Effect of pore size distribution on sorption-induced deformation of porous materials: A theoretical study

Abstract

Porous materials exhibit complex deformation when interacting with adsorbates in the environment. Depending on the size and shape of individual pores, interactions between solid and adsorbates can give rise to several pore-scale forces that impact the overall adsorption and strain isotherms. Accurate prediction of the adsorption-deformation behavior of a porous material would benefit from the consideration of its pore network characteristics described by the pore size distribution (PSD). This paper presents a theoretical investigation on how the pore size distribution can affect the sorption-induced deformation of micro/meso/macro porous solids. The recently developed surface poromechanics theory is generalized to account for the information of arbitrary pore size distributions. The adsorptive energetics of a generic pore network is statistically upscaled from the solid-adsorbate interaction in a single slit pore geometry, which is then infused into the thermodynamics of a deformable body. The theory is first validated against the experimental data on microporous carbon interacting with nitrogen gas. Then the same parameter set is used to study the effects of pore size on the adsorption and strain isotherms of porous materials. By only varying the input PSDs, a variety of adsorption-deformation behaviors that are commonly observed from experiments is reproduced by the model. Conclusions are drawn from this analysis regarding the relative dominance of different pore-scale forces at varying pore size ranges, and the circumstances where simplified representation of the pore network can be acceptable.