Plasma modification of PTFE surfaces Part II: Plasma-treated surfaces following storage in air or PBS

The mechanisms and kinetics of the ageing process of polytetrafluoroethylene (PTFE) samples stored in either phosphate-buffered saline (PBS) or air for periods of up to 1 month have been investigated. Changes of surface chemistry and wettability were studied as a function of ageing time using the complementary techniques of x-ray photoelectron spectroscopy, static secondary ion mass spectroscopy and dynamic contact angle measurements. Specimens were aged either in the as-received condition or after treatment by O-2, Ar, N-2 and NH3 plasma as described in Part I. Evidence was obtained for two ageing mechanisms, namely chemical reaction with the storage medium and relaxation in the surface region of the polymer. The extent of these mechanisms depended on the initial plasma treatment and the nature of the storage medium. These issues are discussed in a framework that correlates wettability with surface chemistry in a semiquantitative manner. This analysis facilitates comparison of the changes induced on virgin material by plasma treatment and ageing in storage environments relevant to the biomedical application of PTFE. Copyright (C) 2001 John Wiley & Sons, Ltd.