An All Hydrophilic Fluid Diode for Unidirectional Flow in Porous Systems

A fluid diode that allows fluid flow in one direction but blocks fluid flow in the opposite direction has wide applications including oil recovery, drug delivery, and lab-on-a-chip microfluidics. Many studies are conducted to facilitate directional liquid motion on the solid surface or across thin porous layers. However, the self-driven one-way flow inside porous systems still remains a significant challenge. Here, a novel all-hydrophilic fluid diode (AHFD) made of porous materials with asymmetric pores is reported, which allows capillary flow in a chosen direction. The direction-dependent flow process and the breakthrough pressure are experimentally and theoretically examined. The proposed AHFD can have many potential applications such as functional protective clothing, microfluidic valve, and oil-water separator, and the idea can be extended to develop other all lyophilic fluid diodes such as oleophilic diode.