Optimizing the surface modification of poly (tetrafluoroethylene) in a flowing afterglow Ar plasma

In the ideal tube-reactor, double Langmuir electron probe and electron spin resonance (ESR) were used to measure the distribution of electrons, ions and free radicals in Ar plasma. Surface modification of poly (tetrafluoroethylene) (PTFE) in Ar plasma active discharge zone and afterglow zone were studied respectively. The surface properties were characterized via the contact angle measurement, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the concentration of electrons and ions decreases rapidly with increasing the distance from the center of induction coil, which approximated to 0 at 30 cm, whereas the concentration of free radicals reduces slowly, which is 96% of initial one. The surface wettability of PTFE strongly depends on the plasma radio frequcency (RF) power, the treatment time and the argon flux. But regardless of conditions, Ar afterglow plasma is more effective than the conventional Ar plasma in PTFE surface modification because the enhanced reaction of radicals and the inhibited etching action of discharged particles. After a short treatment time (30 s) by Ar afterglow plasma, the surface composition of PTFE is modified and the F/C atomic ratio decreases from 3.27 to 2.30, O/C atomic ratio increases from 0.02 to 0.09. Both the defluorination from PTFE and introducing oxygen functionalities (e.g. CO) into PTFE surface are the primary reasons of surface wettability improvement.