SURFACE FLUORINATION OF COMPOSITE MEMBRANES .1. TRANSPORT-PROPERTIES

The potential utility of surface fluorination for improving the gas separation properties of a polymer membrane was investigated using poly(4-methyl-1-pentene). It was found that fluorination leads to a reduction in flux accompanied by a very significant increase in selectivity and that after this initial change these trends continue to a lesser degree for up to one year after fluorination. An idealized composite structure consisting of a fluorinated layer with unfluorinated material comprising the rest of the thickness is used to visualize the structure of these membranes. The series resistance model is used to illustrate the relationship between the total membrane thickness and the fraction that the fluorinated polymer layer contributes to the total. This relationship was demonstrated experimentally by fluorinating composite membranes with a permselective poly(4-methyl-1-pentene) layer ranging in thickness from 0.2 to 20-mu-m. The transport of six gases was measured. The series resistance model was used to estimate the transport properties of the fluorinated polymer layer.