Hydrophobic to superhydrophobic and hydrophilic transitions of Ar plasma-nanostructured PTFE surfaces

Production of superhydrophobic polytetrafluoroethylene (PTFE) by Ar plasma etching is challenging as it leads to defluorination, resulting in a hydrophilic surface. The effect of radiofrequency power, treatment time, impurity, and surface temperature on Ar plasma-treated PTFE was investigated for producing a large-area superhydrophobic PTFE surface. To avoid impurity and substrate temperature effects, a single electrode-based arrangement with a sacrificial PTFE disc behind the specimen was used for plasma discharge. After 5 min treatment at 100 W, the surface became superhydrophobic (water contact angle = 156 degrees) due to the formation of isotropic nanostructures. However, 30 min of plasma treatment caused severe chemical changes resulting in a hydrophilic surface (water contact angle = 14 degrees). A yellowish layer was formed on the surface due to crosslinking, redeposition of fluorocarbon species, and iron impurities from the plasma system confirmed by X-ray photoelectron spectroscopy analysis.