MOLECULAR-STRUCTURE OF INTERFACES BETWEEN PLASMA-POLYMERIZED ACETYLENE FILMS AND STEEL SUBSTRATES

Plasma-polymerized films of acetylene were deposited onto steel substr ates in an inductively coupled reactor by exciting the plasma in an ar gon carrier gas and then injecting the monomer into the afterglow regi on. The molecular structure of the film/substrate interface was determ ined using reflection-absorption infrared spectroscopy (RAIR) and X-ra y photoelectron spectroscopy (XPS) to characterize the films as a func tion of thickness. RAIR showed that thick (similar to 900 Angstrom) as -deposited plasma-polymerized acetylene films had a complicated molecu lar structure and contained methyl and methylene, mono- and disubstitu ted acetylene, vinyl, and cis- and trans-disubstituted olefin groups. Evidence of oxidation resulting from the reaction of trapped radicals with atmospheric oxygen and moisture to form O-H and C=O groups was al so obtained. The molecular structure of thin films (similar to 60 Angs trom) was similar although evidence was obtained to indicate that acet ylide groups (H-C=C-) were present at the film/substrate interface. Re sults obtained using angle-resolved XPS analysis showed that carbonace ous contamination was removed from the substrate and that oxides and h ydroxides on the substrate surface, especially FeOOH, were chemically reduced during deposition of the films. XPS also confirmed that plasma -polymerized acetylene films deposited on steel substrates contained d rop C-O- and drop C=O groups. Preliminary results also showed that fil ms deposited in an inductively coupled reactor were good primers for r ubber-to-metal bonding, whereas films deposited in a capacitively coup led reactor were not. The differences may be due to the wide variety o f functional groups found in the former type of films but not in the l atter. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1283-1298 , 1998.