Fabrication And Properties Of Graphene/Polyimide Flexible Composite Film

For the overall performance o f outstanding mechanical properties, thermal stability, low dielectric properties and chemical resistance, Polyimide(PI) have been widely used in microelectronics, membranes, coatings, aerospace and adhesives etc. Fields. For the rigid polymer backbone structure and strong inter-molecular forces in raditional PI molecular chains, the accumulation o f polymer molecular chains is very close, and generally have poorly soluble, refractory molding processing difficulties and other shortcomings. Although alicyclic PI have been able to overcome the deficiencies caused by the wholly aromatic PI, but introduces new problems. Alicyclic PI generally have poor mechanical and thermal properties which may limit its use in some areas.Graphene is a new carbon material. Its overall performance in all aspects caused very high concern since it been found and become the darling o f research. Graphene has excellent optical, electrical, thermal and mechanical properties for its unique two-dimensional monolayer structure, which just can be used to improve the defects performance o f polyimide. In view o f the above theoretical considerations, we can choose graphene to improve the properties o f the polymer materials, and prepare the graphene based nanocomposite. However, there is a strong inter-molecular interaction forces in graphene sheets, which makes graphene molecules are prone to self-agglomeration. This phenomenon is very detrimental for its uniformly dispersed in PI, and thereby affecting the graphene to improve the performance o f the polymer. Thus, our experiment was envisaged to improve polymer properties, while the choice o f different flexibility o f polymer chains to investigate the effect o f a flexible polymer in the graphene dispersion.Our research work was mainly as follows:Firstly, natural graphite powder was oxidized by the modified Hummers method to give a graphite oxide, and then ultrasonic peeling, centrifugation, to obtain a derivative o f graphene-graphene oxide(GO) suspension, and then with hydrazine hydrate(N2H4) reductant to give the final product-reduced graphene oxide(RGO).Secondly, use 4?4,-diaminodiphenyl ether(4,4,-ODA) and biphenyl dianhydride(BPDA) as the synthesis precursor, prepared RGO/PI nanocomposite films with different contents o f RGO. As a comparative experiment, we changed RGO to GO and prepared GO/PI nanocomposite films by the same method with corresponding percentage o f GO. Then we tested the dielectric properties, thermal properties and mechanical properties of the two series of materials, followed by a comparison. We found that the addition of graphene significantly enhanced the conductive properties of the polymer, while the tensile modulus, tensile strength and storage modulus(Ef) of polymers were also improved significantly. In the addition level of l.Owt% at the temperature o f 60°C, the storage modulus of GO/PI film was 2525.4MPa, while the RGO/PI film was 2844.9MPa, increased by 119.1% and 146.8% then the pure PI respectively, and the loading o f RGO was the most obvious.Thirdly, we prepared three series o f composite films with different flexible, for the reaction of 4,4-ODA, 1,1- bis [4-(4-aminophenoxy) phenyl] cyclohexane(BAPCH) and 1,1-bis [4-(4-amino-2-trifluoromethyl-phenoxy) phenyl] cyclohexane(BATFPCH) with BPDA, respectively(with the same adding of RGO), and then their performances were tested, followed by a comparative study. We found that the conductive performance of the three series o f composites have significantly improved by the RGO adding. Meanwhile, the introduction of cyclohexyl structure and CF3 in the polymer main chain was highly effective to enhance the optical properties of the material, as well as the reduce of water absorption. There was a weakening effect for the rigid o f materials on the introduction o f CF3, but when you add the more amount of RGO, this weakening effect may become negligible. Thus, the mechanical properties of the materials began to deteriorate significantly. Therefore, we can moderately improve the mechanical properties of the alicyclic PI by the controlling of the addition of RGO content.Finally, three series of novel flexible polymer nanocomposites were synthesized through polymerization of a flexible ODPA with three diamine(4,4’-ODA, 1,1- bis [4-(4-aminophenoxy) phenyl] cyclohexane(BAPCH) and 1,1-bis [4-(4-amino-2-trifluoromethyl-phenoxy) phenyl] cyclohexane(BATFPCH))which were involved in the above experiments, and simultaneously with the addition of graphene. Combined w ith the above experimental results, we further demonstrated that the flexibility o f polym er chain was influential for the uniformly dispersed o f graphene in polymers.