Study of the surface properties of exfoliated highly oriented pyrolytic graphite (HOPG) by means of captive bubble and sessile drop contact angle measurements
Surface thermo-dynamics of graphite play an important role in surface physical and chemistry in particular for graphene, in the chemical industry, battery technology and nano-confined liquids applications. Literature is mainly focused on the study of water-graphite or water-graphene interaction, and few papers reported the surface tension (SFE) and the interaction of graphite with other solvents such as alcohols, oils, solutions or gases. In this work, the interaction of HOPG graphite with liquids and gases was studied (a) by means of sessile contact angle measurements and (b) using the captive bubble method. Fresh surfaces of graphite were prepared by scotch- tape exfoliation of pure highly oriented graphite (HOPG). The chemistry and morphology properties were studied using X-ray photoemission spectroscopy (XPS) and atomic force microscopy (AFM). By using probe liquids, we determined the surface free energy following different methods such as Zisman plot, Owens Wendt method, Van Oss et al. approach and Neumann equation. HOPG surface showed a good interaction with liquids, which present dispersive behavior like liquid paraffin and di-iodomethane. The total surface energy was 45mJ/m2 and the main component of SFE was due to Liftshits –Van der Waals interactions. Gasses (Ar, N2, air, He and H2) showed a weak interaction with HOPG and the interaction appeared to be tailored by polarizability of the gasses.