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Accueil > Evénements > Séminaires > Archives 2015 > Evaporation of Confined
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Séminaire « Matière molle : organisation et dynamique » de l’INSP

Evaporation of Confined Fluids in Porous Materials - Etienne Rolley et Annie Grosman - Lundi 29 juin 2015 à 11 h

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32 - 2e étage, salle 201

Etienne Rolley - LPS-ENS Annie Grosman - INSP

Abstract

For many years, there has been a consensus that evaporation of a liquid confined in a porous matrix is mainly controlled by the geometry of the pores based on the idea that the process occurs via the creation of a vapor path from the surface to the interior of the pores. For porous materials with non connected pores, emptying occurs progressively from the largest to the narrowest pores. For disordered materials with connected pores (i.e. sponge-like), a collective emptying is observed in close analogy with a percolation process. Recent experiments in mesoporous materials have cast some doubt on the generality of such a model and suggest to investigate alternative scenarios based on two fundamental effects : Mechanical coupling. In spite of the non connection between pores, collective effects are observed in porous silicon. We have suggested that the coupling between pores is due to the elastic deformation of the Si walls separating the pores, induced by the fluid adsorption on these walls. As a first step we have performed measurements of both isotherm adsorption and deformation in porous silicon. These coupled measurements will allow us to estimate the surface elastic contribution to the free energy of the solid-fluid system, which is a key parameter in the evaporation process. Cavitation. Another mechanism susceptible to play a role in the emptying is cavitation, that is the thermal nucleation of gas bubbles in the liquid. The use of porous silicon allows us to highlight directly the existence of a cavitation phenomenon by using pores in ink-bottle geometry. First results obtained with liquid nitrogen suggest that the nucleation occurs at the surface of the pore walls (heterogeneous cavitation) rather than in the liquid (homogeneous cavitation).