Domain complexions in capillary condensation. Part 1.—The ascending boundary curve

Abstract

A statement of the general principles of capillary condensation in porous networks and the ascertainment of its particularities for a given structure are difficult, since either independent or dependent vapour–liquid transitions arise at each point of the network and also because porous materials occurring in nature and in industrial processes possess extremely variable morphologies. However, the following stages enable one to achieve these objectives readily: (i) development of general expressions for the probability that the various elements fill with capillary condensate, according to their type (sites or bonds) and size, (ii) classification of all possible morphologies of porous structures into a few unambiguous types and (iii) for each of these types, simplification of the general expressions to obtain particular equations allowing a straightforward derivation of domain complexions and ascending boundary curves. It appears that, even if in one structural type, the less frequently encountered domains behave as though independent, for the other types, corresponding to most materials, an interdependence must be taken into account. As an extreme case of domain interactivity (also pertaining to structures represented fully, once a certain degree of filling is reached, a phenomenon arises in which the whole configuration of capillary condensate becomes unstable, the entire network then being filled.