ABSTRACT
The molecular mechanism of the strong long-range “hydrophobic” interactions between mainly apolar macromolecules or particles immersed in aqueous media does not yet seem to be established with convincing clarity, or unanimity of pinion (Israelachvili, 1985; Claesson, 1986). Israelachvili (1985, p. 105) states that “on the theoretical side the problem is horrendously diffi cult, and there are no simple theories of the hydrophobic interaction, though a number of promising approaches have been proposed”; see also Israelachvili (1991, p. 132). Claesson (1986, p. 82) concludes that “several years of experimental and theoretical research work concerning repulsive and attractive hydration forces [must be] anticipated before a satisfactory understanding of the origin[s], properties and implications of these forces are obtained.” We showed earlier (van Oss et al., J. Colloid Interface Sci., 1986) that hydrophobic interactions arise out of a combination of Lifshitz-van der Waals forces and hydrogen bonds, where the contribution of the latter forces is the preponderant one by far. We proposed at the time that the attractive part of the term interfacial forces, or interfacial interactions, would more accurately describe hydrophobic interactions (van Oss and Good, J. dispersion Sci. Tech., 1988). It should be realized that, even tefl on or hydrocarbons strongly attract water (see also Hildebrand, 1979; Tanford, 1979 and Tanford, 1980, p.3), with a free energy ΔGiw ≈ – 40 to –50 mJ/m2. Thus the term “hydrophobic” used to characterize such materials is a misnomer. It may even be suggested that the epithet “hydrophobic” has signifi cantly retarded a more general understanding of the phenomena discussed in this chapter (see also van Oss and Good, 1991b, as well as Chapter IX, which treats hydrophobic interactions from the point of view of the properties or water).
