LOW-RATE DYNAMIC AND STATIC CONTACT ANGLES AND THE DETERMINATION OF SOLID-SURFACE TENSIONS

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 a xisymmetric drop shape analysis-profile. It was found that low-rate dy namic contact angles are essentially independent of the velocity of th e three-phase contact line and identical to the static advancing angle s. The mean contact angles for each liquid were determined by averagin g the contact angles at 10 different advancing rates. These angles wer e used to test different contact angle approaches for solid surface te nsions. It was found that these experimental contact angles on the ine rt solid surface are consistent with the equation of state approach fo r interfacial tensions. The Fowkes and the Lifshitz-van der Waals/acid -base approaches were shown to contradict experimental contact angles.