Plasma-polymerized organic coatings deposited on metals from a DC plasma. Characterization and corrosion performance of such surface modifications

Thin films of plasma-polymerized dimethylsilane and hexamethyldisiloxane were deposited on cold-rolled and stainless steel substrates using a custom-built DC parallel plate reactor. The metal substrates were pretreated in plasmas of hydrogen, argon, and oxygen. The films were characterized by time-of-flight secondary ion mass spectrometry (TOFSIMS), reflection-absorption infrared spectroscopy (RAIR), scanning tunneling microscopy (STM), electrochemical impedance spectroscopy (EIS), and surface energy measurements. The objective of this research project was the development of alternative metal pretreatments that can replace currently used chromate and phosphate systems without sacrificing the metal's corrosion resistance after painting with automotive paint systems. Some characteristics of the DC plasma deposition process were studied, such as the effect of deposition time, pressure, flow rate and discharge power. Attempts to improve the performance of the films further by etching the plasma-polymerized film with an oxygen plasma were unsuccessful. STM demonstrated that such treatments modified the surface morphology of the films. RAIR showed that the entire film composition had changed in the etching process. EIS was shown to be a powerful technique for studying the stability of the paint-metal interface modified by a plasma-polymerized film.