  We use molecular dynamics simulation to study the exfoliation of graphene and
fluorographene in molecular and ionic liquids, by performing computer
experiments in which one layer of the 2D nanomaterial is peeled from a stack,
in vacuum and in the presence of solvent. The liquid media and the
nanomaterials are represented by fully flexible, atomistic force fields. From
these simulations we calculate the potential of mean force, or reversible work,
required to exfoliate the materials. Calculations in water and organic liquids
showed that small amides (NMP, DMF) are among the best solvents for
exfoliation, in agreement with experiment. We tested ionic liquids with
different cation and anion structures, allowing us to learn about their solvent
quality for exfoliation of the nanomaterials. First, a long alkyl side chain on
the cation is favourable for exfoliation of both graphene and fluorographene.
The presence of aromatic groups on the cation is also favourable for graphene.
No beneficial effect was found between fluorine-containing anions and
fluorographene. We also analysed the ordering of ions in the interfacial layers
with the materials. Near graphene, nonpolar groups are found but also charged
groups, whereas near fluorographene almost exclusively non-charged groups are
found, with ionic moieties segregated to second layer. Therefore,
fluorographene appears as a more hydrophobic surface, as expected.
