On the surface hydrophilization of a blended polysulfone membrane : Atomic force microscopy measurement and molecular dynamics simulation

This study elucidates a mechanism to improve fouling resistance for a polysulfone (PSf) membrane by blending polyvinylpyrrolidone (PVP). PSf is generally hydrophobic in nature and tends to be fouled by natural organic matter (NOM) due to a hydrophobic bonding during membrane filtration. Thus, to reduce hydrophobic bonding, a hydrophilic treatment is conducted using non-solvent induced phase separation, in which PVP is added to the PSf membrane. To investigate the chemical properties of the membrane surface, a surface elemental analysis using X-ray photoelectron spectroscopy and contact angle measurement of water droplets is conducted. It is found that, with an increase in PVP additive, macroscopic hydrophilicity increases. Next, to measure the surface adsorption of hydrophobic bonding, atomic force microscopy (AFM) is used. In this study, the AFM probe tip is chemically modified with hydrophobic matter that mimics hydrophobic NOM. With this AFM tip, contact force measurements are conducted in order to measure the absorption characteristics between the membrane surface and the NOM. Furthermore, a cross-flow filtration test is carried out to measure adsorption amounts of tannic acid (as a model hydrophobic substance) into the PSf membrane. Finally, these experimental results were phenomenologically investigated using a molecular dynamics simulation to clarify the hydrophilicity mechanism and improvement of anti-fouling performance of the membrane. © 2019 IOP Publishing Ltd.