Molecular Dynamics Studies of Graphite Exfoliation Using Supercritical CO₂

Abstract

Molecular dynamics simulations are used to investigate the microscopic mechanisms of graphite exfoliation using CO₂ at supercritical conditions. Two approaches are used: simulations in the canonical ensemble are done by keeping the atoms in the graphite structure fixed but increasing the interlayer separations above their normal value. This procedure allows us to determine the interlayer separation at which the CO₂ molecules may be able to intercalate graphite at near and supercritical pressures and temperatures, and to evaluate self-diffusion coefficients at those conditions. In the second approach, the isothermal-isobaric ensemble is utilized allowing graphite to relax, to observe how the exfoliation process may take place at the various pressures and temperatures near and above the CO₂ critical point. Analyses of the simulation trajectories reveal that the exfoliation process takes place at increasing rates as the pressure increases at constant temperature, with intercalation of CO₂ molecules causing bending and then separation of graphene layers.