Preparation and performance of dynamic layer-by-layer PDADMAC/PSS nanofiltration membrane

Dynamic layer-by-layer (LBL) self-assembly technology was used to prepare as few as three to five bilayers of poly(diallyl-dimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) on negatively charged polysulfone (PS) ultrafiltration (UF) membranes of 50 kDa MWCO and compared with those of the static assembly membranes. The prepared dynamic assembly (PDADMAC/PSS)4 nanofiltration (NF) membrane showed a permeation flux of 60 L m−2 h−1 at 1.0 MPa, much higher than that of the commercial DL membrane (GE Osmonics, USA), but with a rejection of about 90% of SO42− which is relatively less than that of the DL membrane. The rejection performance showed that the dynamic–static assembly was more effective than others. Using dynamic–static assembly preparation, the rejection of (PDADMAC/PSS)3 membrane was about 90%, while the flux was about 55 L m−2 h−1 at 1.0 MPa. The surface morphology of the prepared LBL membranes were characterized by SEM and AFM, and no defect was found. The surface morphology of the membrane prepared by dynamic–static assembly was almost the same as the commercial membranes. The analysis of filtration resistance indicated that the deposition of the first and second bilayer was crucial during the whole preparation process.

► A novel cross-flow dynamic–static self-assembly preparation method has been proposed.
► Different swelling polyelectrolyte should be assembled by different method.
► The novel preparation method can decrease the LBL bilayers considerably.
► The prepared (PDADMAC/PSS)3 NF membrane has relatively smaller surface roughness.
► The prepared (PDADMAC/PSS)3 NF membrane has excellent separation performance.