pH-Responsive Janus membrane with liquid gating property for crop protection and demulsification

Liquid directional transport plays a major role in microfluidic systems and liquids separation. Although Janus membrane (JM) with asymmetric wettability exhibits significant advantages in liquid directional transport, selective passage relying on the recognition of liquid pH is seldom reported. Furthermore, exploring novel and potential functions for JM remains highly significant. Here, a flexible and robust JM with pH response (JM-pH) acting as the liquid gate to distinguish liquids with different pH has been developed. Among them, one side with super-hydrophobicity was fabricated by electrospinning, and the other side with acid-repellence and alkali-affinity was formed via a graft polymerization. Then, the unidirectional transport mechanism of liquids was elucidated by analyzing the Laplace pressure, hydrophobic force, capillary force, and the reaction of protonation and deprotonation at the solid–liquid interface of the JM-pH. Surprisingly, the JM-pH showed an innovative performance that can protect crops from being corroded by acid rain and enhance the insecticide utilization. Furthermore, an alkali pre-wetted strategy was proposed to allow either water or oil to pass through the JM-pH, which achieved the demulsification of oil water mixtures. Consequently, the unique advantages of the JM-pH provide feasibilities for protective surfaces with liquid directional transport and on-demand demulsification.