Characterization of membranes prepared from PPO by Raman scattering and atomic force microscopy

The surface structures of dense (homogeneous) and asymmetric (integrally skinned) membranes made from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) in chloroform and in 1,1,2-trichloroethylene were investigated by Raman spectroscopy and by tapping mode atomic force microscopy (TM AFM). Results revealed by Raman spectroscopy indicated that the ''state of the polymer'' in the polymer powder and in the membranes prepared from PPO by using different solvents was not identical. A significant perturbation in the Raman scattering was observed in the asymmetric membrane prepared from PPO by using CHCl3 (PPO-CHCl3). A difference in the morphology of the surfaces (top and bottom) was also observed by TM AFM. It is believed that faster evaporation rates resulting from the use of a more volatile solvent, results in preserving more of the polymer structure present in the solution. Therefore, nodules produced from polymer dissolved in more volatile solvents might contain more free volume entrapped inside nodules, which results in larger dimensions of nodules compared to those produced from polymer dissolved in a less volatile solvent. This was confirmed by the larger dimensions of nodules and the higher permeation rate of CO2 in the membranes prepared from PPO-CHCl3 solution compared to those prepared from PPO-TCE solution.