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A comparative study of polytetrafluoroethylene (PTFE) surfaces treated by thepost-discharge of He and He-O2 plasmas at atmospheric pressure is presented.The characterization of treated PTFE surfaces and the species involved in thesurface modification are related. In pure He plasmas, no significant change ofthe surface has been observed by X-ray photoelectron spectroscopy (XPS),dynamic water contact angles (dWCA) and atomic force microscopy (AFM), in spiteof important mass losses recorded. According to these observations, alayer-by-layer physical etching without any preferential orientation isproposed, where the highly energetic helium metastables are the main speciesresponsible for the scission of --(CF2)n-- chains. In He--O 2 plasmas, as thedensity of helium metastables decreases as a function of the oxygen flow rate,the treatment leads to fewer species ejected from the PTFE surfaces (inagreement with mass loss measurements and the detection of fluorinated speciesonto aluminum foil). However, the dWCA and AFM measurements show an increase inthe hydrophobicity and the roughness of the surface. The observed alveolarstructures are assumed to be caused by an anisotropic etching where the oxygenatoms etch mainly the amorphous phase.

Etching Processes of Polytetrafluoroethylene Surfaces Exposed to He and He-O2 Atmospheric Post-discharges