Atmospheric-pressure plasma treatment on polystyrene for the photo-induced grafting polymerization of N-isopropylacrylamide

Atmospheric-pressure plasma (APP) treatment on polystyrene (PS) substrates by using N₂, He, and He/N₂ gases as working gas were investigated in this study, and photo-induced grafting polymerization of N-isopropylacrylamide (NIPAAm) on APP-treated PS substrates was subsequently applied. From the results of the wetting test, PS substrates treated by He-APP process represented a superior hydrophilicity with a contact angle of less than 10°. Surface analyses by X-ray photoelectron spectroscopy (XPS) indicated that functional groups of the carbonyl group (C = O) and carboxyl group (O-C-O) were generated on the surface of PS substrates after APP processes, which were most likely to enhance the surface hydrophilicity. Additionally, the thermosensitive poly-(NIPAAm) grafted on APP-treated PS substrates exhibited a hydrophilic surface (θ_H2O = 32°) below low critical soluble temperature (LCST), and converted into the hydrophobic surface (θ_H2O = 63°) as the ambient temperature exceeded LCST (> 33 °C). Our results suggest that the pre-treatment of PS substrates by APP process can increase the surface hydrophilicity and also be beneficial to the photo-induced grafting polymerization of NIPAAm on PS substrates.