Preparation and properties of plasma-deposited films with surface energies varying over a wide range

Abstract

Polymer surfaces have been modified by chemical reaction or thin film deposition using a capacitatively coupled plasma RF-discharge system. This has allowed the production of a graded, reproducible series of surfaces with surface energies ranging from low to high. Three gases, hexafluoroethane (C2F6), perfluoropropane (C3F8), and hexafluoropropene (CF3CFCF2), were used to prepare the low-energy surfaces. Ethylene oxide (C2H4O) was used to prepare the higher energy surfaces. Intermediate values of surface energy were obtained by using gas mixtures of perfluoropropane and ethylene oxide. The plasma-deposited films were characterized by ESCA and contact-angle studies. In the low-energy range, the critical surface tension (γc) values of the films prepared were found to be lower than those for Teflon. For the higher energy surfaces, values up to about 45 dyn/cm were obtained. Addition of oxygen to the plasma permitted the production of films with still higher γc values. ESCA studies indicate that, under the reaction conditions used, C3F8 and CF3CFCF2 form a fluoropolymer deposit on glass that is at least 100 Å thick. For the same reaction parameters, C2F6 resulted in more etching and deposition of a much thinner film.