The critical behavior at complete wetting can be understood in the framework of effective interface models [5] [1]. Depending on the direct molecular interactions between the two interfaces, these transitions exhibit two different scaling regimes: In the fluctuation regime, the transitions are controlled by the fluctuation-induced interactions arising from the hard wall constraint; in the other regime, the transitions are governed by the molecular interactions. [2]. The same distinction applies to systems with quenched disorder [6] [7] and quasi-periodic order [8].
A particularly subtle case is provided by 3-dimensional systems with short-ranged molecular interactions that decay exponentially with the interfacial separation. In this case, the two regimes can be obtained by a non-perturbative treatment of the hard wall interaction [9] [10] as confirmed by Monte Carlo simulations [10]. The two regimes also differ in the critical behavior of the contact probability for the two interfaces [10].