Preparation Of Graphene/Silicone Rubber Composite By Ionic Liquid Exfoliated Expanded Graphite

As a new "green" solvent, ionic liquid owns the good properties of negligible vapour pressure, high conductivity, high thermal stablility and high chemical stability. It has been used in application for electrochemistry, catalyst, the synthesis of polymer composites and substances separation. As efficient fillers, carbon materials can improve the conductive, thermal, chemical and physical properties of polymer composites. However, Van der Waals force among carbon particles is strong, which hinders the uniform dispersion of fillers in matrix and dicreases chemistry and physics properties of composites. Carbon particles can be uniformly dispersed in composites with the aid of ionic liquid which is a good dispersant. In addition, the presence of ionic liquid will improve the character of composites. Ionic liquid modified carbon material becomes an interesting material because of their high performance and potential in different applications. These composites have been used for electrochemical and energy storage devices, catalysis and nano fillers for polymer composites. In this paper, ionic liquid was used to modify expanded graphite. Expanded graphite was successfully exfoliated into graphene with the aid of the shear force and ionic liquid. Secondly, composites were prepared by using bi-component room temperature vulcanization silicone rubber RTV as matrix and milled ionic liquid-expanded graphite as filler. XRD, SEM, TEM, TGA, megger and some other tests were carried out to study the conducitive, thermal, structural and rheological properties of the composite.Through experiments, following conclusions can be obtained:(1) Graphite oxide was subjected to thermal shock at600℃for a short time to form "worm-like" expanded graphite. After ball milling, expanded graphite was successfully exfoliated into graphene with the aid of ionic liquid. Graphene exhibited small size, curly, single and multiple layers. Through cation-π, π-π conjugation and Van der Waals’force between ionic liquid and graphene, ionic liquid was absorbed on the surface of graphene. Milled IL-EG can remain uniformly suspended in acetone solvent for a long time.(2) It can be seen that ionic liquid modified expanded graphie was uniformly dispersed in the silicone rubber composite. Ionic liquid, as a good compatibilizer, improved the interaction between graphene and silicone rubber. Therefore, glass transition temperature (Tg) of composite was increased. Based on the experiment result, it indicated that Milled IL-EG tends to form uniform interconnection network with the aid of IL. Consequently the electrical conductivity of composite was increased. The volume resistivity of composite with3wt%Milled IL-EG was significantly recuded.(3)The result showed that uniform dispersion of graphene in silicone rubber was successfully achieved with the modification of IL, it increased the viscosity of composite. The viscosity of composite with3wt%Milled IL-EG was32.24Pa·s. Flow activation energy of Milled IL-EG/SR composite was high, so composite was more sensitive to the thermal changes. The negative effect of Milled IL-EG on the vulcanization of SR was smaller in compared with Milled EG.