structure of polymer in optoelectronic device can be studied by modeling them as confined semiflexible chain systems. The introduction of confinement leads to the symmetry broken both in orientational and translational order by forming complex structures in three-dimensional space. These structures affect the dynamics of phase transition and the response to the external stimulation of confined system, which determines their physical properties. In this project, based on the newly developed single chain mean-field theory for semiflexible chain with high efficiency and precision, the phase behaviors of semiflexible chain confined in both isotropic and anisotropic system will be concentrated on. A multi-scale investigation will be performed both in the scale of radius of gyration and persistence length comprehensively. By searching all possible order structures and determining their stability, a phase diagram will be obtained which serves as the theoretical support for both understanding the structure formation and the realization of the physiological functions in biological polymer confined system, and the synthesis and the performance optimization of artificial polymer devices.

受限半刚性高分子的相行为是天然和人工高分子体系中被人们普遍关心的基本问题。生物学中病毒的结构、材料科学上填充在金属-有机框架中的高分子的堆积结构以及光电子器件中高分子的凝聚态结构都可以被模型化为受限的半刚性高分子体系。受限条件的引入将导致体系取向序和平移不变性的破缺，进而在三维空间中形成复杂的结构。这些结构影响着受限体系的相转变动力学及其对外界的响应，是实际受限高分子体系中物理性能实现的基础。本项目基于本课题组新发展的高效、高精度的半刚性链的单链平均场理论方法，围绕受限半刚性高分子体系的相行为这一核心内容，分别在各向同性和各向异性的受限条件下，讨论高分子在回转半径和持续长度两个尺度上的受限效应；通过寻找可能的有序结构，判断各结构的稳定性，来绘制出受限在硬壳中半刚性高分子体系的相图；为理解生物高分子受限体系中结构的形成与生理功能的实现以及人工高分子受限器件的制备与性能的调控提供理论支持。

受限体系中高分子的构象统计和所形成的有序结构是高分子物理关心的基本问题。本项目采用蠕虫链模型的平均场理论来研究强受限效应，即体系特征尺度接近高分子持久长度的体系中的新效应。传统基于扩散方程数值求解的自洽场理论难以处理本项目关心的受限和有曲率表面体系的问题。我们结合平均场理论和分子模拟技术开发了蠕虫链模型的单链平均场理论。其基本思想是采用路径积分求解物理量的系综平均值方法来代替自洽场理论中先数值求解传播子再计算系综平均的方法。由于这一理论具有适用性强、通讯损耗低、并行化效率高等优势，我们结合超性能计算平台（天河II号）的使用深入探索了该理论的高效数值解决方案，拓展了该理论的适用性和大规模计算能力。应用这一理论，开展了系列的受限体系中半刚性高分子的研究，包括平板受限下具有液晶序的高分子刷的力学响应，受限于曲面间反应性高分子刷的反应概率，光响应性高分子刷，以及高分子结晶体系的研究。理论工作的实践表明相比高斯链模型所描述的柔性高分子体系，具有半刚性的高分子链在受限环境中以及有曲率表面体系中展示出更加丰富的结构和独特的响应性质。本项目的顺利完成为半刚性高分子体系的研究提供有力的平均场理论工具，并为半刚性高分子的响应行为的深入研究奠定了基础。