Permeability and selectivity of 6FDA-6FpDA gas membranes prepared from different solvents

A set of different membranes from 6FDA6F, cast from different solvents, have been obtained and their gas permeability properties have been tested. Assuming that fractal dimension measures how the material fills a volume rather than a plane on the membrane surface, an increase in this parameter might be caused by a decrease in free volume of the material. This could explain the increase in selectivity and decrease in permeability observed in this work. 3. Results and discussion Roughness vs. scanned area pattern is characteristic of a given material and defines a fractal dimension that is evaluated as d = 3 – a where a is the so-called roughness exponent that can be calculated as the slope of roughness vs. scan size in a double log plot [3]. This fractal dimension represents well how roughness increases with scan size, with accurate fittings to experimental data. The resulting fractal dimensions for several membranes obtained from diverse solvents are shown in Table 1.