Porous materials were synthesized by aggregation and consolidation of silica nanoparticles in water, followed by a drying step in which the silicic network experiences capillary forces. The collapse of the obtained structures, measured by small-angle X-ray scattering (SAXS) and mercury porosimetry, provides a characterization of the porous network's resistance towards applied pressure during drying. First, the aggregation process was triggered by the silica nanoparticles's hydrophobization in pure water with alkylalkoxysilanes. Increasing the grafting density allowed going from a dispersed system with a random close packing, to fractal structures whose packing defects are responsible for the remaining porosity. Second, an agglomeration of the pre-formed hydrophobic aggregates, performed by change of pH and ionic strength or by flocculant addition (cations Ca2+, poly(ethylene oxide)), was considered in order to create lower fractal dimension structures. It is shown that the nature of the bonds between the elementary silica particles affects the rearrangements under compression and, consequently, the remaining porosity. It appeared thus essential to include a further consolidation step at basic pH and high temperature, during which the particles are irreversibly fused by a dissolution-reprecipitation mechanism, in order to prevent the collapse under capillary forces during drying. Finally, the silica hydrophobization, initially performed to induce the aggregation in water, provided additional and beneficial damp-proof properties once the materials were dried. The inhibition of capillary condensation started at a grafting density of 1 grafter per nm² for all the considered precursors.
