Preparation Of Surface Functionalized Polyimide Composites And Structure And Property Investigation

Polyimide (PI) is an important high-performance polymer widely used in aerospace, microelectronics, communication fields and so on for their marked thermal-stability, excellent mechanical, electrical and radiation-resistance properties. With the development of science and technology, new requirements for the material such as high performance, multi-functional and low cost are raised. Combining inorganic nanoparticles especially metal or metal oxide nanoparticles with polyimide is an important approach to realize the functionalization of the polyimide materials. The prepared polyimide composite materials not only have the excellent performances of polyimide but also possess the unique optical, electrical, magnetic or catalytic functional properties of metal or metal oxide nanoparticles, and they have great potential applications in microelectronic, aerospace and other fields. In this thesis, based on the hydrolysis characteristics of polyimide matrix in alkali, various polyimide/metal or metal oxide functional composites were prepared via different surface modification methods utilizing polyimide films or fibers as matrix and inorganic metal salts as metal source. Factors influencing the surface morphology, thermal, mechanical and functional properties such as electric, magnetic and optical properties of the composites were studied and the related mechanisms were also investigated.Semiconductive PI/cobalt oxide (Co3O4) magnetic composite films were prepared by surface modification, ion exchange and thermal treatment in air atmosphere using commercial pyromellitic dianhydride/4,4'-oxydianiline (PMDA/ODA)-based polyimide films as the substrate and cobalt nitrate as the cobalt source. Continuous cobalt oxide layers could be obtained on the PI surface layer by controlling appropriate preparation conditions and the room temperature surface resistance of the composite film was in the range of 107Ω The particle size of cobalt oxide was in the range of 15-40 nm. The effect of cobalt ion loading on the morphology and properties of the composite films were investigated and the possible formation mechanism of continuous cobalt oxide layer was also proposed. The PI/Co3O4 composite films maintained the excellent thermal and mechanical properties of the bare polyimide film. The adhesion between surface cobalt oxide composite layer and the PI matrix was acceptable.PI/ZnO nanocomposite films were prepared by the surface modification and ion exchange technique using PMDA/ODA-based PI films as the substrates and zinc nitrate as the precursor of ZnO. The formation and growth process of ZnO nanoparticles and the photoluminescence (PL) properties of the composite films during thermal treatment were tracked. The results revealed that the formation and growth of ZnO nanoparticles were a slower process compared with other metal oxides and the ultraviolet emission band of ZnO would not appear on the PL spectrum of the composite film unless the thermal treatment time at 350℃is extended to 7 h. In addition, the effect of alkali treatment and ion exchange conditions were investigated in relating to the amount of zinc ion loading, surface morphology, photoluminescence and thermal property of the PI/ZnO composite films. The PL spectra of all the PI/ZnO nanocomposite films obtained at 350℃/7 h possessed a weak ultraviolet emission peak and a broad and strong visible emission band. The composite film kept the excellent thermal properties of the host PI film.PI/NiO composite films were prepared by the surface modification and ion exchange method. The formation and aggregation of NiO nanoparticles during thermal treatment may be accompanied by the decomposition of nickel polyamate and oxidative degradation of surrounding PI matrix catalyzed by newly generated NiO nanoparticles. Therefore, many large micron-wide cracks with dentritic shape occurred on the PI film surface. When the urea deposition process was introduced between ion exchange and thermal treatment, PI/NiO composite films without evident defects can be obtained. The effects of alkali treatment, urea treatment and thermal treatment conditions on the morphology and thermal properties of the composite films were investigated. XPS characterization demonstrated that nickel hydroxide particles were formed on the PI film surface after urea deposition process and converted to cubic nickel oxide nanoparticles with an average size of about 10-15 nm after thermal treatment in air atmosphere. The PI/NiO composite film presents ferromagnetic properties at room temperature. The composite films kept the excellent thermal stability of host polyimide film. When the deposition process of nickel ion-doped polyimide film was performed in dilute ammonia solution at room temperature, polyimide composite films with nickel NiO nanoparticles homogenously dispersed on both surface layers can also be obtained.Surface silvered PI films were prepared at room temperature by surface modification, ion exchange and reduction in ascorbic acid solution utilizing 1 PMDA/ODA-based PI films as the substrate and silver nitrate as the silver precursor. The morphology, conductivity and reflectivity of the both surfaces of the PI/Ag composite film were investigated in relating to alkali treatment time and reduction time. Film with maximum surface resistance of less than 1Ω/□and maximum reflectivity of 92.97% and 83.55% could be achieved. Surface silvered polyimide fibers were fabricated by the same method using polyimide fibers prepared in our laboratory as substrate and silver nitrate and silver ammonia complex cation as the silver source respectively. The effect of alkali treatment conditions and ion exchange conditions on fiber surface morphology, conductivity and mechanical properties were studied. Continuous silver layer can be formed on polyimide fiber surface and the surface resistances of the composite fibers could be reached to 102 Q/cm. Compared with silver nitrate, silver ammonia complex cation has higher efficiency for polyimide silver metallization which can be achieved by employing very dilute silver ion solution (0.04 M) and very short ion exchange time (5 min). The surface silvered polyimide films and fibers essentially maintained the mechanical properties of host polyimide films and fibers and the surface silver layers were well adhered to the polyimide substrates.