Adsorption of n-octane and n-propanol on the graphite surface precoated with n-hexadecane

Abstract

Adsorption isotherms of n-octane and n-propanol were determined at different temperatures on a bare graphite surface and on the surface precoated with various amounts of n-hexadecane. From these isotherms the isosteric heat of adsorption and the differential molar entropy of adsorption were calculated. Additionally, the term πS kT (resulting from the simplest two-dimensional equation of state) was determined. The obtained results were discussed in terms of the structure of adsorbed layers as well as in terms of previously calculated components of surface free energy. It was stated that film pressure of n-octane might be equated to the work of spreading wetting of liquid n-octane on both bare and precoated graphite surfaces. The mechanism of n-propanol adsorption onto a graphite surface appeared quite different from that of n-octane. From the proposed structure of the n-propanol layer adsorbed on the graphite surface (precoated with hexadecane) it appeared that the film pressure of n-propanol did not achieve the value corresponding to the work of spreading wetting of liquid adsorbate on the surface.