Electric Field-Induced Underwater–Oil Diode on a Janus-Porous Ion-Doped Polypyrrole Membrane

Directional liquid transport on the surface is of great significance in liquid collection, transfer, and separation. Despite extensive research on surface wetting control, achieving unidirectional liquid permeation on material surfaces under water remains a challenge. Here, we demonstrate that electric field-induced unidirectional oil permeation can be achieved on a Janus-porous ion-doped polypyrrole membrane (Janus-PIPM). The results indicate that the competition between the liquid spread and permeation is crucial for achieving unidirectional liquid permeation. By designing and adjusting the dimensions of the pore structure and integrated mode, Janus-PIPM can be used to regulate the liquid transport behavior, i.e., spread or permeation. Furthermore, with the cooperation of an electric field, the Janus-PIPM with a specific pore size can realize the unidirectional oil permeation, which can be used as an electric field-responsive underwater-oil diode. Therefore, Janus-PIPM can serve as a valve for smart unidirectional liquid transportation and has broad prospects for applications in areas such as gate control switches, microreactors, microfluidic transport, and so on.