Surface fluorination of poly (phenylene oxide) composite membranes: Part II. Characterization of the fluorinated layer

Abstract

Composite membranes, comprising a selective layer of poly (2,6-dimethyl-1,4-phenylene oxide) on a microporous ceramic support, were surface fluorinated under mild conditions. The treatment parameters, fluorine feed concentration and treatment time, were each varied independently while the other parameter was kept constant. The fluorinated region was characterized using dynamic contact angle analysis and X-ray photoelectron spectroscopy (XPS). The fluorine to carbon ratio increased as a function of treatment time, but showed little variation when the feed concentration was varied. A relatively high oxygen to carbon ratio was observed which showed little change over the range of fluorination conditions. Angle-dependent XPS showed the concentration of fluorine species to be higher at greater depths below the surface. Fluorination times of 5 to 7 min minimized the water contact angle and maximized the total and polar surface free energies. Water contact angles decreased after fluorination but showed no definite trend as a function of feed concentration. The composition of the fluorinated region is discussed in relation to the gas transport properties of membranes fluorinated under similar conditions (Part I of this study).