A comparative study of the effects of ammonia and hydrogen plasma downstream treatment on the surface modification of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was treated with hydrogen and ammonia microwave plasmas and the effects of treatment were evaluated by means of advancing and receding contact angle measurements, X-ray photoelectron spectroscopy, secondary-ion mass spectroscopy and atomic force microscopy analysis. Hydrogen plasma downstream treatment principally leads to defluorination and creation of C-C and C-H groups. This surface modification results in a slight decrease of the water contact angle and a large decrease of the methylene iodide contact angle. No evolution of the surface properties occurs over a period of at least two months following treatment. Ammonia plasma downstream treatment leads to defluorination and creation of C-C and C-H groups, as already observed with the H-2 plasma, but also to the introduction of nitrogen-containing groups. The modification produces a decrease of both water and methylene iodide contact angles. A large hysteresis is found with water contact angles due to the reorientation of the polar groups when the surface is in contact with a polar liquid. The surface modifications that result after a NH3 plasma treatment are less stable than after a HZ treatment. Nevertheless, after two days of ageing the water contact angle reaches a constant value, which is largely inferior to that of the untreated PTFE. Copyright (C) 1996 Elsevier Science Ltd.