Chapter 10
Polymer Surface Modification by Dual-Frequency Plasma Treatment M. H. Bernier, J. E. Klemberg-Sapieha, L. Martinu, and M. R. Wertheimer
Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: November 9, 1990 | doi: 10.1021/bk-1990-0440.ch010
Groupe des Couches Minces and Department of Engineering Physics, École Polytechnique, C.P. 6079, Succursale A, Montreal, Quebec H3C 3A7, Canada
Several commercial polymers (polyethylene, polyimide, polytetrafluoroethylene, polyvinylchloride and polycarbonate) have been treated by low temperature glow discharge plasmas in various gases, namely NH , O , Ar, and CF . These surface modifications were performed in "pure" microwave (2.45 GHz, "single-mode") or in combined microwave/ radio frequency (2.45 GHz/13.56 MHz, "dual-frequency") plasma. Important systematic changes of the surface composition, wettability, and adhesion of thin metal films were observed for different substrate bias values, and for the different gases. The modified surface-chemical structure is correlated with contact angle hysteresis of water drops; this helps to identify which surface characteristics are connected with the wettability heterogeneity and with adhesive bonding properties, and how they are influenced by plasma-surface interactions. 3
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Over the years, several methods have been developed to modify polymer surfaces for improved adhesion, wettability, printability, dye-uptake etc. These include wet-chemical treatments, and exposure to flames, corona discharges, and glow discharge plasmas. Among these, low pressure, low temperature nonequilibrium plasma treatment has proven increasingly attractive for the treatment of polymer surfaces (1). Due to inelastic collisions of electrons (typical energies 1 - 1 0 eV) in low pressure (0.01 - 1 Torr) discharges, the plasma contains ions in the same concentration as electrons, to preserve quasineutrality, and neutral molecules, namely the original ground state parent gas molecules and also chemically reactive species such as metastable excited molecules and molecular fragments (free radicals). These particles, and photons emitted from excited species, can interact with the surfaces exposed to the plasma; depending mainly upon the type of feed gas, this can result in deposition, etching (chemical and/or ion-assisted), or modification of the surface structure and surface-chemical composition ("grafting"). A l l these can drastically 0097-6156/90Λ)440-0147$06.00Α)
