THE RELATION BETWEEN MACROSCOPIC QUANTITIES AND THE SOLID-FLUID INTERFACIAL STRUCTURE

The relation between thermodynamic quantities and the interfacial structure is described on the basis of a layer model (or an inhomogeneous cell model). By introducing the surface characteristic scaling factor C(l)* (or C(l)0) and the surface concentration (or density) distribution constant K(l), thermodynamic quantities of the interfacial phase are correlated with the corresponding quantities of the bulk phase. Relevant expressions are derived from basic principles of statistic thermodynamics. In order to clarify the relevant consequences, two systems, the hard-sphere-hard-wall system and the crystal-solution system of aliphatic compounds, are discussed. It is shown that within the framework of our model, experimental data are explained in a satisfactory way. The character of solid-fluid interfaces is discussed, in terms of wetting conditions. As a consequence of this approach, solid-fluid interfaces are classified into three typical cases: the equivalent wetting case (C(l)* or C(l)0 = 1), the more than equivalent wetting case (C* or C(l)0 < 1 ), and the less than equivalent wetting case (C(l)* or C(l)0 > 1). It turns out that except the equivalent wetting case, the concentration of solute (or the density of fluid units) in the interfacial phase will differ from that in the bulk fluid phase at equilibrium.