Résumé
The energetics of capillary condensation processes in two systems has been studied. In the first system, namely n-hexane/MCM-41, the adsorbate/adsorbent interaction is known to be very weak, and the adsorption isotherms obtained at various temperatures all exhibit Henry's law type behaviours at relative pressures up to capillary condensation. The second system is the system 1-hexene/MCM-41 in which adsorbate/adsorbent interactions are more important, as evidenced by the clear knees on the adsorption isotherms. These findings have been confirmed by the determination of the differential isosteric enthalpy of adsorption at zero coverage. When focusing on the capillary condensation process, (0.3–0.7 in fraction of pore filling) dramatic enthalpic excesses are exhibited as compared to the enthalpy of condensation in the bulk, and this excess is inversely proportional to the pore size of the porous materials. The enthalpic contribution of the liquid/gas interface to the overall process has been derived, by using a scaling effect approach, and in the case of the system n-hexane/MCM-41, exactly matches the difference between the enthalpy of condensation in the bulk and the enthalpy condensation in mesopores as large as 10nm. In the case of the system 1-hexene/MCM-41, strong deviations have been observed due to intermolecular interaction.