A Simple Approach to Surface Modification Using Polytetrafluoroethylene (PTFE) with Laminar and Turbulent Flows of Micro Plasma Jets at Atmospheric Pressure

Abstract

Unlike large area plasmas, small size plasma jets could be useful in treating localized regions. For this reason, we developed a micro plasma jet having a polytetrafluoroethylene (PTFE) part exposed to the discharge inside the plasma source. As the helium gas flow rate was raised from 0.1 to 6.0 slpm, the plasma exhibited a change in characteristic from laminar to turbulent and an abrupt change of appearance at a certain flow rate (2.0-3.0 slpm). The measured rotational temperature was above 500 K under laminar flow conditions, which was a sufficiently high temperature for the pyrolysis of PTFE, and the excitation temperature of the laminar flow was higher than that of the turbulent flow. The corresponding optical emission spectra were different (CN, C(2), FI, H(alpha) dominated for laminar conditions while N(2)(+), OH, OI dominated for turbulent flow conditions). These different plasma characteristics were obtained by simply controlling the gas flow rate. A feasibility study of surface modification demonstrated a change of the surface wettability from hydrophobic to hydrophilic (and vice versa) depending only on the gas flow rate.