Mechanically Strong and Multifunctional Polyimide Nanocomposites Using Amimophenyl Functionalized Graphene Nanosheets

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 <i>in situ</i> 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 10¹¹ 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

Grafting of Polyimide onto Chemically-Functionalized Graphene Nanosheets for Mechanically-Strong Barrier Membranes

A series of polyimide (PI) nanocomposite films with different loadings of aminophenyl functionalized graphene nanosheets (AP-rGO) was fabricated by in situ polymerization. AP-rGO, a multifunctional carbon nanofiller that can induce covalent bonding between graphene nanosheets and the PI matrix, was obtained through the combination of chemical reduction and surface modification. In addition, phenyl functionalized graphene nanosheets (P-rGO) were prepared by phenylhydrazine for reference nanocomposite films. Because of homogeneous dispersion of AP-rGO and the strong interfacial interaction between AP-rGO and the PI matrix, the resulting nanocomposite films that contained AP-rGO exhibited reinforcement effects of mechanical properties and oxygen barrier properties that were even better than those of pure PI and the reference nanocomposite films. In comparison to the tensile strength and tensile modules of pure PI, the composite films that contained AP-rGO with 3 wt % loading were increased by about 106% (262 MPa) and 52% (9.4 GPa), respectively. Furthermore, the oxygen permeabilities of the composites with 5 wt % filler content were significantly decreased, i.e., they were more than 99% less than the oxygen permeability of pure PI

In Situ Synthesis of Thermochemically Reduced Graphene Oxide Conducting Nanocomposites

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 10⁴ 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

Chemical Method for Improving Both the Electrical Conductivity and Mechanical Properties of Carbon Nanotube Yarn via Intramolecular Cross-Dehydrogenative Coupling

Chemical post-treatment of the carbon nanotube fiber (CNTF) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl₃ at room temperature. The Raman intensity ratio of the G band to the D band (<i>I</i>_G/<i>I</i>_D ratio) of CNT fiber increased from 2.3 to 4.6 after ICDC reaction. From the XPS measurements, the <i>A</i>_CC/<i>A</i>_C–C ratio of the CNT fiber increased from 3.6 to 4.8. It is of keen interest that both the electrical conductivity and tensile strength of CNT yarn improved to 3.5 × 10³ S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn

Carbon Nanotube Core Graphitic Shell Hybrid Fibers

A carbon nanotube yarn core graphitic shell hybrid fiber was fabricated <i>via</i> facile heat treatment of epoxy-based negative photoresist (SU-8) on carbon nanotube yarn. The effective encapsulation of carbon nanotube yarn in carbon fiber and a glassy carbon outer shell determines their physical properties. The higher electrical conductivity (than carbon fiber) of the carbon nanotube yarn overcomes the drawbacks of carbon fiber/glassy carbon, and the better properties (than carbon nanotubes) of the carbon fiber/glassy carbon make up for the lower thermal and mechanical properties of the carbon nanotube yarn <i>via</i> synergistic hybridization without any chemical doping and additional processes