ABSTRACT
Virtually all the interfacial interaction energies occurring in liquids contain the interfacial tensions between condensed-phase molecules and those of the liquid, either as the sole term, or as one or several of the terms in one of the mathematical expressions for these molecules’ free energies of interfacial interaction with or in the liquid, as exemplifi ed by one or another version of the Dupré equation (see also the footnote thereto), such as eq. II-36, which pertains to the interfacial (IF) free energy of interaction (ΔGIF12) between two different condensed-phase materials, 1 and 2 in air or in vacuo, but which for compounds or materials, i, immersed in water, w, alludes to the interfacial free energy of hydration (ΔGIFiw). The simplest version of the Dupré equation (see eq. II-33A) shows the proportionality between γ12 and the interfacial free energy of cohesion of molecules, 1, immersed in a liquid, 2, i.e., ΔGIF121, which when liquid, 2, is water, is expressed as ΔG wLW1 1. The latter is also the expression which quantitatively defi nes the degree of hydrophobicity (when ΔG wLW1 1 < 0) or hydrophilicity (when ΔG wLW1 1 > 0), of compound or material, 1; see also van Oss and Giese (1995) and Chapter XIX. Finally, eq. II-37 expresses the interfacial free energy of interaction between two different condensed-phase materials, 1 and 2, immersed in liquid, 3, where ΔGIF132 is a function of all three pertinent interfacial tensions, γ12, γ13 and γ23. All the above equations for various forms of ΔGIF, quoted from Chapter II, have LW as superscript in that Chapter, as it deals with LW interactions, but these equations are equally valid with superscript AB and, as used in the present Chapter, with superscript IF, where ΔGIF = ΔGLW + ΔGAB, cf. eq. IV-1.
