Enhanced electrical, mechanical and thermal properties by exfoliating graphene platelets of larger lateral dimensions

Abstract

Conventional liquid-phase graphite exfoliation (LPE) dramatically reduce the lateral dimension of graphene sheets to submicrometer levels due to bond cleavage induced by high shearing force or long processing time, resulting in highly degraded properties of graphene materials. Herein, a modified high-yielding LPE for producing graphene in the cosolvents of ethanol and water is demonstrated, via the prior use of an electrochemical expansion process on graphite. The electrochemically expanded graphite allows the use of significantly lower sonication power and shorter sonication times. Therefore graphene platelets with largely increased lateral dimension were achieved compared to conventional LPE (the size can reach up to 10 μm). The electrical and mechanical properties of graphene film are significantly enhanced as a result, with the electrical conductivity doubled and the modulus increased by a factor of 4 as well as a considerably higher areal capacitance for the assembled solid supercapacitor. Furthermore, a type of multifunctional benzoxazine surfactant was used to stabilize graphene sheets, which can also facilitate to transfer graphene sheets into organic solvents from aqueous dispersions. On this basis, polymer-graphene nano-composites have been easily prepared for both water soluble poly(vinyl alcohol) (PVA) and organic soluble poly(methyl methacrylate) (PMMA) with improved mechanical properties and thermal diffusivity.