In-situ small-angle neutron scattering investigation of adsorption-induced deformation in silica with hierarchical porosity

The water adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in-situ small-angle neutron scattering (SANS) and in-situ dilatometry. The monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally-ordered cylindrical mesopores, and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in the SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A H2O/D2O mixture with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in-situ dilatometry result from a combination of axial and radial mesopore deformatio...