Polyimide film surface modification by nanosecond high voltage pulse driven electrical discharges in water

Nanosecond high voltage pulses of 10 ns duration were used to generate pulsed discharges in distilled water for surface modifications of the aromatic and partially aromatic polyimides. Optical emission spectroscopy has shown the formation of excited speciesin plasma due to water dissociation and ionization. Molecular bands of hydrogen, oxygen, and nitrogen have dominated the emission spectra. The reactive species are likely to be responsible for the observed surface modifications of polymer films which were investigated by FTIR, AFM, XPS, and static contact angle measurements. The surface hydrophobicity of the polyimide films increased with treatment time. The mechanism of surface modification of polyimides treated by nanosecond pulsed discharges was different from previously described interactions with plasmas that were generated with microsecond voltage pulses. Nanosecond high voltage pulses have induced an increase of the unsaturated bondings on the polyimide surface, while the segregation of CF₃ groups at the film surface was responsible for the increased surface hydrophobicity when discharges were generated with microsecond high voltage pulses.