Abstract
One commonly used method to remove water from porous media is mechanical pressing. Applying stress to a material whose voids are filled with fluid causes the pores to collapse, driving out the liquid. When the porous medium is both elastic and hydrophilic, this dewatering process is reversible. After the applied stress is released, elastic recovery of the medium reopens pores, and capillary forces draw some of the expelled water back into the pore structure from whatever absorbent sink was adjacent to the material. Because the purpose of mechanical pressing is to remove liquid, preventing this reflux is key for optimizing dewatering efficiency. We investigated the impact of layering a stiff spacer at the interface of the material and sink such that dewatering occurs with minimal reflux. We hypothesize that this technique works by applying the Plateau-Rayleigh instability to achieve unidirectional transport. A spacer with the appropriate structure causes liquid channels to rupture as dewatering occurs. Although the driving force for reflux remains upon decompression, there is no path for flow. We find that this approach results in enhanced dewatering over a wide range of liquid properties. While other methods have previously been developed to promote unidirectional flow in porous media, our approach provides a solution where existing techniques fail to be practical. The main advantages of leveraging interfacial instability to prevent reflux include: a passive design with no moving parts, a structure with high permeability that does not restrict flow, and a rapid mechanism applicable to fast industrial processes.