How Pore Hydrophilicity Influences Water Permeability?

Membrane separation is playing increasingly important role in providing clean water. Simulations predict that membrane pores with strong hydrophobicity produce ultrahigh water permeability as a result of low friction. However, experiments demonstrate that hydrophilic pores favor higher permeability. Herein we simulate water molecules transporting through interlayers of two-dimensional nanosheets with various hydrophilicities using nonequilibrium molecular dynamics. We reveal that there is a threshold pressure drop (Delta P-T), exceeding which stable water permeability appears. Strongly hydrophobic pores exhibit extremely high Delta P-T, prohibiting the achievement of ultrahigh water permeability under the experimentally accessible pressures. Under pressures < Delta P-T, water flows in hydrophobic pores in a running-stop mode because of alternative wetting and nonwetting, thus leading to significantly reduced permeability. We discover that hydrophilic modification to one surface of the nanosheet can remarkably reduce Delta P-T by > 99%, indicating a promising strategy to experimentally realize ultrafast membranes.