Influence of the argon ratio on the structure and properties of thin films prepared using PECVD in TMSAc/Ar mixtures

Capacitively coupled RF glow discharge was used to form novel coatings of SiOxCyHz using varying proportions of trimethylsilyl acetate (TMSAc) monomer and the carrier gas argon. The properties of the TMSAc-based plasma polymers produced depend significantly on the proportion of argon in TMSAc/Ar gaseous mixture, which ranged from 0 % to 75 %. Reaction mixtures containing less than 50 % Ar produced hydrophobic polymers, for which the indentation hardness values were less than 1.5 GPa. Seventy-five percent argon in the reaction mixture yielded a crosslinked carbon-rich organosilicon structure with a hardness of 6 GPa. As many applications require good stability in a liquid environment, the TMSAc-based coatings were immersed in phosphate buffered saline (PBS) for 14 days. Because any material used in a medical application must be resistant to the techniques used for sterilization, the prepared coatings were subjected to a standard sterilization procedure using UVC radiation. A degree of the structural changes induced by both environments corresponded to the argon ratio used for production of thin films. Possible degradation mechanisms were examined and discussed. Using 7.7-21.4 % Ar during the deposition process led to the TMSAc-based plasma polymers exhibiting good resistance to the prolonged immersion in PBS and UVC sterilization.