Surface morphology of homogeneous and asymmetric membranes made from poly(phenylene oxide) by tapping mode atomic force microscope

Abstract

Surface morphology of asymmetric and homogeneous membranes prepared from poly(phenylene oxide) (PPO) was studied by tapping mode atomic force microscopy (TM AFM). As expected, a significant difference in the morphology between the top and the bottom surfaces of the asymmetric membrane was observed. The images of the top surface revealed a small variation in the vertical direction (6.7 nm), compared to the mean diameter of nodules (62 nm), while the images of the bottom surface were very porous (microfiltration structure). On the other hand, the observed difference in morphology between the top and the bottom surfaces of the membrane prepared by the complete evaporation of the solvent (homogeneous membrane) was rather unexpected. The nodules on the bottom surface were twice as large as those on the top surface. These studies also revealed some differences in the morphology of the top surface of asymmetric and homogeneous membranes. Both surfaces were made up of nodules having a similar size (62-64 nm) ; however, roughness parameters calculated for the top surface of the asymmetric membrane were approximately two times greater than those for the top surface of the homogeneous membrane.