Giant Effect of Negative Compressibility in a Water-Porous Metal-CO₂ System for Sensing Applications

When compressed, the size of ordinary materials reduces. The opposite effect, when a material or system increases (decreases) its volume upon compression (decompression), is called Negative Compressibility (NC). NC is extremely rare, while being attractive for a wide range of applications. Here we demonstrate, by both experiments and MD simulations, a pronounced effect of volumetric NC in a system consisting of water, porous metal and CO₂. This effect is achieved due to a new extrusion-adsorption cycle of water from-into a porous metal driven by a wetting-nonwetting transition due to the increase-decrease of CO₂ pressure. The heterogeneous nature of such a system leads to unprecedented NC of up to ∼ 90% in a narrow pressure range, meaning that almost a double volume increase (decrease) upon compression (decompression) is achieved. As long as the wetting-nonwetting transition is achieved, the proposed approach is not limited to water and a specific porous metal. An example of the application of this phenomenon is miniature sensors, particularly for threshold CO₂ pressure detection.