Environ. Sci. Technol. 2004, 38, 3168-3175
Swelling and Morphology of the Skin Layer of Polyamide Composite Membranes: An Atomic Force Microscopy Study VIATCHESLAV FREGER* Laboratory for Desalination and Water Technology Research, Institutes for Applied Research, Ben-Gurion University of the Negev, P.O. Box 635, Beer-Sheva 84105, Israel
The paper introduces a new methodology for studying polyamide composite membranes for reverse osmosis (RO) and nanofiltration (NF) in liquid environments. The methodology is based on atomic force microscopy of the active layer, which had been separated from the support and placed on a solid substrate. The approach was employed to determine the thickness, interfacial morphology, and dimensional changes in solution (swelling) of polyamide films. The face (active) and back (facing the support) surfaces of the RO films appeared morphologically similar, in agreement with the recently proposed model of skin formation. Measured thickness and swelling data in conjunction with the intrinsic permeability of the membranes suggest that the selective barrier in RO membrane constitutes only a fraction of the polyamide skin, whereas NF membranes behave as nearly uniform films. For NF membranes, there was reasonable correlation between the changes in the swelling and in the permeability of the membrane and the salinity and pH of the feed.
Introduction Polyamide composite membranes currently dominate the field of reverse osmosis (RO) and nanofiltration (NF) (1, 2). Membrane desalination based on RO has today become the key technology for the production of freshwater from saline sources. As opposed to RO membranes, which effectively reject all inorganic solutes, polyamide membranes for NF are capable of selective removal of certain solutes, while allowing the passage of others (2, 3). RO and NF polyamide membranes are made up of an ultrathin (
