Structure, Chemistry and Energy of Carbon Surfaces

In this paper, the graphene layer is considered as the basic structural unit in a range of carbon materials. The effects of 2D and 3D order in defining the microstructures and macrostructures of carbons are reviewed along with the related concept of graphene layer orientation within the structure and the resulting ratio of basal plane to edge site as well as its effects on surface chemical reactivity and energy. Both non-specific and specific surface forces and the resulting potentials are considered. Theoretical physical models based on the Lennard-Jones potential applied to the basic structural units, either as an ideal, i.e. perfect, single graphene layer or as multiple layers of varied inter-layer spacing and size, are presented. Mention is then made of non-ideal surfaces (stepped or containing vacancies) and their resulting enhanced potential. The effects of incorporating chemical heterogeneity into the surfaces of these structures are also considered: carbon oxidation mechanisms are discussed in terms of bond energy and disruption of (conjugated) graphene structure and the resulting polar functional groups are shown to increase interactivity with molecules that possess permanent dipoles or multipoles. The resulting increases in the polar component of surface-free energy can be used to control properties of adhesion, adsorption and wettability.