Controlled formation of macroporous or hollow silica particles in non-aqueous silicone dispersions

The formation of silica particles by sol–gel processes from alkoxysilane precursors normally requires an aqueous environment. This study demonstrates that optionally macroporous or hollow silica particles can be formed from Si(OEt)4 within silicone oil: water, a key element in the process, is provided only from moisture in the atmosphere. Particles grow in or around a non-aqueous dispersion of poly(ethylene glycol) droplets in the silicone, which may be an oil or a curing elastomer. The structures of both the silica and silicone elastomer are established in a one pot/one step methodology. Control of the silica particle morphology is provided simply by choice of the amine catalyst, benzylamine or dodecylamine: benzylamine leads to open, macroporous monolithic particulate structures, where the particles are also mesoporous, while dodecylamine gives hollow particles with highly condensed shells. These differences arise from the relative abilities of the two catalysts to partition between the hydrophilic/hydrophobic silicone/poly(ethylene glycol) media. The two morphologies release the surrogate drug fluorescein with different profiles.