A research team in from Aix-Marseille University in France has immobilized a microbubble underwater. The accomplishment seems to contradict Archimedes’ principle on the buoyancy of force that would normally push it to the surface. The researchers' find could have application in medicine, the nuclear industry, or micromanipulation technology.

Controlling microbubbles is critical to applications in medicine, including as ultrasound contrast agents, for breaking up blood clots, and for gas embolotherapy, which is the intentional blocking of an artery to prevent excessive blood loss. Controlling microbubbles is also important in the nuclear industry, where microbubbles in liquid sodium coolant can cause problems.

Microbubble immobilized in solution above the apex of the nanoelectrode.  Image source: CINaM-CNRS Aix-Marseille UniversityMicrobubble immobilized in solution above the apex of the nanoelectrode. Image source: CINaM-CNRS Aix-Marseille UniversityBubbles are common in nature, but it is not easy to control their diameter, position, or time of formation. Previous work by the French research team explored how to control hydrogen and oxygen gas bubbles that are formed by the breakdown of water using electricity. They showed that if one of the electrodes is tip-shaped—with a curvature radius at its apex ranging from 1 nanometer to 1 micrometer—and an alternating electric current with definite values of amplitude and frequency was used, microbubbles could be produced at a single point at the apex of the nanoelectrode.

In their most recent work, the team produced a microbubble (at the apex of the nanoelectrode) then immobilized it by rapidly increasing the frequency of the electric current. They found that no matter which direction the electrode was moved, the bubble remained above and at the same distance from the electrode.

The scientists propose that the hydrogen or oxygen molecules enter the immobilized bubble through the lower surface and exit the bubble through the upper surface. The gas molecules are produced at a single point at the apex of the nanoelectrode.

Juan Olives, a member of the research team, says that the greatest surprise in the findings was that, although nothing appears to be moving during the experiment, all is moving in an apparent steady state. Hydrogen and oxygen molecules are continually produced at the apex of the nanoelectrode; they move in the solution and in the bubble; they enter and leave the bubble; and there is a convection velocity in the solution and in the bubble. Everything moves except the surface of the bubble, he says.

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