The effect of membrane surface charges on demulsification and fouling resistance during emulsion separation

The effect of membrane surface charge on demulsification and fouling resistance during emulsion separation is investigated. By grafting poly(2-dimethylaminoethyl methacrylate) (pDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (pOEGMA) onto polypropylene (PP) membrane via ultraviolet (UV)-initiated polymerization, the obtained membranes PP- g -pDMAEMA and PP- g -pOEGMA present positive and negative surface charges in water, respectively. During the emulsion separation, PP- g -pOEGMA and PP- g -pDMAEMA membranes exhibit different separation efficiencies and pollutant resistant behaviors to the emulsions prepared from anionic surfactant (sodium dodecyl sulfate, SDS) and cationic surfactant (cetyltrimethylammonium bromide, CTAB). Comparing to PP- g -pOEGMA, the separation efficiency of PP- g -pDMAEMA was 15% (SDS emulsion) and 300% (CTAB emulsion) higher. But the flux recovery ratio of PP- g -pOEGMA was raised 30% (SDS emulsion) and 16% (CTAB emulsion). Hence, the membrane surface positive charges assist demulsification, but aggravate the membrane fouling . The mechanism obtained is beneficial to construct membranes with high separation efficiency and long-term durability.