Study On Aggregation Structure Of Polyimide/Silica Nano-Hybrid Film

Recently, great attentions have been focused, mainly, on the preparation of polyimide/silica (PI/SiO₂) nano-hybrid films and properties such as mechanical property, thermal stability and so on. But there were seldom systematical researches about the influences of different incorporating conditions on the aggregation structure, and the perfect study system has not been formed about the relationship between properties and aggregation structure of PI/SiO₂ nano-hybrid films.In present study, polyamic acid/silica solutions were synthesized via Sol-Gel route by the hydrolysis and condensation of tetraethoxysilane (TEOS) that served as the precursors of the inorganic moiety and produced the silica nano-particles in-situ in the polyamic acid solution (PAA) based on the stepwise polycondensation of pyromellitic dianhydride (PMDA) and 4, 4′-oxydianiline (ODA) in N, N-dimethylacetamide (DMAc). PI/SiO₂ hybrid film was obtained by casting PAA/silica solution onto glass substrate, followed by thermally imidizing. The chemical structure and aggregation structure of PI/SiO₂ films were respectively characterized by Fourier Transform Infrared Spectroscope (FT-IR), Atomic Force Microscope (AFM), Scanning Electronic Microscope (SEM), Wide-angle X-ray Diffraction (WAXD). The influence of solid content of PAA hybrid solutions, deionized water content, solvent and thermal imidization process on the aggregation structure of PI/SiO₂ nano-hybrid films was studied. All results indicated that PI/SiO₂ nano-hybrid films have been prepared by schematic route of this experiment successfully. The aggregation structure of PI/SiO₂ nano-hybrid film was influenced by four kinds of technical parameters above. The sizes of silica particles increased with solid content increasing in a certain content range. The content of deionized water was very important to the aggregation structure of PI/SiO₂ nano-hybrid films. In the eight kinds of solvents system, the sizes of silica particles were the smallest, and the interface between organic and inorganic phases was obscure using N-methyl-2-pyrrolidone (NMP)/ dimethyl benzene as solvent. In thermal imidization process, it is all effective methods to reduce silica particle size that extending residence time at 60oC, improving final temperature to 350oC, extending residence time at 350oC and reducing heating rate in high temperature area.