Phase transitions between partial wetting states in the Landau theory and the Van der Waals theory of adsorbed fluids

Abstract

Adsorption phase transitions between distinct partial wetting states (or 'thin-thick' transitions at bulk two-phase coexistence) are studied systematically in the phenomenological Landau theory for Ising models, as well as in the Sullivan model, a more microscopic Van der Waals theory for fluids. In the Landau theory the previously proposed mechanism of competing surface fields is examined in detail and confirmed. In the generalized Sullivan model with combined exponential and square-well wall-fluid potentials thin-thick transitions are found already if the potential is purely square-well. A mapping of the Van der Waals to the Landau theory suggests that the mechanism of competing surface fields can largely explain the new phase transitions.