Controlling hydrophobicity of silica nanocapsules prepared from organosilanes

Abstract

Silica nanocapsules with various degrees of surface hydrophobicity were produced by using the inverse miniemulsion technique. Tetraethylorthosilicate was added concurrently with organosilanes containing a variety of hydrophobic ligands (e.g. cyclohexyl and octadecyl). The method is simple and scalable, and yields nano-sized capsules capable of containing hydrophilic components, while using relatively low amounts of surfactants. Commercially used hydrophobic chlorosilanes were demonstrated to be a poor additive for the formation of silica nanocapsules. 29Si solid-state NMR was performed on select silica nanocapsules to show that hydrophobic-alkoxysilanes were incorporated within the silica nanocapsule network. Dynamic light scattering indicated a relative increase in nanocapsule size after being placed in a caustic medium vs. pure silica nanocapsules, and the contact angles of the hydrophobized nanocapsules generally increased with the length of hydrophobic ligand suggesting less interaction of the surface with water. The hydrophobicity of silica nanocapsules was related to their ability to repulse a caustic water environment, thus delaying silica network degradation, which would cause nanocapsule breakage.