Differentiating Defect and Basal Plane Contributions to the Surface Energy of Graphite Using Inverse Gas Chromatography

Historically, reported values for the surface energy of graphite have covered a very wide range. Here, we use finite-dilution inverse gas chromatography (FD-IGC) to show that the dispersive component of the surface energy of graphite has contributions from edge and basal plane defects as well as from the hexagonal carbon lattice. The surface energy associated with the defect-free hexagonal lattice is measured at high probe-coverage to be 63 +/- 7 mJ/m(2), independent of graphite type. However, the surface energy measured at low probe coverage varied from 125 to 175 mJ/m(2) depending on the graphite type. Simulation of the FD-IGC output for different binding site distributions allows us to associate this low-coverage surface energy with the binding of probe molecules to high energy defect sites. Importantly, we find the rate of decay of surface energy with probe coverage to carry information about the defect density. By analyzing the dependence of these properties on flake size, it is possible to separate out the contributions of edge and basal plane defects, estimating the basal plane defect content to be similar to 10(15) m(-2) for all graphite samples. Comparison with simulation gives some insights into the basal plane and defect binding energy distributions.