DISJOINING PRESSURE OF POLYMOLECULAR ADSORPTION FILMS OF APOLAR SUBSTANCES AT GRAPHITIZED CARBON-BLACK

The known published data on the polymolecular adsorption of nitrogen, methane, hexane, and benzene on graphitized carbon black are considere d. The dependence of the disjoining pressure on the thickness of adsor ption layers in the systems investigated was shown to deviate signific antly from the theory of dispersion forces. Based on IR and UV spectra as well as on the approximation formulas characterizing absorption pr operties of graphite, the Hamaker constants for the interaction of ads orbate molecules with an adsorbent were calculated. It was shown that the differences between experimental and theoretical results can be as sociated with two reasons. The first one is attributed to the fact tha t the position of the plane of maximal approach of adsorbate molecules to the adsorbent surface is not accounted for during the calculation of the molecular component of disjoining pressure. The second reason c an be related to the effect of structural forces caused by variations in the structure of Liquid in thin layers. The processing of the disjo ining pressure isotherm plotted by the data on adsorption measurements enables us to determine the Hamaker constants and the localization of the adsorption plane and to calculate parameters characterizing the s tructural component of disjoining pressure. It was established that th eoretical and experimental results are well consistent with each other both by the orders of magnitude and the regularities of their variati ons. However, the analysis performed does not allow us to draw an unam biguous conclusion about the reasons for the deviations of the disjoin ing pressure of polymolecular adsorption films of apolar Liquids on po lar adsorbents from the theory of molecular forces.