Surface Modification of Polytetrafluoroethylene by Atmospheric-Pressure Plasma Jets

Abstract

The change of polytetrafluoroethylene surface properties under the influence of nonthermal nonequilibrium plasma generated by plasma jets at atmospheric pressure is shown. The unsteady form of diffuse discharge, a glow discharge, which is superimposed on weak-current spark discharges, is experimentally realized and formed in the gas flow in the form of atmospheric pressure plasma jets. The plasma jet (diameter of the plasma jet is 2.5 cm, length of the jet is 1–2 cm) is oriented perpendicularly to the surface of polytetrafluoroethylene. Water contact angle measurements and electron microscopy are used to determine the surface characteristics of the material. An intensive and homogeneous improvement of the polymer surface wettability is observed on a large area (contact area S ≈ 7 cm²) subjected to plasma treatment during the first seconds of exposure to the plasma jet. The contact angle of the original polytetrafluoroethylene with a drop of water is 102°, while the contact angle θ decreases to 65° when exposed to plasma jets. In the area of plasma jets impact at atmospheric pressure, in contrast to the original surface, there are pronounced inhomogeneous surface formations, and at the interface a sharp change in the wettability of the surface is observed. On the surface of polytetrafluoroethylene sample in the area of plasma jets impact, the percentage of carbon increases, while the percentage of fluorine decreases.