Investigation on the stability and antifouling properties of polyvinylidene fluoride (PVDF)-zwitterion mixed matrix membranes (MMMs) using molecular dynamics simulation (MDS)

In this study, molecular dynamics simulation (MDS) was employed to investigate the stability, hydrophilicity and oil-antifouling capacity of Mixed Matrix Membrane (MMM) prepared from polyvinylidene fluoride (PVDF) membrane matrix, zwitterion (ZW) and titanium dioxide nanoparticles (TiO2 NPs) as nanofillers. Large-scale Atomic/Molecular Massively Parallel Software (LAMMPS) with Dreiding force field was used to compute atomic and molecular interactions of MMM, water-MMM and oil-MMM models. Computed potential energy and binding energy were analysed to assess the stability of MMM and the retention of nanofillers, while hydrogen bonding energy and number of hydrogen bonds induced was used to evaluate the membrane hydrophilicity. In addition, oil-antifouling property was assessed according to oil-MMM binding energy, Mean-Squared Displacement (MSD) and Radial Distribution Function (RDF). Two different membrane preparation approaches were studied and compared: 1) zwitterions are initially grafted on TiO2 nanoparticles, then immobilized into PVDF membrane matrix, 2) zwitterion and bare TiO2 nanoparticles are blended into PVDF membrane matrix. The objectives were to assess the impacts of ZW types and membrane synthesis approach on MMM's stability and performance using different ZWs (carboxybetaine (CB) phosphorylcholine (PC) and sulfobetaine (SB)). The MDS results showed that both zwitterionic type and membrane preparation method had influences on MMM's stability, hydrophilicity and oil-antifouling capacity. Positive computed potential energy and binding energy suggested that nanofillers-PVDF interactions were thermodynamically unstable so that nanofillers would aggregate during membrane preparation process. Overall, ZW-uncoated-NP MMMs were more stable and exposed lower degree of nanofillers aggregation, thereby anticipated higher nanofillers retention. In addition, ZW-uncoated-NP MMMs displayed higher hydrophilicity caused by high number of hydrogen bonds and hydrogen bonding energy with water. ZW-uncoated-NP MMMs also exhibited higher oil-antifouling capacity as compared to ZW-coated-NP MMMs. Comparison of the performance of different zwitterions suggested that PC was the most preferable candidate which could induce stable harmonized MMMs, high nanofillers retention, strong hydrophilicity and oil-antifouling capacity.

Automated summary

This study employed molecular dynamics simulation to investigate the stability, hydrophilicity, and oil-antifouling capacity of Mixed Matrix Membranes prepared from polyvinylidene fluoride membrane matrix, zwitterion, and titanium dioxide nanoparticles. The results showed that both zwitterionic type and membrane preparation method influenced the membrane's stability, hydrophilicity, and oil-antifouling capacity. ZW-uncoated-NP MMMs exhibited higher stability, hydrophilicity, and oil-antifouling capacity compared to ZW-coated-NP MMMs, with phosphorylcholine appearing as the most preferable zwitterion for stable and effective MMMs.