基于异质结构氟化石墨烯制备高能量密度聚酰亚胺复合薄膜

Maintaining polyimide's (PI) high performance and improving the dielectric strength and constant synergistically is still a challenging topic in the area of advanced PI dielectric materials. In this work, nitrogen atoms that are pre-doped into graphene sheet are employed to catalyze the fluorination of adjacent carbon atoms in graphene. The C-F bonds aggregate in the vicinity of doped nitrogen atom forming fluorinated region, while the un-fluorinated carbon atoms generate the aromatic region. As a result, the as-prepared fluorinated graphene (FG) presents heterostructure that is composed of fluorinated region and aromatic region. In this case, the covalent bonding nature of C-F bonds is enhanced, which thus improve the grafting reactivity of C-F bonds in the partly fluorinated FG. The fluorination reaction of nitrogen doped graphene is thoroughly studied aiming to reveal the influence of nitrogen on fluorinating mechanism, C-F distribution, and bonding nature. Then, the C-F bonds are allowed to react with PI under the reduction effect of solvent during the composite process, making the grafting of PI macromolecules on the FG sheets. The fluorinated region of FG is consequently transformed into a “grafted fluorinated region” containing grafted PI macromolecules and residual C-F bonds. This enhances the interface compatibility of composite film and inhibits the accumulation of space charge at interface. Meanwhile, the grafted fluorinated regions isolate the aromatic regions and prevent their accumulation. Therefore, the dielectric strength of the composite film is expected to be enhanced. In addition, the highly polarizable π-electron in the aromatic regions and microcapacitor structure in the composite film are used to improve the dielectric constant and thus prepare high performance PI film with a high energy density. Herein, the dielectric confinement and homogenizing space charge effect of the new heterostructure composed of grafted fluorinated region and aromatic region are explored in order to elucidate the relationship between the structure and the dielectric properties of PI/FG composite film. It is hoped that these findings can provide a reference for the preparation of high performance dielectric materials with a high energy density.

本项目针对如何在保持聚酰亚胺（PI）高性能的同时协同提高介电强度和介电常数的难点问题，首先，利用石墨烯中预先引入的氮杂原子催化周围碳原子氟化反应，促使C-F局部聚集，制得氟化区和芳香区共存异质结构FG，以提高C-F共价键属性，克服低氟化FG的C-F无法发生接枝反应的缺点；明晰氮杂原子对氟化反应历程、C-F分布和价键属性的影响规律。然后，通过C-F共价键在溶剂还原效应下与PI的界面接枝反应，促使FG氟化区转变成接枝PI分子和残留C-F共存的“接枝氟化区”，增强复合界面相容性、抑制空间电荷聚集，并“隔离”芳香区，防止其堆积，进而提高介电强度；同时，利用芳香区中π电子及其微电容结构提高介电常数。最终，制得高能量密度高性能PI薄膜。探究复合薄膜中FG接枝氟化区与芳香区共存异质结构的介电限域和空间电荷均化效应，及其对介电强度和介电常数的影响规律和机制，为制备高能量密度的高性能介电储能材料提供借鉴。

针对如何在保持聚酰亚胺（PI）高性能的同时协同提高介电强度和介电常数的难点问题，本项目利用石墨烯中预先引入缺陷催化周围碳原子的氟化反应，制得氟化区和芳香区共存异质结构氟化石墨烯（FG）新材料，然后通过FG复合改性PI，利用异质结构FG中氟化区宽带隙、低LUMO能级的特点提高PI介电强度，利用被“隔离”开的芳香区结构调控介电常数和介电损耗，提供解决上述问题的新思路和新方法。本项目具体围绕以下三点开展研究工作：①异质结构FG的制备技术及氟化化学反应研究，②FG溶剂作用下的还原接枝反应研究，③PI/FG复合工艺与复合材料结构/性能研究。在实现高效可控地在石墨烯骨架内引入碳杂原子的基础上，明晰了氮杂原子对氟化反应历程、C-F分布和价键属性的影响规律，形成了制备异质结构FG的新方法；并利用FG可控还原的“逆向工程”，以及孔洞缺陷结构的催化作用，分别实现了异质结构FG的制备；并利用EPR分析和纳米石墨烯模型分子的方法分析了石墨烯类材料氟化反应机理探究。探索了FG的Suzuki反应，高密度官能化反应，以及其与PAA原位接枝反应的规律。通过聚酰胺酸（PAA）与FG复合制备PI/FG复合材料以及可溶性PI与FG复合效应研究，建立了FG/PI分子结构/界面结构与FG/PI复合材料介电性能的关系，形成了对介电强度和介电常数的调控机制。从而整体上理解了异质结FG制备和复合应用中的基本物理和化学问题，为新型FG材料制备及其在复合材料领域的创新应用提供了较坚实的前期研究基础。另外，本项目拓展研究了FG在湿气发电、润滑油改性剂方面的新应用，明确纳米纤维素的氟化反应特性，建立了复合平面型小分子形成界面陷阱异质结构提高聚酰亚胺储能密度的新方法，实现了高性能PI/FG复合泡沫和PTFE/FG复合材料的制备。本项目目前在学术期刊上共发表SCI收录论文18篇（其中第一标注9篇，第二标注5篇，第三标注2篇）；申请或授权国家发明专利5项（其中授权3项）；培养博士研究生和硕士研究生6名，其中已毕业硕士生3名。