Preparation of colloidal monodisperse hollow organosiloxane-based nanoparticles with a double mesoporous shell

Hollow siloxane-based nanoparticles (HSNs) have attracted significant attention because of many potential applications. The interior and exterior properties of HSNs can be varied by forming double shells with different compositions, which leads to new functionalities. In this study, we prepared colloidal monodisperse HSNs (smaller than 50 nm in diameter) with a double mesoporous shell by the stepwise addition of two different bridged organoalkoxysilanes [(EtO)₃Si-C₂H₄-Si(OEt)₃ (BTEE1) and (EtO)₃Si-C₂H₂-Si(OEt)₃ (BTEE2)] to a dispersion of colloidal silica nanoparticles (ca. 20 nm in diameter) in the presence of surfactants. The hollow structure was formed by dissolution-redeposition of the silica core during the formation of an organosiloxane shell. Upon addition of BTEE1 in the first step, core-shell structure was formed. Subsequent addition of BTEE2 led to the formation of mesoporous HSNs composed of an inner shell containing ethylene (-CH₂-CH₂-) groups and an outer shell containing ethenylene (-CH=CH-) groups. Suppression of the diffusion of the second organosilane species into the inner region of HSNs was critical for the formation of the double shell. The ethenylene groups in the outer shell allowed for chemical modification by thiol-ene reaction while maintaining the hollow inner space of the HSNs, which will lead to the application of HSNs in various fields.