LOW-RATE DYNAMIC CONTACT ANGLES ON POLY(METHYL METHACRYLATE) AND THE DETERMINATION OF SOLID-SURFACE TENSIONS

Low-rate dynamic contact angles of nine liquids on a poly(methyl metha crylate) (PMMA) polymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that two liquids dissolv ed the polymer on contact. From the experimental contact angles of the other seven polar and nonpolar liquids, it is found that the liquid-v apor surface tension times cosine of the contact angle changes smoothl y with the liquid-vapor surface tension (i.e., gamma(l nu) cos theta d epends only on gamma(l nu) for a given solid surface). The dependence of gamma(l nu) cos theta on gamma(s nu) is explicitly illustrated by r eplacing the solid surface from the PMMA to other methacrylate polymer s: such a procedure shifts the curves in a very regular manner. Thus, because of Young's equation, gamma(sl) depends only on gamma(l nu) and gamma(s nu). This contact angle pattern is in harmony with those from other inert and noninert (polar and nonpolar) surfaces. The solid-vap or surface tension of PMMA calculated from the equation of state appro ach for solid-liquid interfacial tensions is found to be 38.5 mJ/m(2), with a 95% confidence limit of +/-0.5 mJ/m(2) from the experimental c ontact angles of the seven liquids. (C) 1998 Academic Press.