No violations of critical-point wetting in ternary three fluid-phase systems with short range interactions

Summary

Hypothesis: In ternary three-fluid phase systems one can have either three- or just two interfaces. In a wetting transition the system switches from partial to complete wetting, i.e., from having three- to two interfaces. The system can also undergo a bulk phase transition when the number of bulk phases changes from three to two. Upon varying the temperature one will find that first the system switches from having three interfaces to two, before it changes from having three phases to two. This order of events is predicted by Cahn. SCF computations: We use a quasi-off lattice variant of the Scheutjens Fleer self-consistent field theory, which implements a mean field approximation with short-range interactions parameterised by Flory-Huggins interaction parameters, to generate a set of wetting phase diagrams for this system. There exists special coordinates such that each wetting phase diagrams has a power-law wetting transition line. Findings: Overlooking the full set of wetting phase diagrams, it is concluded that no exceptions to the Cahn rule exists unless the system is exactly (ideally) molecularly symmetric, sometimes called ‘the neutral value’ where the contact angle remains 90^∘ up to the bulk critical point. Importantly, all wetting transitions may be induced similarly, that is they all can be classified and understood from Cahn's perspective.