Bio-inspired nanoreactor based on a miniemulsion system to create organic–inorganic hybrid nanoparticles and nanofilms

Abstract

We developed a novel route to control both mineralization and polymerization inside a nanoreactor based on a miniemulsion system to create organic–inorganic hybrid nanomaterials with diverse structures and morphologies. Nanodroplets of calcium nitrate (Ca(NO₃)₂)/monomer and nanodroplets of sodium carbonate (Na₂CO₃) were separately prepared and suspended in the oil phase. They were mixed through the fusion and fission process triggered by ultrasonication to precipitate a biomineral only inside the nanodroplets. In the presence of monomer, 2-hydroxyethyl methacrylate (HEMA), we could obtain unique structures of nano-sized CaCO₃ particles, which were crystalline with spherical or rod-like shapes or amorphous. By subsequent polymerization, we could encapsulate nano-CaCO₃ inside the polymeric nanoparticles at a desired stage of crystal growth. The preincubation period for CaCO₃ nucleation and growth and the polymerization rate were important factors to manipulate the structures and polymorphs of nano-CaCO₃ inside the hybrid nanoparticles, owing to inhibition of crystal growth and transformation by polymerization of HEMA. Also, the growth of rod-like CaCO₃ inside the nanoparticles led to formation of spheroidal hybrid nanoparticles. By using hybrid nanoparticles as building blocks, we could produce nanofilms containing nano-CaCO₃ with a variety of sizes and structures. Crystal transformation of amorphous CaCO₃ was induced inside the nanofilm by increasing the temperature to above the T_g of PHEMA.