Low-rate dynamic and static contact angles and the determination of solid surface tensions

Abstract

Low-rate dynamic contact angles of 17 liquids on a carefully prepared solid surface (FC-722 dip-coated on a mica surface) were measured by axisymmetric drop shape analysis-profile. It was found that low-rate dynamic contact angles are essentially independent of the velocity of the three-phase contact line and identical to the static advancing angles. The mean contact angles for each liquid were determined by averaging the contact angles at 10 different advancing rates. These angles were used to test different contact angle approaches for solid surface tensions. It was found that these experimental contact angles on the inert solid surface are consistent with the equation of state approach for interfacial tensions. The Fowkes and the Lifshitz-van der Waals/acid-base approaches were shown to contradict experimental contact angles.