Ar plasma nanostructuring of PTFE for the wettability transition from hydrophobic to superhydrophobic and hydrophilic surfaces

Plasma processing of polymer surfaces like polytetrafluoroethylene (PTFE) has been extensively studied to achieve unique functional properties such as surface activation, desired wettability, surface adhesion, bonding, etc. Naturally, PTFE is hydrophobic with a water contact angle (WCA) of 105°. Hence, continuous efforts have been carried out to either increase or decrease the wettability of PTFE surfaces. However, as per the literature, the production of superhydrophobic PTFE by radiofrequency (RF) Ar plasma processing is challenging as it leads to defluorination and results in a hydrophilic surface. In the present study, the influence of RF power, plasma treatment time, impurities, and surface temperature on Ar plasma-treated PTFE was investigated. A single electrode-based arrangement with a sacrificial PTFE disc behind the sample was used for plasma discharge to avoid impurity and temperature effects. After 5 min treatment at 100 W, the surface became superhydrophobic (WCA=156°) due to the formation of nanostructures on the surface. However, 30 min of plasma treatment caused chemical changes and defluorination which resulted in a hydrophilic surface (WCA=14°). A yellowish layer was formed on the surface due to crosslinking, redeposition of fluorocarbon species, and iron impurities as confirmed by XPS analysis. Application of such surfaces for self-cleaning application will also be presented.