Unveiling Unidirectional Transport within Janus Membranes

Janus membranes with unidirectional transport capacity have shown broad potential across various fields of mass–energy transmission and conversion. However, the underlying mechanisms driving this transport remain unclear. In this study, a three-stage model—encompassing liquid intrusion, capillary wetting, and liquid transport—is proposed to elucidate the unidirectional liquid transport within Janus membranes. Finite element analysis reveals two key mechanisms: direct contact-driven liquid intrusion in bilayer structures and surface-energy-driven intrusion in gradient structures. It is also demonstrated that capillary forces within the hydrophilic pores predominantly control the second stage, while droplet Laplace pressure dictates continuous liquid transport at the last stage. Furthermore, critical structural parameters that influence the transport process are identified, aligning with experimental observations. These findings lay a theoretical foundation for optimizing the Janus membrane structures and expanding their applications.