Ethylene/ ammonia plasma polymer deposition for controlled adhesion of graphite fibers to PEEK

Plasma polymerization of ethylene and ammonia gas mixtures is used to obtain uniform polymer coatings on the surface of AS4 graphite fibers. The polymer deposition rates were determined for processing parameters such as composition of the monomer mix, monomer flow rate, chamber pressure, and power input of the radio frequency field. Plasma formed polymers were characterized using Fourier Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS). XPS spectra were collected at 75° and 30° takeoff angles to obtain elemental composition and functional group populations at different sampling depths. Plasma deposition rate was the smallest for 100% ethylene and increased by three to four fold when ammonia was added to the monomer mixture. The polymer coatings were of uniform thickness and exhibited a complex crosslinked structure. The 100% ethylene plasma polymer was strongly hydrocarbon in nature but had some oxygen and nitrogen containing groups. Plasma polymers from ethylene/ammonia mixture were much more polar and contained reactive and polar group constituents, including carbonyl, ether, primary and secondary amines, and hydroxyl groups. The presence of oxygen and nitrogen functionalities is presumed to arise primarily from the reaction of trapped radicals with oxygen and nitrogen when exposed to air. Small amounts of silicon were also detected in the plasma formed films.