Molecular Resolution in situ Imaging of Spontaneous Graphene Exfoliation

All reported methods of graphene exfoliation require external energy input, most commonly from sonication,(1) shaking,(2) or stirring.(3) The reverse process-aggregation of single or few layer graphene sheets-occurs spontaneously in most solvents. This makes producing, and especially storing, graphene in economic quantities challenging,(4'5) which is a significant barrier to widespread commercialization. This study reveals ionic liquids (ILs) can spontaneously exfoliate graphene from graphite at room temperature. The process is thermally activated and follows an Arrhenius-type behavior, resulting in thermodynamically stable IL/graphene suspensions. Using atomic force microscopy, the kinetics of the exfoliation could be followed in situ and with subnanometer resolution, showing that both the size and the charge of the constituent IL ions play a key role. Our results provide a general molecular mechanism underpinning spontaneous graphene exfoliation at room temperature in electrically conducting ILs, paving the way for their adoption in graphene-based technology.