Transition between stable hydrophilization and fast etching/hydrophilization of poly(methyl)methacrylate polymer using a novel atmospheric pressure dielectric barrier discharge source

Abstract

Tuning the transition between stable hydrophilicity and high etching-rate and simultaneous hydrophilization of polymethylmethacrylate (PMMA) films was achieved in an open-air environment simply by adjusting the O2 content in He gas injection through the showerhead-type electrode of a novel atmospheric pressure dielectric barrier discharge source. A comparative study was performed for He and He-O2 plasma treatment of PMMA. Electrical and optical measurements indicated severe alteration of plasma characteristics when O2 is added in gas feed. The enhancement of oxygen emission band intensities indicates an enhanced concentration of atomic oxygen, resulting in very high PMMA etching rates of ∼320 nm/min, ∼four times higher compared to pure He. In contrast, the He plasma showed higher nitrogen emission band intensities, translated into a higher nitrogen content on the PMMA surface according to x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. This enhanced nitrogen content due to the partial substitution of ester groups of the PMMA side chain with amide groups was responsible for the more efficient hydrophilization of the PMMA surface. A water contact angle as low as ∼28° was achieved, stabilizing at ∼40° after 10 days and remained constant at least for 45 days, significantly lower than that for the untreated PMMA (∼69°).