Non-covalently modified graphene sheets by imidazolium ionic liquids for multifunctional polymer nanocomposites

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Abstract

Chemical reduction of graphite oxide (GO) to produce graphene nanosheets often results in irreversible agglomeration and precipitation. Herein, stable well-dispersed graphene sheets in solvents were obtained by simultaneous functionalization and reduction of GO under alkaline conditions, in the presence of sodium borohydride and imidazolium ionic liquids (Imi-ILs) containing two vinyl-benzyl groups. In this case, positively charged imidazolium groups of Imi-ILs underwent ion-exchange with negatively charged GO sheets and were linked to their edges, while Imi-ILs were non-covalently attached onto the large surfaces of graphene through π–π and/or cation–π stacking interactions. The vinyl-benzyl reactive sites were then copolymerized in situ with methyl methacrylate to fabricate graphene/poly(methyl methacrylate) (PMMA) composites. Functionalized graphene sheets were uniformly dispersed in the PMMA matrix and contributed to large increases in storage modulus (+58.3%) and glass transition temperature (+19.2 °C) at 2.08 vol.% loading. High electrical conductivity was also achieved at graphene loading levels beyond 1 vol.% (ca. 2.55 Sm−1) with a low percolation threshold (0.25 vol.%) for the composites. Hence, a general methodology which facilitates the development of a multifunctional advanced material has been successfully established. This can be extended to other vinyl polymer-based composites containing graphene.

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