刚性链体系纳米粒子空间分布调控及其链段弛豫行为研究

Tuning the spatial distribution of nanoparticles is a principal method for fabricating polymer nanocomposites with multiscale and multifunctional high-order structure. In this proposal, polyimide (PI) consisting of a rigid imide benzene backbone structure is chosen as a model system. We will mainly investigate the regulation mechanism of the entropy-induced phase separation through controlling the grafting chain length and density, and track the condensed structure evolution of nanoaprticles caused by the restricted entropy of the grafting chains. We will try to get comprehensive characterization information of the effect of nanoparticle size, the degree of polymerization of the matrix and its polydispersity, casting solvent and thermal annealing on the nanoparticle dispersion morphology evolution. The rigid polymer composite morphology diagram will be established. Furthermore, by means of broadband dielectric analysis, solid-state NMR T2 spectrum and dynamic rheological measurements, we will mainly systematically study the influence of the grafted chains on the molecular layer thickness with interfacial confinement and cooperative glass transition behavior of the nanocomposites. The relationships between segmental relaxation and nanoparticle spatial distribution of PI based nanocomposites will also be probed. Besides, the correlation between the interfacial interactions, the spatial dispersion of nanoparticles, the segmental relaxation and the macroscopic properties of the rigid molecular chain composite system will be revealed. The results of our proposal is not only potentially helpful for us to further understand the condensed structure of rigid polymer chains nearby nanoparticles, but also theoretically and practically important for fabrication of multifunctional and high performance PI based nanocomposites.

纳米粒子空间分布调控是构建纳米复合材料多尺度、多功能高次结构的重要手段。本项目以主链带刚性酰亚胺环的聚酰亚胺（PI）为研究对象，重点考察刚性分子链接枝纳米SiO2体系接枝链长度、密度、分布对分子链间熵致自憎诱导的相分离行为、以及纳米粒子因接枝链受限熵变引起的凝聚结构演变的调控作用，探讨纳米粒子粒径、PI基体分子链长度及分布、复合体系溶剂化效应和复合熔体等温处理等因素对纳米粒子空间分布的影响，绘制刚性链体系纳米粒子的空间分布相图。在此基础上，结合宽频介电谱、固体核磁共振T2谱和动态流变测试，深入分析刚性接枝链对界面受限分子层厚度及其玻璃化协同转变行为的影响，阐明刚性链体系界面相互作用-纳米粒子空间分布-链段弛豫的内在关联。项目的开展，不仅有助于深入理解纳米粒子周围刚性分子链的凝聚态结构，而且掌握刚性链体系纳米粒子空间分布调控规律还可以为PI纳米复合材料的进一步高性能和多功能化提供理论指导。

调控纳米粒子的分散以及阐明界面作用与宏观性能之间的内在联系是纳米复合材料高性能多功能化的两大关键问题。本项目基于聚合物复合材料纳米粒子可控分散、链段弛豫及其性能关联开展工作，主要结果如下：(i) 采用“impurity-free”无界面污染法实现了纳米粒子在刚性链体系聚酰亚胺 (PI) 中的均匀分散，增强了粒子与基体的界面强度，大大提高了材料的力学性能。(ii) 系统研究了刚性链PI接枝纳米粒子在PI基体中的空间分布与链段弛豫行为。结果表明，复合粒子以细小团簇体分散于基体中，接枝链与基体链间相互渗透，复合体系玻璃化转变温度升高，链段运动受限。且较长接枝链的纳米粒子与基体相互作用越强，有利于同时提高复合体系力学强度和韧性。(iii) 考察了半刚性链体系聚苯乙烯接枝链聚合度、接枝链密度、基体链聚合度以及接枝链与基体链相容性对纳米粒子空间分布的影响规律，揭示了纳米粒子周围接枝链和基体链的界面层弛豫行为。(iv) 研究了接枝氧化石墨烯粒子在结晶性聚乳酸体系中的分散特性及其对结晶性聚合物宏观性能的影响规律。(v) 揭示了界面相互作用 (氢键作用与物理吸附) 对粒子填充体系界面层链段动力学影响规律的区别。(vi) 通过改进的乳液共混和原位还原法，成功解决了阴离子乳液体系中石墨烯易团聚难题，实现了纳米级均匀分散，考察了辐照条件下复合体系链段弛豫行为，揭示了石墨烯的自由基猝灭机理。