The investigation of adhesion force of support membrane on the structure and performance of nanofiltration membrane

The surface properties of non-porous areas (>90 %) of support membranes were often overlooked to influence the performance of nanofiltration (NF) membranes. In this work, the role of the support membrane in interfacial polymerization (IP) during synthesis of NF membrane and consequently on its performance were quantitatively investigated from the perspective of adhesion force for the first time. The support membranes with considerable pore structures and different surface sulfonate (-SO 3 - ) contents were prepared from different concentrations of polyethersulfone/sulfonated polysulfone (PES/SPSf) solutions. The adhesion forces of different support membranes were measured by atomic force microscope (AFM). The IP process between piperazine (PIP) and trimethylbenzoyl chloride (TMC) and the obtained polyamide (PA) layer on the support membranes were monitored by Quartz crystal microbalance with dissipation (QCM-D). The results indicated that the contents of sulfonic groups on the surface of the support membranes decreased as the casting-solution concentration increased (from 16 % to 28 %) due to a negative segregation phenomenon, which resulted in a decrease in the adhesion force (from 17.9 to 2.6 nN) between the support membranes and PIP monomers. The reduced adhesion force between the support membrane and PIP monomers led to an increase in the PA layer thickness (from 0.8 to 18 nm). Interestingly, the time to reach PA layer thickness equilibrium decreased (from 91 to 23 s). The obtained NF membranes (from PA@PES/SPSf 16 to PA@PES/SPSf 28 ) achieved the pure water permeance from 51.2 to 26.2 L m −2  h −1 ·bar −1 while the salt (Na 2 SO 4 ) rejection from 97.5 to 99.5 %, respectively, was noted. It was demonstrated that controlling the adhesion force between the support membranes and PIP monomers could effectively regulate the structure and the performance of NF membranes. This work would provide valuable insights for designing high-performance NF membranes in practical applications.