Shape and size control of barium chromate nanoparticles using reverse micelle

The shape and size of barium chromate nanoparticles formed using a water-in-oil microemulsion prepared from the anionic surfactant AOT were examined. As a result, nanowires, nanorods, and nanodots could be synthesized by changing the raw ion concentration and by adding ethanol as a poor solvent. The nanowires and nanorods were self-assembled. It has been shown that the aspect ratio of the generated nanoparticles decreased with increasing chromate ion concentration or due to the addition of ethanol. By contrast, the aspect ratio was almost constant even when the barium ion concentration was changed. The surfactant AOT was selectively adsorbed on the crystal faces of the barium chromate nanoparticles along the a-axis, where it suppressed the growth of their crystal face. Furthermore, the generated nanoparticles were self-assembled through hydrophobic interactions between the surface-anchored AOT molecules. In conclusion, it was clarified that the supersaturation ratio and the particle–surfactant interaction were important factors for controlling the shape and size of these inorganic nanoparticles using the microemulsion method.