Study On Garphene Preparation And Graphene-based Conductive Nanocomposite Membranes

Graphene ,which was first reported in 2004,has attracted tremendous attention from both the method of preparation and its application in recent years.In this paper we prepared graphene and graphene/Poly(vinylidene fluoride)(PVDF) conductive nanocomposites.Then we applied the alternating current during the process of preparation,and the influence of the electric field on the membrane's performance was explored.Graphene oxide was prepared by using a modified Hummers method.Then we used hydrazine for chemical reduction of graphene oxide to graphene. Results showed graphene has the thin paper-like wrinkled sheets remaining somewhat interconnected with one another. Graphene oxide has abundant epoxide,hydroxyl and carboxyls groups.This makes it hydrophilic and has a good dispersion in many solvents.After the reaction,however,graphene showed a significant reduction in the amount of the functional groups present.It is insoluble and agglomerates together in water.The diffraction intensity of graphene is much weaker than that of graphite and graphene oxide.We thought that geaphene was exfoliated to monolayer or a few layers,thus formed a new lattice structure.Graphene has better thermal stability than graphene oxide and the weight loss is just eighteen percentage when temperature reaches 800℃.Graphene/PVDF nanocomposites were prepared by a solution mixing method for the first time. Meanwhile we applied the alternating current during the process of preparation. Also we prepared graphite/PVDF composites for comparation. SEM images of fractured surfaces show a winkled topography for the graphene based composites. The electrical conductivity of nanocomposites increases with more loading of graphene. Graphene/PVDF nanocomposites show low the percolation threshold around 1wt% graphene loading. These nanocomposites has good electrical conduction. The in-plane conductivity is 0.034s/cm,and vertical conductivity is 0.85e-4 s/cm when graphene loading is 5wt%.But graphite/PVDF composites don't have much obvious effect in electrical conduction.Incorporation of graphene leads to improve the crystallization of PVDF. The tensile strength of the graphene/PVDF membranes firstly increases and then decreases with dopping more and more graphene. The biggest tensile strength of membranes ,which is 39MPa when graphene loading is 0.5wt%, improves by 23.2 percentage than pure PVDF membrane. Results showed that the electric field can induce the graphene to orient along the electric field direction, thus improving obviously the conductivity of blend membranes in the thickness direction,consequently the in-plane conductivity decreases. The diffraction intensity of PVDF in 20.1°is stronger than pure PVDF membrane. Graphene increases the elongation at break and the tensile strength of the PVA membrane. The tensile strength increases by 20.12% and the the elongation at break increases by 33.3% than pure PVDF membrane when graphene loading is 1wt%.