Enhanced Continuum Poromechanics to Account for Adsorption Induced Swelling of Saturated Isotropic Nanoporous Materials: Fid-Bau Portal

Enhanced Continuum Poromechanics to Account for Adsorption Induced Swelling of Saturated Isotropic Nanoporous Materials

Vermorel, Romain / Pijaudier-Cabot, Gilles

Poromechanics offers a consistent theoretical framework for describing the mechanical response of porous solids fully or partially saturated with a fluid phase. When dealing with fully saturated nanoporous materials, which exhibit pores of the nanometer size, effects due to adsorption and confinement of the fluid molecules in the smallest pores must be accounted for. From the mechanical point of view, these phenomena result into volumetric deformations of the porous solid, the so-called "swelling" phenomenon. The present work investigates how the poromechanical theory may be refined in order to describe such adsorption and confinement induced effects in nanoporous solids. The new formulation introduces an effective pore pressure, defined as a thermodynamic variable at the representative volume element scale (mesoscale), which is related to the overall mechanical work of the confined fluid. Accounting for the thermodynamic equilibrium of the system, we demonstrate that the effective pore pressure depends on measurable variables, such as the bulk fluid pressure, the temperature and the total and excess adsorbed mass of fluid. As an illustrating example, we compute the strains in the case of the methane and carbon dioxide sorption-induced swelling of an activated carbon. The fits provide a good agreement with material parameters (apparent and matrix compression moduli, porosity) available in the literature, with a close agreement with experimental data.