Nanoscale Heterogeneity of Polyamide Membranes Formed by Interfacial Polymerization

The nanoscale structure of composite polyamide reverse osmosis (RO) and nanofiltration (NF) membranes was investigated by transmission electron microscopy and atomic force microscopy. The study demonstrated that the polymer density and charge are distributed across the active polyamide layer in a highly nonuniform fashion. The polyamide films appear to be built of a negatively charged outer layer sitting on top of an inner layer possessing a small positive charge. This picture appears to be fairly general for all types of composite membranes and seems to reconcile previously reported contradictory experimental facts concerning measurements of charge for this type of membrane. The sharp boundary between the…