Rates of air flow in and out of closed atmospheric-pressure plasma jet system affected surface properties of treated polysulfone membrane

The cold plasma jet works in an atmospheric-pressure condition, and is used to modify polymer membranes by creating hydrophilic functional groups on the membrane surface. Since it can be used without a pressurereducing system, treatment time and cost are reduced. However, the plasma jet has a narrow beam which limits the area of the membrane surface that can be activated. In this study, a plasma jet was generated in a closed system with controllable rates of air flow in and out of the system. The plasma discharge was recorded with a camera and analyzed by optical emission spectroscopy (OES). Polysulfone membrane surfaces were treated with various conditions of plasma discharge, and the induced membrane hydrophilicity was assessed from water contact angle (WCA) and surface energy (SE) measurements. Atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and WCA contour mapping were respectively employed to study surface roughness, functional groups, and WCA distribution on the treated membrane surfaces. The airflow had distinctly different effects on the plasma characteristics. The inflow rate condition affected the width of the plasma beam, and the outflow rate condition affected the diffusion of the plasma beam. Water flux was changed according to the plasma characteristic, and an air outflow rate of 6 L/min was the optimum condition for this experiment.