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

Low‐rate dynamic contact angles of 13 liquids on a polystyrene polymer are measured by an automated axisymmetric drop shape analysis – profile (ADSA‐P). It is found that 7 liquids yielded non‐constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the other 6 liquids, it is found that the liquid‐vapor surface tension times cosine of the contact angle changes smoothly with the liquid‐vapor surface tension, i.e. γlvcosθ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non‐inert (polar and non‐polar) surfaces (7–13, 24–26). The solid‐vapor surface tension calculated from the equation‐of‐state approach for solid‐liquid interfacial tensions (33) is found to be 29.8 mJ/m2, with a 95% confidence limit of ±0.5 mJ/m2 from the experimental contact angles of 6 liquids.