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Porous materials: persistent capillarity at the molecular scale

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(Translated from l’INC, CNRS)
Because of their ability to capture and trap molecules, microporous solids-whose pores have diameters on the order of nanometres-are at the heart of many applications in the fields of health, energy and the environment. For example, they are used as molecular sieves, ion exchangers or catalysts. However, the rationalization of fluid behavior within these materials remains a challenge because capillary models validated for larger pore sizes are no longer relevant in such extreme containment situations. Thus, the phenomenon of macroscopic capillary condensation, which corresponds to a discontinuous and possibly irreversible filling of the porosity, is no longer observed in microporous media because it has been replaced by a continuous and reversible mechanism.

Using molecular simulations and experimental measurements, scientists from the Mulhouse Institute of Materials Science (CNRS/University of Haute Alsace) and the Interdisciplinary Physics Laboratory (CNRS/University Grenoble Alpes) have studied the containment of different fluids in zeolite-type microporous materials, which are among the most widely used microporous materials. They show that capillarity and associated macroscopic concepts remain relevant when porosity dimensions are reduced to the critical nanometre threshold. By developing a theoretical model to account for their data, they obtain a reliable and rapid estimate of the filling conditions of a fluid/material couple based on simple parameters such as pore size, surface tension and fluid density. A simple way to match the best material to its optimal use.

View online : Irena Deroche, Jean Daou, Cyril Picard, Benoit Coasne, Reminiscent capillarity in subnanopores Nature Communications