半刚性高分子/纳米粒子复合体系相行为的自洽场理论研究

Polymer nanocomposites (PNCs) have attracted much interest because of their excellent physical and mechanical properties. However, the nanoscale particles typically aggregate or separate from the polymer matrix, which negates any benefits associated with the nanoscopic dimension. In practical applications, many polymer matrix of PNCs, such as polyimide, the copolyester, have a certain degree of chain rigidity, leading to a scientific challenge for theoretical investigation. In this project, in order to explore the self-assembled behavior and the physical mechanism of the hybrids, we will develop a mean field theory for mixtures of semiflexible polymers and nanoparticles. The method combines a self-consistent field theory (SCFT) based on wormlike chain model for semiflexible polymers and a density functional theory (DFT) for particles. In the wormlike chain model, the addition of the chain segment orientation makes it difficult to solve the diffusion equation of wormlike chain propagator. Thus, the applications of SCFT based on wormlike chain model have now been limited in the study of simple systems. With the help of the accurate and efficient pseudo-spectral numerical algorithm, we will extend this method to more complex systems and systematically investigate the influence of nanoparticles on thermodynamics of binary polymer mixture and the phase structures and phase behavior of the diblock copolymer-nanoparticle composites, amphiphilic nanoparticle-semiflexible chain macromolecules, and semiflexible polymer brushes. Furthermore, we will explore the relationship between the mesophases of polymer-nanoparticle composites and the mechanical and rheological properties of the composite materials. This study will provide a theoretical guide for the preparation and application of polymer nanocomposites, such as polyimide/nanoparticles composite, high-performance engineering plastics.

聚合物纳米复合材料由于其具有优异的物理机械性能,引起科学界的广泛关注。然而纳米粒子容易团聚,或从聚合物中分离出来，抑制了材料与纳米级尺寸相关的优异性能。实际复合材料中的高分子基体很多存在一定程度的链刚性，如聚酰亚胺、共聚酯等，这给理论研究带来很大挑战。本项目拟采用基于蠕虫状链模型的半刚性高分子自洽平均场理论，结合纳米粒子硬球相互作用的密度泛函理论，发展适合于描述具有链刚性高分子基纳米复合体系相行为的场论方法。由于刚性链段取向参数的存在加大了扩散方程的数值求解难度，大多应用限于比较简单和基本的半刚性高分子体系。因此，借助精确、高效的准谱数值算法将其应用扩展到更为复杂的体系，以期成功预测纳米粒子与半刚性高分子共混及接枝情况下的相结构和相行为；探索复合体系相结构与材料力学、流变性能之间的关系。这一方法将为研究聚合物纳米复合体系如聚酰亚胺纳米复合材料、高性能工程塑料的制备和应用提供理论指导。

本项目主要采用自洽场理论方法研究含有链刚性嵌段共聚物的相行为及其柔性-半刚性嵌段共聚物/纳米粒子复合体系的相行为，并与实验相结合重点开展新型高性能材料聚酰亚胺分子设计和性能预测研究。. 采用基于蠕虫状链模型和高斯链模型的自洽场理论方法研究了对称柔性-半刚性-柔性三嵌段共聚物自组装行为。在设定的计算参数下得到多种该体系的热力学平衡态相结构。与柔性-半刚性两嵌段共聚物相比，该三嵌段共聚物体系的有序-无序相转变线要高于刚-柔两嵌段共聚物。因此可以说明加入柔性嵌段后，高分子的热力学温度（熔点等）降低。柱状相结构中，半刚性嵌段沿长方形液晶相区的短边方向出现两次折叠。我们的研究为进一步探索高分子折叠现象产生的原因以及液晶成核机理奠定了理论基础。. 采用自洽场场理论方法用于计算柔性-半刚性嵌段共聚物和球形纳米粒子混合体系相行为。通过改变半刚性链的刚柔性、组分的体积分数、Flory-Huggins体系相互作用参数以及纳米粒子大小等参数得到层状相、六角柱状相等一系列一维和二维复合体系的相形态。除此之外，对纳米粒子出现的团聚现象也进行了理论分析。我们的研究为柔性-半刚性嵌段共聚物与纳米粒子的复合体系的制备和应用提供了理论指导。.采用半刚性自洽场理论方法研究了柔性-半刚性嵌段高分子刷在水平基板上的相行为。结果表明，嵌段高分子链随着接枝密度的增加和体系相互作用的增强而被拉直。.采用自洽场理论方法研究了刚-柔嵌段共聚物在三维空间中的纳米微观相结构。结果表明随着温度的降低和刚棒形状由细长变为粗短，嵌段共聚物发生从三维球状相向一维层状相的形态变化。. 采用分子动力学、分子力学等方法预测聚酰亚胺聚合物的热应力、材料的应力应变关系等。以期对热稳定性聚合物的性能对其结构的依赖关系有所掌握。.利用Flory 溶液理论，对湿法纺丝过程中聚酰亚胺-溶剂-非溶剂三相体系的相分离机理进行了研究，建立计算程序，为进一步绘制相图做准备。