Stabilization of Graphene Sheets by a Structured Benzene/Hexafluorobenzene Mixed Solvent

Applications requiring pristine graphene derived from graphite demand a solution stabilization method that utilizes an easily removable media. Using a combination of molecular dynamics simulations and experimental techniques, we investigate the solublization/suspension of pristine graphene sheets by an equimolar mixture of benzene and hexafluorobenzene (C6H6/C6F6) that is known to form an ordered structure solidifying at 23.7 degrees C. Our simulations show that the graphene surface templates the self-assembly of the mixture into periodic layers extending up to 30 A from both sides of the graphene sheet. The solvent structuring is driven by quadrupolar interactions and consists of stacks of alternating C6H6/C6F6 molecules rising from the surface of the graphene. These stacks result in density oscillations with a period of about 3.4 angstrom. The high affinity of the 1:1 C6H6/C6F6 mixture with graphene is consistent with observed hysteresis in Wilhelmy plate measurements using highly ordered pyrolytic graphite (HOPG). AFM, SEM, and TEM techniques verify the state of the suspended material after sonication. As an example of the utility of this mixture, graphene suspensions are freeze-dried at room temperature to produce a sponge-like morphology that reflects the structure of the graphene sheets in solution.