Adsorption of n-Pentane on Mesoporous Silica and Adsorbent Deformation

Development of quantitative theory of adsorption-induced deformation is important, e.g., for enhanced coalbed methane recovery by CO2 injection. It is also promising for the interpretation of experimental measurements of elastic properties of porous solids. We study deformation of mesoporous silica by n-pentane adsorption. The shape of experimental strain isotherms for this system differs from the shape predicted by thermodynamic theory of adsorption-induced deformation. We show that this difference can be attributed to the difference of disjoining pressure isotherm, responsible for the solid−fluid interactions. We suggest the disjoining pressure isotherm suitable for n-pentane adsorption on silica and derive the parameters for this isotherm from experimental data of n-pentane adsorption on nonporous silica. We use this isotherm in the formalism of macroscopic theory of adsorption-induced deformation of mesoporous materials, thus extending this theory for the case of weak solid−fluid interactions. We employ the extended theory to calculate solvation pressure and strain isotherms for SBA-15 and MCM-41 silica and compare it with experimental data obtained from small-angle X-ray scattering. Theoretical predictions for MCM-41 are in good agreement with the experiment, but for SBA-15 they are only qualitative. This deviation suggests that the elastic modulus of SBA-15 may change during pore filling

Elastic response of mesoporous silicon to capillary pressures in the pores

We study water adsorption induced deformation of a monolithic, mesoporous silicon membrane traversed by independent channels of amp; 1113088;8 nm diameter. We focus on the elastic constant associated with the Laplace pressure induced deformation of the membrane upon capillary condensation, i.e., the pore load modulus. We perform finite element method FEM simulations of the adsorption induced deformation of hexagonal and square lattices of cylindrical pores representing the mem brane. We find that the pore load modulus weakly depends on the geometrical arrangement of pores, and can be expressed as a function of porosity. We propose an analytical model which relates the pore load modulus to the porosity and to the elastic properties of bulk silicon Young s modulus and Poisson s ratio , and provides an excellent agreement with FEM results. We find good agreement between our experimental data and the predictions of the analytical model, with the Young s modulus of the pore walls slightly lower than the bulk value. This model is applicable to a large class of materials with morphologies similar to mesoporous silicon. Moreover, our findings suggest that liquid condensation experiments allow one to elegantly access the elastic constants of a mesoporous mediu