Effect of polycation structure on the fabrication of polyelectrolyte multilayer hollow fiber membranes for loose nanofiltration applications

Polyelectrolyte multilayer (PEM) membranes were fabricated by using a polycation with a long pendant group in order to prepare loose nanofiltration membranes. Poly(2-methacryloxyethyltrimethylammonium bromide)/poly (styrene sulfonate) multilayer membranes were prepared on the lumen side of polyethersulfone hollow fiber membranes with a dynamic coating method and compared to identically prepared poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) multilayer membranes to observe how the different polycation structures affect membrane properties. Both membranes were evaluated in terms of their water permeability, rejection of MgSO4, rejection of neutral polyethylene glycol model compounds, and stability against sodium hypochlorite at pH 8.0. Poly(2-methacryloxyethyltrimethylammonium bromide)-based membranes with loose nanofiltration properties and high water permeability were successfully fabricated. However, they degraded rapidly under sodium hypochlorite treatment, whereas the poly(diallyldimethylammonium chloride)-based membranes showed no significant degradation until after 50,000 ppm.h of sodium hypochlorite treatment. Despite the rapid degradation of poly(2-methacryloxyethyltrimethylammonium bromide)-based multilayers under the sodium hypochlorite treatment, the results show that choosing polyelectrolytes with appropriate side group structures can be attractive when designing PEM membranes with membrane properties in the loose nanofiltration range.