Impact of cationic surfactants molecular structure on physicochemical structure and properties of polyamide reverse osmosis membrane via tailoring interfacial polymerization

Surfactants assisted interfacial polymerization (IP) has been demonstrated as an effective method to finely tailor the structure and performance of polyamide (PA) reverse osmosis (RO) membranes. However, little is done to illustrate how molecular structure of cationic surfactants affects IP and the amounts of surfactants incorporated into PA. In this study, three types of quaternary ammonium cationic surfactants were employed to assist the IP process and to fabricate RO membranes. Results show that these three cationic surfactants can not only significantly accelerate m-phenylenediamine (MPD) diffusion from aqueous phase into oil phase and promote the PA crosslinking, but also can be incorporated into PA to affect the surface properties (hydrophilicity, charge properties). Benzyl dimethyl phenyl ammonium chloride (BDMPAC) having two benzene rings had been found to be incorporated into PA with the highest amount because of its similar benzene structure as PA. Moreover, benzalkonium chloride (BAC) with the longest aliphatic tail induced a pronounced Marangoni convection during IP, resulting in an enlarged surface area of PA with large leaves and abundant internal/backside voids, and thus the highest water permeance. This study demonstrates a facile and simple way of using cationic surfactants to engineer the high-performance polyamide RO membrane.