ON THE THERMODYNAMICS OF SURFACE TRANSITIONS CLOSE TO THE BULK CRITICAL-POINT

In the Ginzburg‐Landau functional approximation, thermodynamics of phase transitions occuring at the surface of binary alloys, ferromagnets, and similar systems are analysed in detail, including finite bulk and surface thermodynamic fields. Equations describing the lines of the Nakanishi and Fisher surface transition diagram are derived. For all the lines and (multi‐)critical points of the diagram, complete sets of thermodynamic critical exponents are obtained and scaling properties of the free energy surface excess, δfs, are examined in detail. The classical scaling of the bulk only holds at the critical prewetting lines. At the rest of the transitions, δfs is either a sum of two scaling functions with different exponents or includes a logarithmic singularity in addition to the leading one. This kind of scaling apparently represents some general properties of systems with surface‐broken symmetry or in contact with a short‐range substrate. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA