Comparative study of the aging behavior of plasma activated hexamethyldisiloxane-based plasma polymers and silicone elastomer thin films

The aging of plasma activated plasma polymer films has been studied to a limited extent, despite the recent application-oriented interest for these coatings. Therefore, the aging of plasma polymerized hexamethyldisiloxane (ppHMDSO) coatings that were subjected to helium or dry air plasma activation was investigated and compared to the aging of plasma activated silicone elastomer (S184) in this work. Water contact angle (WCA) measurements indicated that both materials reached a super-hydrophilic state after both plasma treatments. X-ray photoelectron spectroscopy (XPS) illustrated that this was the result of the introduction of a variety of oxygen-containing functionalities, while atomic force microscopy highlighted that the morphology was not significantly changed. The WCAs of the plasma activated ppHMDSO coating and S184 showed similar aging behavior, as the wettability of both materials significantly decreased. XPS measurements after 11 days of aging indicated that multiple aging processes were occurring in S184, while migration of oxidized short chain fragments was most important for the ppHMDSO coating. All these aged coatings could be silanized with 3-aminopropyltriethoxysilane, although differences in stability were observed. As such, this study provides additional insight in the chemical nature of activated plasma polymers and provides design principles for synthesizing plasma polymers with selective chemical functionalities.