Polyelectrolyte membranes prepared by dynamic self-assembly of poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) for nanofiltration (I)

In recent years, the layer-by-layer (LBL) self-assembly of polyelectrolyte has attracted much attention for the preparation of nanofiltration (NF) membranes. However, most researchers focused on the homopolymers, few studied on the copolymers for the preparation of NF membranes. In the present work, a series of nanofiltration membranes were prepared by dynamic self-assembly of a copolymer polyelectrolyte containing both weakly and strongly ionized groups, poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA), with poly (allylamine hydrochloride) (PAH) and poly (styrenesulfonic acid sodium salt) (PSS) on the modified polyacrylonitrile (PAN) ultra-filtration membranes. The effects of substrate, deposition pH, SS/MA ratio in PSSMA, concentration of the PSSMA and bilayer number on the properties of the NF membranes were investigated. The results indicated that the performances of the NF membranes prepared by dynamic self-assembly process were superior to those prepared by the static self-assembly process. The membranes terminated with PSSMA were negatively charged. Due to the changes of charge density and conformation of PSSMA in different pH conditions, the PAH/PSS]₁PAH/PSSMA membrane prepared at pH 2.5 showed higher Na₂SO₄ rejection and larger flux than those of the membrane prepared at pH 5.7. The NF membrane PAH/PSS]₁PAH/PSSMA composed of only two bilayers exhibited 91.4% Na₂SO₄ rejection and allowed solution flux of 28.6 L/m² h at 0.2 MPa. The solution flux increased to 106.6 L/m² h at 0.8 MPa, meanwhile, no obvious decrease in Na₂SO₄ rejection was observed.