CHARACTERIZATION OF POLYSTYRENE SURFACE BY A MODIFIED 2-LIQUID LASER CONTACT-ANGLE GONIOMETRY

It is recognized that the non-dispersive components, gamma(ab), of the surface free energies, gamma, play an important role in the interactions of a polymer with other substrates. Because of the difficulty in measuring the surface free energy of a solid polymer surface, many methods to estimate gamma have been developed. The purpose here is to examine how to characterize a high energy polymer surface using our recently proposed model and the modified two-liquid contact angle technique. First, the dispersion component, gamma(d), of surface free energy of polystyrene (PS) is obtained by measuring the contact angles of water on PS surface in a series of n-alkanes. Its gamma(ab) is then calculated by our three-parameter semi-empirical model using the contact angle data of several key non-alkane liquids on the surface. Given the surface thermodynamic parameters, our model also enables us to calculate the interfacial free energies, gamma(SL), between PS and other liquids. An attempt to relate gamma(SL) to the equilibrium concentrations of crazing solvents in PS is presented.