from adsorption or retention data (2), and it provides infor-Adsorption isotherms of n-octane, benzene, toluene, and chloromation on the number of adsorption sites of particular interform were determined by a gas chromatographic method on the action energy. On the other hand, the surface processes result surface of silica gel heated at 200, 400, and 800ЊC. From the from various types of intermolecular interactions (3); hence, isotherms, the film pressure of the adsorbates was determined, and qualitative analysis has to be given more detailed considerthen the components of silica surface free energy were calculated.
ation. This may be achieved by the determination of the It was determined that the thermal treatment provided almost no components of surface free energy. Depending on the aschanges in nonspecific interactions and a considerable decrease in acid-base ones; however, electron-acceptor interactions were sumed theoretical approach to the problem, the total value always stronger than electron-donor ones. Based on these data, of the surface free energy is the sum of two components: the surface concentration of adsorption sites was estimated. The either the dispersion (g d S ) and the polar (g p S ) or the Lifshitzadsorption energy distribution function (x) was also determined van der Waals (g LW S ) and the acid-base (g AB S ). The disperfor silica gels according to the asymptotically corrected condensasion component results only from dispersive interactions tion approximation method. The influence of the thermal treat-(London effect), while the polar one reflects all types of ment on distribution of adsorption sites was demonstrated for interactions other than dispersive (4-6). The Lifshitz-van adsorbates possessing various types of interactions. ᭧ 1998 Academic der Waals component involves all so-called van der Waals Press interactions, while the acid-base one is determined by