Application of Derjaguin-Broekhoff-De Boer Theory and Molecular Simulation for Calculation of Solvation Pressure in Spherical Mesopores

Adsorption of fluids in porous structure takes place due to the intermolecular interactions between solid surface and adsorbate. During this process, the adsorbate confined in pore exhibits high “solvation” pressure on the pore walls and causes the deformation of porous materials [1]. The high pressure in the pores have additional effects other than mechanical strains, in particular, some of the high-pressure chemical reactions take place in the pores at the moderate gas pressures [2,3], or the compressibility of fluids in pores changes [4]. Here we focus on solvation pressure in model silica pores of spherical shape induced by the adsorption of nitrogen.

We use the thermodynamic model for calculating solvation pressure from adsorption isotherms, applied before for various microporous materials [5,6] and mesoporous materials with cylindrical pores [7]. We apply it for spherical mesopores using the adsorption isotherms predicted from the macroscopic Derjaguin-Broekhoff-de Boer (DBdB) theory [8-10] and grand canonical molecular simulations. We show that both approaches give consistent results, which are also typical for the solvation pressure in mesoporous materials, yet noticeably differ from the results for cylindrical pore geometry [7]. Furthermore, we show that the dependence of the solvation pressure on the reciprocal pore size can be used for the calculation of the solid-liquid surface energy. Finally, we relate the calculated solvation pressures to the compressibility of liquid nitrogen in spherical confinement and found that the departure of the compressibility from the bulk value is consistent with the calculated values of solvation pressures.

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