Tunable hydrophilic modification of polyethylene terephthalate membrane via layer-by-layer polyethylenimine grafting

Hydrophilicity is an important property for membranes as it influences the application scope and effectiveness of separation process, and various surface modification methods have been developed targeting to an enhanced hydrophilicity. However, few work focuses on hydrophilicity tunability, and many researches can only obtain limited wettability improvement. Here, a novel surface modification method is reported. In this method, surface functional groups on polyethylene terephthalate membrane are activated and hydrophilic polyethylenimine chains can be grafted to the membrane in a layer-by-layer manner. The membrane hydrophilicity is thus tunable in a wide range through adjusting the number of grafting steps, and a water contact angle decrease of 54^o that exceeds most of other grafting modification methods is achieved. Optimal membrane hydrophilicity corresponding to a contact angle of 60^o is found through the screening for the highest water permeability, and a water permeability improvement of ∼29 % is observed for modified PET track-etched membranes with different parameters.