  It is shown that porous spherical particles can be obtained via the freezing
of silica nanoparticle aqueous suspensions emulsified in a continuous oil
phase. After two freeze-thaw cycles, nanoparticles turn aggregated into
flocculated objects with microstructure that depends upon emulsion volume
fraction and droplet size. For low volume fractions, regular microspheres are
produced while for large ones, irregular beads with several tens of micrometer
radius are formed. Electronic microscopy, mercury porosimetry and nitrogen
adsorption are used to get insights into these porous particles typical radius,
pore size distribution, surface area and pore network structure. All exhibit
mesopores that result from inter-nanoparticle spacing after flocculation. An
unexpected macroporous domain appears which is not observed when drying
non-emulsified suspensions. This macroporosity is interpreted as the signature
of dendrite formation during the undercooled period, right before freezing
occurs. Beside this additional macroporosity, the protocols presented in this
article constitute also promising emulsion-based routes for porous material
synthesis with original geometry, chemical composition and porosity.
