Sum rule analysis of continuous wetting phenomena

Abstract

Exact sum rules are derived for a general fluid in the presence of a one-body external field. This enables an interpretation of continuous wetting behaviour within the context of rigorous many-body theory. We discuss both the case of an approach to complete wetting from off bulk two-phase coexistence and examples of continuous wetting transitions at bulk two-phase coexistence (critical wetting). In particular, universal exponent relations are obtained from the sum rules, with solutions that follow from general considerations of interfacial pair-correlations. Difficulties with interpretation arise only for the case of critical wetting in the absence of effects from power-law external fields.