Weijian Xiong

Liquid crystal functionalization of graphene nanoplatelets for improved thermal and mechanical properties of silicone resin composites

A liquid crystalline molecule, polyurethane-imide (PUI), was used to functionalize graphene nanoplatelets (GNS) via covalent bond and π–π interactions. The PUI functionalized graphene nanoplatelets (PUI–GNS) were characterized by fluorescence spectroscopy, thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy, and then mixed with silicone resin as fillers to fabricate silicon resin nanocomposites. The drastic quenching of the PUI fluorescence elucidated that the biphenyl anchoring unit of liquid crystalline PUI was strongly interacted with the surface of graphene sheets via π–π interactions. FTIR and Raman spectroscopy proved the existence of a covalent interaction between the PUI and GNS. The mechanical properties testing indicated that the tensile strength of silicon resin nanocomposites increased by 521% over that of a neat silicon resin when the mass fraction of PUI–GNS was 1.0%, and the elastic modulus of the silicon resin nanocomposite increased by 902% over that of the neat silicon resin if it came up to 2.0%. The thermal conductivity of the resin filled with the PUI–GNS was improved to be 1.3822 W (m K)−1 at a mass fraction of 10.0%, which was enhanced more than 16.5 times over that of the neat silicon resin. The resulting thermally conductive and mechanically applicable silicon resin nanocomposites could be significant in a wide variety of electronic packaging applications.

Preparation and thermo-mechanical properties of functionalized graphene/silicone rubber nanocomposites

Silicone rubber is widely used in electronic packaging materials. Electronic appliances have become miniaturized which need more outstanding packaging materials. Functionalized grapheme/scilicon rubber composites is one of the development to improve the performance of the silicone rubber. Graphite oxide (GO) was modified by KH-550, and then the modified graphite oxide was reduced by hydrazine hydrate to get functionalized graphene (FG). In order to get functionalized graphene /silicon rubber nanocomposites, FG was dispersed into 107 gum. The structure and morphology of both the nanocomposites and FG were characterized by FTIR, SEM, XRD and TG. The results show that KH-550 was bonded with GO, the layer of FG was expanded to 0.4nm. Compared with the pure silicon rubber, the initial decomposition temperature of all the functionalized graphene/silicon rubber nanocomposites were improved. Mechanical property tests show that the tensile strength of the nanocomposites with 0.7wt% FG are 2.46 MPa which increases by 198.39% compared with neat silicone rubber, and the elongation at break of composite increases by 171.89%, which is about triple of the pure silicone rubber. Thermal conductivity test shows that the thermal conductivity of the composites with 1.0wt% FG reaches 0.18 W /(m·K).

Preparation of graphene aerogel and its electrochemical properties as the electrode materials for supercapacitors

Graphene oxide was prepared through an improved method, and then three-dimensional graphene aerogel was (GA) synthesized by an organic sol-gel process. The morphological characteristics and textural properties of the GA were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrum (FT-IR), respectively. For capacitive properties tests, cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) were carried out in a two-electrode system with a working potential window from 0 to 1V. Moreover, a specific capacitance of 176 F/g was determined at a constant current density of 1 A/g in 1 mol L-1 Na2SO4 electrolyte. The advantageous properties such as high specific surface areas, high specific capacitance, high conductivity and well-connected 3D mesoporous structure of the GA, permit excellent performance as electrode materials for supercapacitors.

Fast single mode microwave-assisted synthesis of porous carbon aerogel for supercapacitors

Carbon materials are, in general, very good absorbents of microwaves. The microwave-assisted synthesis illustrated in this work allows carbon aerogels (CA) to be synthesized in a much shorter time than by conventional methods. Resorcinol-formaldehyde xerogels were synthesized using single mode microwave synthesis system at 85°C for less than an hour. Then, carbonization was performed to obtain carbon xerogels. The effect of the microwave radiation time involved in the process on the textural and electrochemical performance of the final materials was evaluated. It can be concluded that it is possible to control their textural characteristics of carbon xerogels by modifying radiation time. The electrochemical performance of synthesized carbon xerogels as electrode materials in electric double-layer capacitors was studied by cyclic voltammetry and charge/discharge experiments in an alkali medium (6MKOH). It can be seen that single mode microwave-assisted synthesis helps the carbon xerogels display good cycle durability and the specific capacitance of the CA which was radiation for 40minutes is 96.22F/g even without any activation and doping treatments.

Sol-gel synthesis of Li 2 MnSiO 4 /C nanocomposite with improved electrochemical performance for lithium-ion batteries

In recent years, modifying anode materials surfaces of Li₂MnSiO₄ become a popular pursuit. This paper reveals a fast sol-gel process that the Li₂MnSiO₄ in situ coated with carbon membrane prepared using liquid polyacrylonitrile (LPAN) as the carbon source. The structure and micro-morphology of the as-prepared Li₂MnSiO₄ and Li₂MnSiO₄/C nanocomposite were characterized by thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrochemical properties of the as-prepared Li₂MnSiO₄ and Li₂MnSiO₄/C nanocomposite were evaluated cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). The results showed that Li₂MnSiO₄/C have a good electrochemical performance and the Li₂MnSiO₄ coated with a calcined 10 wt% LPAN carbon membrane insitu reached 225.6 mAh g^-1 at room temperature. It is more than one electron (1.36Li⁺) transfer during the intercalation/deintercalation process, corresponding to 68% of its theoretical two-electron redox capacity (330 mAh g^-1).