A critical evaluation of the binary and ternary solid–oil–water and solid–water–oil interaction

When determining the surface energies of solids the most frequently utilised method is to measure contact angles for particular probe liquids. The measured contact angles (usually measured in air) are then combined with published values of surface- and interfacial tensions of the liquids to give the surface energy of the solid. It is, however, very seldom that sufficient attention is paid to the impurities, to the experimental (e.g. saturated vapour) conditions chosen and to the heterogeneities (chemical and structural) of the solid surface. In this study five typical probe liquids: octane, hexadecane, diiodomethane, α-bromonaphthalene and water have been used to establish the dispersion component of the surface energy of the solid and the hydrophobic interaction occurring at the interface of four solids: hydrophobic/hydrophilic SiO2 and hydrophobic/hydrophilic TiO2. Two (solid/liquid) and three (solid/liquid/liquid) component systems were investigated. The results are compared with previously published results when Alkenyl Succinic Anhydride (ASA) was brought into contact with SiO2 under water. The preferential surface vapour pressure and liquid spreading of the one liquid over the solids in the absence and presence of a saturated liquid vapour were evaluated as sources of errors.