(339e) Adsorption-Induced Deformation of Hierarchical Mesoporous Structures: Stresses Normal to the Pore Walls and Along the Pore Walls

All porous materials deform upon adsorption of fluids. Similarly to adsorption isotherms, experimentally measured strain isotherms during adsorption (strain as a function of gas pressure) contain a lot of information about the porous material, e.g. its pore size distribution [1] and its elastic properties [2]. There are two approaches to measure the strain isotherms experimentally. The first is in-situ dilatometry, i.e. measurement of the macroscopic elongation of a sample, which works only for monolithic samples [3]. The second is based on in-situ small angle X-ray scattering (SAXS) on ordered porous materials, allowing measurements of the lattice constant as a function of gas pressure [4]. This method only works for sufficiently ordered pore lattices such as ordered mesoporous materials.

Hierarchical silica monoliths with disordered macropores and ordered cylindrical mesopores [5] provide a unique medium, where the adsorption-induced deformation can be studied by means of both aforementioned experimental approaches [6]. While the strain isotherm measured by in-situ SAXS is related to the radial stress normal to the pore walls, the strain isotherm measured by in-situ dilatometry is determined mostly by the axial stress component. The theory of normal adsorption-induced stress in mesoporous materials and corresponding strain has been developed in our earlier work [7]; here we present the extension of this theory for the axial deformation and illustrate it with the experimental data on hierarchical silica-based monoliths.

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