Hybrid mesoporous microspheres from aqueous droplets containing a silica nanoparticle–polymer network in a W/O suspension

Abstract

An aqueous dispersion of a reactive copolymer with trimethoxysilyl side chains and silica nanoparticles (SiPs) was added to silicone oil containing 3-aminopropyltrimethoxysilane (APS). The mixture was vigorously stirred for several hours. Consequently, spherical water droplets were formed through the condensation reactions of the copolymer and SiPs as well as APS, which was relocated from the oil phase to the aqueous phase. During the reaction, water was consumed by hydrolysis of the methoxysilyl groups of APS and the droplets gradually solidified. The particulate formation was continuously investigated through optical microscopy. The obtained dried particles were characterized thoroughly using scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), elemental analysis, ²⁹Si cross-polarization/magic angle spinning nuclear magnetic resonance (²⁹Si CP/MAS NMR) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. The results reveal that these microspheres possess a good compressive strength as APS was successfully incorporated to form Si–O–Si linkages with the copolymer and SiPs to connect the components inside the droplets. The amino functional groups in APS also act to avoid coagulation of the prepared microspheres. Furthermore, it was found that mesoporous silica microspheres embedded with nano-sized silica can also be prepared by calcination of the hybrid microspheres without any fracture. The FE-SEM image of the inner surface of the charred particles shows a uniform distribution of the SiPs and thus confirmed the appropriate morphology of the microspheres.