Optical Emission Spectroscopy of Atmospheric-pressure Non-equilibrium DC Pulse Discharge Plasma Jets and PEN Film Surface Modification

To understand the mechanism of surface processing using atmospheric-pressure non-equilibrium plasma jets, we measured the vibrational and rotational temperatures in the plasmas by optical emission spectroscopy. Plasma was excited using a high-frequency pulsed power supply, using a gas mixture of Ar (20 L⁄min) and N2 (0.1 to 0.5 L⁄min) as the plasma gas, and changing the flow rate of N2 gas at an input power of 100 W and plasma frequencies of 5 and 10 kHz. The measured vibrational and rotational temperatures in plasma were approximately 0.18 to 0.26 eV and 0.21 to 0.28 eV, respectively. We also carried out a plasma surface processing of polyethylene naphthalate film to measure the changes in water contact angle before and after the processing. We found a monotonic decrease in the contact angle of the processed polyethylene naphthalate film as plasma rotational temperature increased. It is concluded that the hydrophilicity of the polyethylene naphthalate surface increases with plasma rotational temperature.