Preparation Of Functional Polyimide Nanocomposite Films And The Properties Investigation

Polyimide/nanoparticles composite films,which combine the excellent performances of polyimide such as thermal stability,mechanical property, chemical stability and the unique functions of nanoparticles used in the optical, electrical and magnetic field.In this dissertation,we report our efforts on the preparation of functional polyimide nanocomposite films with superparamagnetism,electrical conductivity and high dielectric constant via various methods.Factors influencing the preparation of composite films were investigated.The surface morphology,dispersion of nanoparticles and related properties of composite films were characterized.Fe₃O₄ nanoparticles have been prepared by chemical co-precipitation method and modified by coupling agent to incorporate amido groups on the particle surface.Poly(amic acid) molecular chain can be grafted onto the particle surface to avoid the aggregation of nanoparticles by utilizing the interaction between the amido groups on particle surface and the anhydride groups of monomer.X-ray diffraction(XRD),transmission electron microscope(TEM) and scanning electron microscope(SEM) were carried out on the crystal conversion of Fe₃O₄ nanoparticles and their dispersion in the bulk matrix and on the film surface.The result indicated that during the thermal curing process,Fe₃O₄ was oxidized to Fe₂O₃,and the distribution of magnetic nanoparticles in the final polyimide films looks like "clouds" with different size,but the film exhibited typical superparamagnetic response.Polyimide/Fe₂O₃ nanocomposite film has been prepared using 3,3',4,4'-benzophenonetetracarboxylic dianhydride /4,4'-oxydianiline (BTDA/ODA) and pyromellitic dianhydride/4,4'-oxydianiline(PMDA/ODA) based polyimide as the matrix and iron(â…¢) 2,4-pentanedionate(Fe(acac)₃) as the nanoparticles precursor via in situ technique.During the thermal curing process,Fe(acac)₃ decomposed to iron oxide and then crystallized in polyimide matrix.We found that the chemical structure of polyimide have influenced the size and morphology of the formed Fe₂O₃ nanoparticles.For the BTDA/ODA based polyimide matrix,we got Fe₂O₃ nanocube with an average diameter of 26 nm.While for the PMDA/ODA based polyimide matrix,the diameter of Fe₂O₃ nanoparticles was ca.10 nm and the shape was irregular. However,both of the two systems exhibited superparamagnetic behavior.We have used two methods to endow the polyimide/Fe₂O₃ nanocomposite films with electrically conductive property.The first one was that with the in-situ single-stage self-metallization protocol,surface silvered polyimide films were prepared using(1,1,1-trifluoro-2,4-pentadionato) silver(AgTFA) as the silver precursor.The poly(amic acid)/silver salt solution was cast onto the polyimide/Fe₂O₃ composite films.The silver layer on the film surface was established by the migration and aggregation of silver particles formed during the thermal treatment,and the surface sheet resistivity was ca.0.1Ω/â–¡.The other method was that with surface modification and self-metallization protocol,polyimide/Fe₂O₃ films were surface modified by alkaline aqueous solution,and then immersed into the silver salt solution to perform the ion exchange reaction with silver ions.Subsequently,silver ions were reduced by the base glucose aqueous solution.Surface differences were observed on the metallized film,that is,a continuous silver layer has formed on the upside surface with maximum reflectivity of 76.15%and surface resistance of 0.7Ω/â–¡.While only a small amount of silver particles dispersed on the underside surface.Polyimide/copper composite films were prepared using commercial polyimide films as the matrix via surface modification,ion exchange and followed by the polyol reduction technique.FTIR and ICP were carried out on the surface modification and ion exchange process.The formation of copper nanoparticles during the reduction process was observed.We found that copper nanoparticles uniformly dispersed in the whole modified layer and reached to the stable diameter value of 27 nm at the reduction time of 15 min. If we directly treat the copper ions contained film in the ambient circumstance, polyimide/cupric oxide composite films can be obtained.A continuous cupric oxide layer was formed on the film surface.The influence of thermal curing time and etching time on the formation of cupric oxide layer was investigated. And the mechanism pertaining to the cupric oxide layer formation has been discussed.Polyimide/barium titanate(BaTiO₃) composite films have been fabricated using PMDA/ODA based polyimide as the matrix.The effect of BaTiO₃ particles content on the dielectric behavior was traced.For the sample measured at the frequency of 10⁴ Hz,the dielectric constant was 17.81 for the BaTiO₃ content of 70 wt%.Three-phase polyimide/BaTiO₃/silver nanocomposite film was fabricated using AgTFA as the silver precursor via in-situ single-stage self-metallization technique.Uniform dispersion of silver nanoparticles in the film can be realized by controlling the thermal imidization time and temperature.For the sample measured at the frequency of 10⁴ Hz,the dielectric constant was 13.72 for the BaTiO₃ content of 30 wt%and the silver content of only 2 wt%.