Qing Yan

Tough Graphene−Polymer Microcellular Foams for Electromagnetic Interference Shielding

Functional polymethylmethacrylate (PMMA)/graphene nanocomposite microcellular foams were prepared by blending of PMMA with graphene sheets followed by foaming with subcritical CO(2) as an environmentally benign foaming agent. The addition of graphene sheets endows the insulating PMMA foams with high electrical conductivity and improved electromagnetic interference (EMI) shielding efficiency with microwave absorption as the dominant EMI shielding mechanism. Interestingly, because of the presence of the numerous microcellular cells, the graphene-PMMA foam exhibits greatly improved ductility and tensile toughness compared to its bulk counterpart. This work provides a promising methodology to fabricate tough and lightweight graphene-PMMA nanocomposite microcellular foams with superior electrical and EMI shielding properties by simultaneously combining the functionality and reinforcement of the graphene sheets and the toughening effect of the microcellular cells.

Vacuum-assisted synthesis of graphene from thermal exfoliation and reduction of graphite oxide

We report a vacuum-assisted method for thermal exfoliation and in situreduction of graphite oxide in large quantity at a temperature as low as 135 °C. The resulting graphene sheets contain only few-layered sheets with an average thickness of 0.9 nm, and their specific surface area (758 m2 g−1) is comparable to that of conventional graphene generated at 1050 °C at atmospheric pressure (700 m2 g−1). The in situ thermal reduction during the exfoliation process was confirmed by the increased C/O atomic ratio compared to that of graphite oxide. The restoration of the graphitic sp2 network makes it highly efficient in improving the electrical conductivity of polymers at a low graphene loading.

Surface structural evolvement in electrochemical oxidation and sizing and its effect on carbon fiber/epoxy composites properties

An evolvement of surface physicochemical structure in the process of electrochemical oxidation and sizing treatment was monitored by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. An effect of this evolvement on the properties of carbon fiber/epoxy composites was also researched. The results showed that the root mean square roughness increased from 4.6u2009nm for untreated fibers to 9.1u2009nm for surface-treated fibers, and the root mean square value of sized fibers decreased to 8.5u2009nm. The relative contents of oxygen and nitrogen atomic on carbon fiber surface increased obviously after electrochemical oxidation. Oxygen atomic concentration took a further improvement after sizing treatment and only hydroxyl functional group was found on its surface. The interfacial strength between carbon fiber and the resin matrix improved after surface electrochemical oxidation and sizing, and the mechanical interlock was considered to be the governing factor in fiber/resin adhesion of carbon fiber/epoxy composites.

Electrical Conductivity of Melt Compounded Functionalized Graphene Sheets Filled Polyethyleneterephthalate Composites

Graphene, monolayer of carbon atoms arranged in a honeycomb network, has recently gained revolutionary aspirations (Novoselov et al., 2005; Novoselov et al., 2007; Heersche et al., 2007; Zhang (a) et al., 2005; Stankovich et al., 2006) because of its remarkable electronic properties (Zhang (b) et al., 2005; Berger et al., 2004), unusual thermal properties (Balandin et al., 2008) and good mechanical properties (Lee et al., 2008). These extraordinary properties make it an excellent choice as inorganic fillers to substantially improve electrical, thermal and mechanical properties of composite materials (Stankovich et al., 2006; Ramanathan et al., 2008). Several effective techniques have been developed for preparing graphene nanosheets, including chemical (Stankovich et al., 2006) and mechanical exfoliation (Novoselov et al., 2004), alkali metals intercalation and expansion (Viculis et al., 2003), microwave chemical vapor deposition (Wang et al., 2009), substrate-based thermal decomposition (Berger et al., 2004), and thermal exfoliation of graphite oxide (GO) (McAllister et al., 2007). Among them, chemical reduction of exfoliated graphite oxide in the presence of a surfactant or polymer is a relatively new method to prepare electrically conductive individual graphene sheets. Stankovich (Stankovich et al., 2006) put forward a new process to produce polystyrene/graphene nanocomposites via ultrasonic exfoliation and chemical reduction of graphite oxide and molecular-level dispersion of chemically modified graphene nanosheets. In addition, the thermal exfoliation and in situ reduction method can conveniently produce graphene nanosheets for mass production. As confirmed by Aksay and co-workers (McAllister et al., 2007), in situ reduction reaction took place during the thermal exfoliation process, which converted insulating graphite oxide to conducting graphene. More importantly, the graphene resulted through thermal exfoliation still contained some oxygen-containing groups. The oxygen functionalities on the graphene nanosheets will facilitate their dispersion in polar polymers (Ramanathan et al., 2008). Effective medium approximation indicated that graphene is more effective in improving conductivity of composites than carbon nanotubes (Xie et al., 2008). The polystyrene/graphene nanocomposites prepared by chemical modification and reduction in

Effects of Fillers on the Tensile Properties of Polyimide Composite Films at Room and Cryogenic Temperatures

Nano- and micro-filler reinforced polyimide composite films with a high thermal conductivity and a low thermal expansion while still remaining high modulus and strength are desirable in cryogenic applications. Polyimide composite films were prepared by incorporation of fillers such as clay and silica particles into polyimide matrix. The silica particles were made by sol-gel process. The tensile properties of polyimide composite films were studied at room and cryogenic temperatures (77K) taking into account the effects of filler contents for involved fillers. SEM study was carried out on the fracture surfaces of the polyimide composite films. The results for the dependence of the tensile properties ofpolyimide composite films at room and cryogenic temperatures were discussed on filler contents for the involved fillers.