A new in situ setup combining small-angle neutron scattering (SANS) and
dilatometry was used to measure water-adsorption-induced deformation of a
monolithic silica sample with hierarchical porosity. The sample exhibits a
disordered framework consisting of macropores and struts containing twodimensional
hexagonally ordered cylindrical mesopores. The use of an H2O/
D2O water mixture with zero scattering length density as an adsorptive allows a
quantitative determination of the pore lattice strain from the shift of the
corresponding diffraction peak. This radial strut deformation is compared with
the simultaneously measured macroscopic length change of the sample with
dilatometry, and differences between the two quantities are discussed on the
basis of the deformation mechanisms effective at the different length scales. It is
demonstrated that the SANS data also provide a facile way to quantitatively
determine the adsorption isotherm of the material by evaluating the incoherent
scattering contribution of H2O at large scattering vectors.