Effects of Oxygen Plasma and Dopamine Coating on Poly(Vinylidene Fluoride) Microfiltration Membrane for the Resistance to Protein Fouling
Poly(vinylidene fluoride) (PVDF) membrane was widely employed for filtration owing to its good mechanical property, thermal stability, and solvent resistance. However, the hydrophobic surface of PVDF might result in protein adsorption and the reduction of permeate flux. This paper proposed two approaches, O2 plasma treatment and dopamine coating, to study the protein fouling behavior on PVDF membranes. Both O2 plasma modified and dopamine coated PVDF membranes showed reduced water contact angles. Moreover, O2 plasma resulted in higher surface area and higher surface electronegativity, while dopamine coating caused the reduction of total surface area of membrane and imparted positive charges. electron spectroscopy for chemical analysis characterizations confirmed the presence of oxygen functionalities that validated the functionalities accounted for the negative charges. The fouling resistance to bovine serum albumin (BSA) was promoted by O2 plasma treatment, where the time to reach fouling was delayed by more than 10 min and the flux was higher on the modified PVDF than that on the pristine membrane. Further reduction of membrane fouling was achieved by prolonging the plasma treatment time, which resulted in more negatively charged PVDF surface. On the other hand, rapid flux reduction was observed on the dopamine coated PVDF membrane, whereas the resistance to protein was limited. The results of dynamic BSA adsorption indicated that the membrane fouling was affected by the overall resulted surface properties including surface electrical charge, surface wettability, and surface area. Moreover, oxygen plasma treatment proved to promote the filtration performance effectively, which is presumably due to the surface charge effects. On the other hand, the adhesive dopamine coating resulted in stronger protein adhesion and therefore fast flux loss. The obtained results provide alternative surface modification methods for microfiltration membranes with higher efficiency and better fouling resistance.