We developed a miniemulsion-based nanoreactor system, which can allow for morphological tuning of CaCO3 crystals in nanodroplets and their high encapsulation efficiency in polymer particles.
We first obtained nano-sized CaCO3 by using the aqueous nanodroplet as a nanoreactor. In addition, it was found that crystal growth and morphological transformation of CaCO3 from spherical to rod-like crystals were induced by adding 2-hydroxyethyl methacrylate (HEMA) in nanodroplets. Such transformation was also promoted by raising the incubation temperature or increasing the number of nanodroplets in the presence of HEMA. We speculated that crystal growth of CaCO3 crystals was induced by coalescence of nanodroplets and morphological transformation to rodlike shape was undertaken with an assistance of HEMA. In this way, we could tune the shapes of CaCO3 with the well-controlled size and aspect ratio by tuning environments in nanodroplets. Then, subsequent polymerization of HEMA, which was used as a monomer, was carried out for encapsulation of CaCO3 with rod-like morphologies inside polymer nanoparticles. As a result, spherical and spheroidal hybrid nanoparticles, which possessed homogeneity in size and shape, were obtained. Then, by spin-coating of hybrid nanoparticles onto the glass substrate, we could obtain a closely-packed particle monolayer. (C) 2016 Elsevier B.V. All rights reserved.