Anisotropic Poroelasticity Of Mesoporous Silicon

Confined fluids in mesoporous solids induce deformations of porous matrices. In stiff materials, porous glass and silicon, we show that the pore-load modulus deduced from adsorption and strain measurements on the saturating regime does not depend on the nature of fluid. Thus, the mechanical stress due to the liquid can be described in terms of an isotropic pore pressure derived from macroscopic thermodynamics. Then, we use the framework of anisotropic poroelasticity to get for the first time the whole set of elastic coefficients of porous silicon for various porosities. The elastic constants are in agreement with direct stress-strain tests. We have performed a 2D finite element modeling of porous silicon honeycombs with a geometry transverse to the pore axis as determined by electron microscopy. The calculated moduli are smaller than experimental ones, indicating finite size effect. However, the data cannot be accounted for by a rescaling of Young's modulus of walls, probably due to the lack of invariance along the pore axis.