Effect of discharge gases on microwave plasma reactions of imidazole on poly(dimethylsiloxane) surfaces: Quantitative ATR FT-IR spectroscopic analysis

Although our recent studies revealed that under Ar microwave plasma conditi ons reactions of imidazole with poly(dimethylsiloxane) (PDMS) result in the formation of Si-CH2-imidazole species, the issue of the discharge gas effe ct on microwave plasma reactions remain unanswered. This study examines how these reactions in the presence of Ar, O-2, and CO2 gases under microwave plasma conditions will affect surface reactions on PDMS in the presence of imidazole vapors. When Ar microwave plasma reaction conditions are employed , imidazole molecules react to the PDMS surface through hydrogen abstractio n of the N-H bonds to form Si-CH2-imidazole and Si-CH2-CH3 linkages. When O -2 microwave plasma reactions are conducted for 20 s or less discharge time s, Si-O-imidazole and Si-O-CH3 species on the PDMS surface are formed. On t he other hand, for discharge times above 20 s, the Si-O-CH3 linkages are co nverted to Si-O-CH2-imidazole entities as a result of hydrogen abstraction. The CO2 microwave plasma reactions in the presence of imidazole vapors res ult in the formation of Si-O-imidazole-CH3 species on the PDMS surface, fol lowed by hydrogen abstraction, resulting in the formation of Si-O-imidazole -CH2. radicals, which react with subsequent imidazole molecules through the formation of CH2-N linkages. Similarly to the previous studies, quantitati ve ATR FT-IR surface analysis showed that the highest yields of imidazole r eactions occur under O-2 microwave plasma conditions. All experiments utili zed in this study allowed surface analysis at 1.3 mu m from the surface.