Morphology and size control of nanocalcium carbonate crystallised in reverse micelle system with cationic surfactant cetyltrimethylammonium bromide

The influence of ω₀, the mole ratio of water-to-surfactant content ([H₂O]/[surfactant]), on the crystal size of calcium carbonate (CaCO₃) produced by reaction crystallisation in microemulsion systems was investigated. Crystallisation was induced by the reaction between an aqueous solution of sodium carbonate and water in oil micellar solutions of calcium chloride stabilised by cationic surfactant cetyltrimethylammonium bromide and cosurfactant n-butylalcohol. The X-ray diffraction results showed that calcite is the main state of CaCO₃ crystal when ω₀>30, but because of the stable reverse micelles system, vaterite was the predominant crystal form when ω₀<; 30. Scanning electron microscopy and high-resolution transmission electron microscopy results showed spherical CaCO₃ nanoparticles obtained with narrow size distribution, and with the ratio of water-to-surfactant increasing from 3.40 to 22.63, the particles size increased from 15 to 70 nm. The influence of ω₀ on the crystal size and morphology of CaCO₃ was very clear.