Ayou Hao

Roll-to-roll continuous carbon nanotube sheets with high electrical conductivity

Large scale manufacturing of electrically conductive carbon nanotube (CNT) sheets with production capability, low cost, and long-term electrical performance stability is still a challenge. A new method to fabricate highly conductive continuous buckypaper (CBP) with roll-to-roll production capability and relatively low cost is reported. The electrical conductivity of CBP can be improved to 7.6 × 104 S m−1 by using an oxidant chemical (i.e. HNO3 and I2) doping method. To compensate for the conductivity degradation caused by the instability of the oxidant chemical doping, a polymer layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was coated on the chemically doped CBP. The fabricated highly conductive CBP showed stable electrical performance in air for more than a month. This CBP material with high electrical conductivity, relatively low cost, and roll-to-roll manufacturing capability could enable a wide range of engineering applications including flexible conductors, electromagnetic interference (EMI) shielding materials, and electrodes in energy devices.

Characterization at Atomic Resolution of Carbon Nanotube/Resin Interface in Nanocomposites by Mapping sp 2-Bonding States Using Electron Energy-Loss Spectroscopy.

Functionalization is critical for improving mechanical properties of carbon nanotubes (CNTs)/polymer nanocomposites. A fundamental understanding of the role of the CNT/polymer interface and bonding structure is key to improving functionalization procedures for higher mechanical performance. In this study, we investigated the effects of chemical functionalization on the nanocomposite interface at atomic resolution to provide direct and quantifiable information of the interactions and interface formation between CNT surfaces and adjacent resin molecules. We observed and compared electronic structures and their changes at the interfaces of nonfunctionalized and functionalized CNT/polymer nanocomposite samples via scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) spectrum imaging techniques. The results show that the state of sp 2 bonding and its distribution at the CNT/resin interface can be clearly visualized through EELS mapping. We found that the functionalized CNT/polymer samples exhibited a lower fraction of sp 2 bonding and a lower π*/σ* ratio compared with the nonfunctionalized cases. A good correlation between near-edge fine structures and low-loss plasmon energies was observed.

Microstructure and high through-thickness thermal conductivity of graphite fiber composite for structural applications

Combinations of nanoscale and microscale silver particles were used to construct heterogeneously conductive paths in graphite composites for improving through-thickness thermal conductivity. Composites with four different pitch-based graphite fibers were studied and compared to realize the improved thermal conductivity with adequate mechanical performance. The test panels of EWC300X graphite fibers and sliver fillers achieved a through-thickness thermal conductivity of ~10.0 W/m·K at 25 °C. The rheological behavior of Epon862/curing agent resin and silver flakes filled Epon862/curing agent resin was studied for the standardization and quality control of large panel fabrication. By adding 40wt% silver flakes in the resin system, the viscosity greatly increased. The lowest viscosity of 40% silver flakes filled Epon862/curing agent resin system occurred at 65 °C; therefore, the curing process was modified accordingly to ensure resin/fiber wetting and reduction of voids. The hybrid composites with IM7 and pitch-based carbon fiber were also made in order to optimize the composite performance with a balanced thermal conductivity and mechanical properties. The failure mechanisms of laminated composites with and without silver fillers were investigated. The IM7/EWC300X hybrid composite with a density of 2.31 g/cm showed a thermal conductivity of 5.29 W/ m·K and adequate mechanical properties for structural applications.