SURFACE FLUORINATION OF COMPOSITE MEMBRANES .2. CHARACTERIZATION OF THE FLUORINATED LAYER

The fluorinated surface layer of membranes exposed to a dilute stream of fluorine gas has been characterized. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy attenuated total reflection (FTIR-ATR) were used to determine the concentration and profile of reacted fluorine in poly (4-methyl-1-pentene) membranes after exposure to fluorine. The thickness of the fluorinated layer as a function of reaction time was calculated using the results of bulk elemental analysis and of XPS. The permeability of this layer was determined using the calculated thickness and the (P(f)/l(f)) values reported previously. It is shown that the permeability of the fluorinated material is two orders of magnitude lower than that of the original poly(4-methyl-1-pentene). A simple diffusion limited reaction model is able to give a good estimate of the thickness of the fluorinated layer as a function of fluorine reaction time.