Surface chemistry and wettability of plasma-treated PTFE

Polytetrafluoroethylene sheet samples have been treated in a low-power plasma cell using O2, Ar, N2 and NH3 feed gases. The surfaces became significantly more wettable in simulated body fluid and bromonaphthalene. By using a range of techniques, this was found to be principally due to chemical changes at the surface induced by the plasma treatments. Static SIMS and XPS showed that these changes were defluorination and incorporation of unsaturated hydrocarbons and oxygen-containing moieties. The extent of these changes depended on the feed gas used, being least for O2 and greatest for Ar. In addition, it was found that surfaces became activated by the plasma treatments and continued to change chemically during subsequent storage in simulated body fluid. By contrast, storage in air resulted in partial recovery towards the untreated surface state, which was attributed to relaxation processes in the modified layer.