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Experimental data on the interfacial tension of ionic liquids in CO 2 and CH 4 atmospheres at elevated pressures (up to 20 MPa and 353 K) are presented and discussed. In addition, molecular modeling is utilized to describe the thermophysical properties under process-relevant conditions. Molecular modeling has the potential to predict findings in order to avoid costly experiments in the future and to explain the principal behavior of the whole system in terms of simulated concentration profiles. The interfacial tension is recognized to be an important quantity in a number of processes, e.g., for describing multiphase flow. By dissolving within the liquid phase, gases reduce the interfacial tension, which in turn is closely related to the phase behavior. It is shown that the experimentally determined interfacial tension, which decreases from values of 50 mN•m −1 under atmospheric conditions down to 10 mN•m −1 in CO 2 but still above 30 mN•m −1 in CH 4 at 10 MPa, is appropriately reflected by molecular dynamics (MD) simulations. The obtained data are analyzed in view of literature data and by using experimentally determined pressure-dependent densities and solubilities of CH 4 and CO 2 within ionic liquids. The results form part of a database for the ongoing development of MD simulations.

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.

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