The shape and size control of barium compound nanoparticles (barium chromate, barium sulfate, barium carbonate) was examined using the water-in-oil microemulsion as nanometer-sized reaction medium. The barium compound nanoparticles were synthesized using the microemulsion formed by AOT as an anionic surfactant and iso-octane as an organic solvent. Chromate, sulfate, or carbonate-containing microemulsion solution and Ba(AOT) 2 reverse micelle solution were mixed. After a few days, the morphology of the product material was observed using TEM. Then, bundle of the nanowire, chain structure of the nanorod, superlattice structure of the nanodot, and dispersed nanodot were synthesized by changing material concentration and material molar ratio. It has been shown that the aspect ratio of the generated particles decreased with increase in the anionic ion concentration. In contrast, the aspect ratio did not change even if the barium ion concentration changed. The surfactant AOT has selectively adsorbed on the specific crystal faces and suppressed their crystal growth. And, the generated particles were self-organized by the hydrophobic interaction of hydrophobic group of the AOT molecule adsorbed onto the particle. In conclusion, it was clarified that the supersaturation ratio and the particle–surfactant interaction were important factors for controlling the shape and size of the inorganic nanoparticles.
Colloidal Nanocrystal Shape and Size Control: The Case of Cobalt