ABSTRACT
Air, at the water-air interface, has the most unusual and extreme properties. It causes a zero-energy interface which can be attributed to the low density of gases, resulting in extremely weak interactions at the interface with another material (Docoslis et al., 2000). The surface tension of air (A) is zero because the Lifshitz-van der Waals or apolar component of its surface tension ( )γ ALW is zero, as well as its Lewis acidbase component ( )γ AAB , so that γ γ γATOT ALW AAB= + = 0, where 2 0γ γ γAAB A A= = , not because the interface is monopolar (as happens with many hydrophilic compounds) when γ A = 0 (van Oss, Chaudhury and Good, 1987a), but because both γ A and γ A are equal to zero.
