Self-Stirring Liquids Now Possible

Chemists have recently made a discovery that could change the way chemical reactions are approached forever. They have determined that, while mixing a reaction has the ability to promote it, the opposite is also true. In other words, putting the right mix of elements together can trigger a stirring reaction inside the liquids, without external intervention from the researchers, or from specialized machines. A paper on this issue, appearing in the January 29 issue of the respected scientific journal Physical Review Letters, argues that certain chemical reactions can cause fluid flows, Wired reports.

Anne De Wit, a scientist at the Universite Libre de Bruxelles, in Belgium, and also a coauthor of the investigation, says that the work touches fields ranging from astronomy to geology and medicine. For example, the new knowledge could shed an entirely different light on the way chemical reactions and nuclear fusion takes place inside stars, or on how carbon deep in our planet's mantle reacts and changes when it encounters water under very high pressures. The research set out from a curiosity De Wit and her team had, of learning what happens in terms a fluid flow to a reaction that is not stirred.

The team therefore looked at a rather basic chemical reaction, the neutralization process that occurs between hydrochloric acid (HCl) and sodium hydroxide (NaOH). Usually, this reaction is enhanced and promoted through stirring, but the group refrained from doing so. In a container, they injected the hydroxide first, as the material has a greater density than the acid. The hydrochloric acid was then added on top of the NaOH. The team observed that, at the line where the two materials met, the common byproducts of the reaction – water and salt – formed. As this happened, something peculiar was observed.

The salty solution tended to rise through the lower-density acid, forming tendrils as it did so. These structures began to immediately mix the solution above the reaction line, just like stirring would. The same effect was however not observed below the line, because the higher density of the hydroxide prevented tendrils from mixing the stuff. “These kinds of beautiful patterns can be observed with very well-known reactions. This is quite fascinating for someone who’s done this reaction hundreds of times,” adds researcher Christophe Almarcha, also a coauthor of the paper.





Video: a video showing the self-stirring reaction the Belgian team demonstrated
Credit: C. Almarcha/Université Libre de Bruxelles