Surface energy and adsorption energy distribution measurements on some carbon blacks

The dispersive component of the surface energy (γ_s^d) of various carbon blacks and of nitric acid or heat-treated samples has been measured by inverse gas chromatography (IGC). It is shown that IGC, at infinite dilution, applies poorly to carbon blacks and provides only apparent and excessively high values of γ_s^d (a few hundreds of mJ/m²). IGC, at finite concentration, readily allows the obtention of n-alkanes, benzene and chloroform adsorption isotherms from which various thermodynamic values are computed (spreading pressure π, isosteric enthalpy of adsorption, surface energy characteristics). The γ_s^d values calculated from π_e are in the 80–120 mJ/m² range (i.e. values which are in fair agreement with published data on graphite or graphitized carbons). Further, the specific interaction potential of polar probes is in relation, as expected, with the oxygen content of the carbons. Finally, from the adsorption isotherms, the adsorption energy distribution function is computed, supposing a patchwise distribution of adsorption sites. The results confirm the high surface heterogeneity of carbon blacks and the influence of surface treatments, but indicate also major differences between carbon blacks from different preparation processes.