Preparation of silica capsules via an acid-catalyzed sol–gel process in inverse miniemulsions

Abstract

Silica capsules were prepared via a sol–gel process using tetraethyl orthosilicate (TEOS) in inverse miniemulsions under highly acidic conditions (pH < 2). Formation of silica capsules under acidic conditions proceeded via internal phase separation of silica species in the droplets. This mechanism is different from the well-known interfacial reaction mechanism for most syntheses of silica capsules. The driving force for the formation of capsules was the interaction between silica species and cetyltrimethylammonium bromide (CTAB) as well as between silica species and the hydrophilic block of the block copolymer surfactant, poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO). The effects of synthetic parameters on the particle morphology and size were systematically investigated in terms of the reaction time, amount of TEOS, CTAB, P(E/B)-PEO, and hydrochloric acid concentration, as well as addition of ethanol.