Effect of the physicochemical properties on the permeation performance in fully aromatic crosslinked polyamide thin films

Abstract Thin‐film‐composite reverse‐osmosis (RO) membranes were prepared by the interfacial polymerization of trifunctional 1,3,5‐benzentricarbonyl chloride (TMC) with difunctional 1,3‐benzendiamine (MPDA) or 1,4‐benzendiamine (PPDA). The meta‐positioned polyamide (MPDA/TMC) resulted in higher water flux but lower salt rejection than the para‐positioned polyamide (PPDA/TMC). To understand this behavior, we studied various factors including the thickness, rupture strength, chemical properties, and solubilities of the water and salt in the thin‐film polyamide. The thin films made from MPDA and PPDA possessed similar thicknesses and rupture strengths adequate for withstanding the RO operation pressure. However, the meta‐positioned polyamide had higher hydrophilicity and greater molecular chain mobility than the para‐positioned polyamide, resulting in higher water flux. In contrast, the para‐positioned polyamide had lower salt solubility and lower molecular chain mobility than the meta‐positioned polyamide, thereby possessing higher salt rejection. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 569–576, 2003