Wettability Switchable Membranes for Separating Both Oil-in-water and water-in-oil emulsions

Separation membranes with switchable wettability show great potential in the efficient treatment of both oil-in water and water-in-oil emulsions. There still remain some critical challenges to prepare these membranes by a facile procedure and to elucidate the wettability response mechanism reasonably. Herein, commercial polypropylene membranes are endowed with switchable surface wettability by a simple co-deposition method of tannic acid and diethylenetriamine. The as-fabricated membrane surfaces are hydrophilic due to water immersion but hydrophobic after ethanol treatment. This hydrophilicity-hydrophobicity translation can repeat cyclically by water/ethanol treatments without losing the surface wettability. DFT simulations are used to calculate the solvation free energies of tannic acid in water and ethanol, respectively, to illustrate the chemical mechanism of the hydrophilicity-hydrophobicity translation. The results are in accordance with UV?vis spectra of the polyphenol in both solvents. The wettability switchable membranes show great potential in separating both oil in-water and water-in-oil emulsions with excellent efficiency (98%). Moreover, the driving force for the separation processes can be an applied pressure of 0.1 MPa or merely the gravity of emulsions.