Wetting of Silica by n-Alkanes

Abstract

The thicknesses of a series of n-alkane liquid films on the surface of vitreous silica were measured at a low disjoining pressure using ellipsometry. Whereas pentane, hexane and heptane wet the silica and formed thick films (∼20 nm), octane and the higher alkanes gave much thinner (<3 nm) films and formed very small but non-zero contact angles which were measured by interference microscopy. These observations were interpreted by applying the Lifshitz theory of van der Waals forces to various surface layer models. Fairly good agreement with the experimental results was obtained by using a two layer model representing a silica surface with a microporous structure impervious to the hydrocarbons.