Description of the thickness of the adsorbed layer, identification of the instability characteristics of the liquid–vapour interface and assessment of criticality in elliptical pores through the Broekhoff de Boer theory

This paper analyses the growth of the adsorbed layer during the course of N adsorption verified in two types of elliptical pores, oblates and prolates, by means of the Broekhoff de Boer theory. The information provided by the value of the thickness of the adsorbed layer permits to characterize the geometrical features of the liquid–vapour interface at every stage of the isotherm, prior and at the onset of capillary condensation. The features of the liquid–vapour interface that are characteristic of the instability at the onset of capillary condensation were identified. Additionally, the critical ellipsoidal pore sizes were calculated, thus identifying the limit of stability for the formation of the liquid–vapour interface during N adsorption.