The formation of gas bubbles — absorbing the heat of vaporization from surrounding environments — is an ordinary phenomenon in a boiling solvent under reflux. Reflux is a widely used technique to supply energy to chemical reactions, which can promote heat transfer and maintain reaction temperature in a narrow range. Solvent bubbles from the constant boiling action continuously mix the reaction solution. And, as Y. Charles Cao and colleagues, University of Florida, USA, report, gas bubbles can also be used to tailor the kinetics of the nucleation and growth of inorganic nanocrystals in a colloidal synthesis.

The researchers conducted a mechanistic study of the synthesis of colloidal iron oxide nanocrystals using gas bubbles generated by boiling solvents or artificial Ar bubbling. They found that bubbling effects take place through absorbing local latent heat released from the exothermic reactions involved in the nucleation and growth of iron oxide nanocrystals.

The gas bubbles display a stronger effect on the nucleation than on the growth, suggesting that both rely on different types of chemical reactions between the iron—oleate decomposition products: the nucleation relies on the strongly exothermic, multiple-bond formation reactions, the growth may primarily depend upon single-bond formation reactions.

The results imply that secondary nucleation depends on the primary nucleation producing a critical amount of nuclei. This suggests a possible route to suppress secondary nucleation.

• Gas-Bubble Effects on the Formation of Colloidal Iron Oxide Nanocrystals,
  Jared Lynch, Jiaqi Zhuang, Tie Wang, Derek LaMontagne, Huimeng Wu, and Y. Charles Cao,
  J. Am. Vhem. Soc. 2011.
  DOI: 10.1021/ja2032597