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Viologen-based ionic liquids can form various microscopic structures at different temperatures. In this work, the dynamics of dimethyl-viologen bis-(tetrafluoroborate) ([VIO 2+ ][Tf 2 N - ] 2 ) ionic liquid within 400-800 K has been exploited by molecular dynamics simulations. [VIO 2+ ][Tf 2 N - ] 2 exhibits a supercooled liquid analogous diffusion and structural relaxation even at temperature T = 400 K, and behaves more like simple liquids as temperature increases. The variation of the diffusion constant and structural relaxation time with temperature follows a super-Arrhenius law; both can be fitted by two Arrhenius laws with a crossover temperature or fitted by a VFT law. [VIO 2+ ][Tf 2 N - ] 2 behaves as a fragile glass former. The decoupling of diffusion and relaxation is observed in [VIO 2+ ] but not in [Tf 2 N - ]. The variation of dynamics with temperature is attributed to the time differences of the persistence in ion cage and exchange out of ion cage.

Graphene nanosheets have been synthesized from commercial expandable graphite by heating in a microwave oven and dispersing in ethanol by ultrasonication. Scanning and transmission electron microscopy and electron energy-loss spectroscopy and atomic force microscope showed that the nanosheets were about 2 nm in thickness and 10 microm in diameter. The field emission of the graphene sheets has been investigated. An emission current density of 1 mA/cm2 has been achieved at an electric field of 3.7 V/microm with a turn-on field of 1.7 V/microm at 0.01 mA/cm2. The annealing of the samples at 400 degrees C in vacuum greatly improved the field emission performance.