ABSTRACT

It is well known that both permanent and temporary dipoles give rise to three kinds of interactions, usually named van der Waals forces: dipole/dipole (Keesom), dipole/induced dipole (Debye), and dispersion (London) forces. According to relatively recent achievements [3-7], only dispersion forces are reputed to be relevant in condensed matter, because of the rather large number of nearest neighbours which yield conflicting local fields and strongly reduce the mean dipole interactions. This means that, except for the case of dilute gases, ‘polar’ interactions involving permanent dipoles can typically be neglected, although it has long been assumed that non-dispersive forces between condensed phases should be ascribed to ‘polar’ interactions, and the role of the ‘polar’ component has been frequently invoked to account for several different interfacial phenomena. Nevertheless, it is also known that the water wettability of apolar polymers, such as polyolefins, greatly increases if chemical functions endowed with polar bonds are introduced by appropriate surface treatements. Since polar contributions cannot be responsible for any significant enhancement of interfacial actions, such a behaviour requires a quite different explanation of the forces involved. The currently accepted answer is acid-base interactions and, specifically, the particular sub-set of Lewis acid-base interactions known as hydrogen bonding [6, 7], The fundamental role of acid-base interactions in the interfacial behaviour of condensed phases is now largely recognized and it has led to a large amount of work on this subject, particularly in the last 10 years or so [3-6, 8].