Microstructure evolution of bonded water layer and morphology of grafting membrane with different polyethylene glycol length and their influence on permeability and anti-fouling capacity

In order to explore the distribution of hydrophilic moieties on the membrane surface and within the matrix, and to disclose the relationship among hydmphilicity, permeability and anti-fouling capacity, polyethylene glycol (PEG) with different molecular weight (M-w) was selected and the polyvinylidene fluoride (PVDF)/styrene-comaleic anhydride (SMA)-g-PEG flat membranes were prepared via esterification between SMA of the pristine membrane and PEG. The change of surface morphology of the grafting membrane was disclosed and the distribution of PEG on the surface and within the matrix was investigated. It was found that just as the changing trend of surface roughness, the skin-layer became thicker firstly and then thinner due to the surface degree of grafting (DG) and the bending of polymer chain. The microstructure of a bonded water layer (BWL), such as the thickness and tightness, was characterized via the force curve obtained by atomic force microscopy (AFM) and correlated with the DG and the length and conformation of the PEG chains. Finally, the influencing factors to flux, rejection and anti-fouling capacity were discussed from the points of the microstructure of BWL, wettability of the membrane and the resistance of the hydrophilic chain. The present work provides new information and a comprehensive understanding for the flux, rejection and anti-fouling capacity of membrane.