Thermally Activated Condensation and Evaporation in Cylindrical Pores

In a confined geometry, thermal activation gives rise to specific condensation or evaporation mechanisms. Accounting for this phenomenon is therefore important for characterizing porous materials from their sorption isotherms. However, most phenomenological models discussing thermal activation in strong confinement are only qualitative. Here, we use a semimacroscopic approach to compute the temperature and diameter dependences of the condensation and evaporation for a fluid confined in a cylindrical nanopore in the presence of thermal activation. In particular, our model predicts the effect of confinement on cavitation. Our results show how thermal activation controls the existence and shape of the hysteresis loop in porous materials with noninterconnected cylindrical pores, and shed a new light on the applicability of the classical Barrett–Joyner–Halenda method for determining pore diameter distributions in porous materials. This work paves the way to a phenomenological multiscale approach able to describe condensation and evaporation in materials with connected pores.