Comparison of gas separation performance and morphology of homogeneous and composite PPO membranes

Based on AFM observations and solvent evaporation kinetics, it is postulated that the enhancement in the selectivity and the drop in the gas permeability of the coated layer, in comparison to that of the dense homogeneous membrane, is due to the densification and compaction of the polymer adjacent to the support membrane interface. This is the direct result of the migration of solvent toward the support membrane and the partial draw of the solvent into the support membrane pores. This has produced a smoother bottom surface as a result of (i) the formation of small nodules, and (ii) the fusion of these small nodules by the compressive forces that have developed due to the shrinkage of the swollen support substrate. These compressive forces have caused the bottom surface to wrinkle.