Highly conductive reduced graphene oxide (GO) polymer nanocomposites are synthesized by a well-organized in situ thermochemical synthesis technique. The surface functionalization of GO was carried out with aryl diazonium salt including 4-iodoaniline to form phenyl functionalized GO (I-Ph-GO). The thermochemically developed reduced GO (R-I-Ph-GO) has five times higher electrical conductivity (42,000 S/m) than typical reduced GO (R-GO). We also demonstrate a R-I-Ph-GO/polyimide (PI) composites having more than 10(4) times higher conductivity (~1 S/m) compared to a R-GO/PI composites. The electrical resistances of PI composites with R-I-Ph-GO were dramatically dropped under ~3% tensile strain. The R-I-Ph-GO/PI composites with electrically sensitive response caused by mechanical strain are expected to have broad implications for nanoelectromechanical systems.

We report an effective way to fabricate mechanically strong and multifunctional polyimide (PI) nanocomposites using aminophenyl functionalized graphene nanosheet (APGNS). APGNS was successfully obtained through a diazonium salt reaction. PI composites with different loading of APGNS were prepared by in situ polymerization. Both the mechanical and electrical properties of the APGNS/ PI composites were significantly improved compared with those of pure PI due to the homogeneous dispersion of APGNS and the strong interfacial covalent bonds between APGNS and the PI matrix. The electrical conductivity of APGNS/PI (3:97 w/w) was 6.6 × 10 −2 S/m which was about 10 11 times higher than that of pure PI. Furthermore, the modulus of APGNS/PI was increased up to 16.5 GPa, which is approximately a 610% enhancement compared to that of pure PI, and tensile strength was increased from 75 to 138 MPa. The water vapor transmission rate of APGNS/PI composites (3:97 w/w) was reduced by about 74% compared to that of pure PI. ■ INTRODUCTIONAromatic polyimide (PI) is a high-performance polymer with applications in the fields of microelectronics, optoelectronics, adhesives, and aerospace owing to its high thermal stability and favorable chemical and mechanical properties. 1,2 However, PI has a few limitations, such as electrostatic accumulation, poor heat dissipation, and low electrical conductivity for special applications. In recent years, much attention has been paid to PI composites with carbon nanomaterials because the incorporation of carbon nanofillers can effectively enhance the thermal, mechanical, and electrical properties of the nanocomposites. 2−6 Graphene, a one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, 7 has revolutionized the scientific frontiers of nanoscience and condensed matter physics due to its exceptional electrical, 8 physical, 9 and chemical properties. 10 The excellent properties of graphene have opened new pathways for developing a wide range of novel functional materials. In addition, graphene has a distinctive mechanical property with fracture strains of ∼25% and a Young's modulus of ∼1 TPa. 9 However, poor dispersion in organic solvents and weak interfacial interactions between graphene and the polymer matrix limit the widespread use of graphene. In contrast, graphene oxide (GO) produced by the oxidation of graphite can solve these issues. It is easily dispersed in water and polar solvents due to the functional groups, such as ketones, diols, epoxides, hydroxyls, and carbonyl, on its edges and basal planes. 11 Nevertheless, GO has limited compatibility with certain polymers and limited solubility in hydrophobic solvent owing to its hydrophilic nature, which can reduce the reinforcement effects of interfacial interaction in the polymer matrix. 12,13 Therefore, the key issue is to improve both the homogeneous dispersion and strong interfacial interaction between the polymer matrix and graphene for the development of high performance polymer/graphene nanocomposites. R...

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