Mysterious nanobubble burst?

Dec 02, 2008
Mysterious nanobubble burst?
A bubble on the surface (radius R, contact angle θ); at the edges gas flows inwards and achieves an equilibrium with the outflow of gas. This results in a bubble that can remain intact for a long time.

(PhysOrg.com) -- The nanobubbles that develop on submerged surfaces should not really be able to exist. Because of the enormous internal pressure, they should disappear within a short time. Nevertheless, they sometimes last for hours: an unexplained phenomenon.

Professor Detlef Lohse of the University of Twente and his colleague Professor Michael Brenner of Harvard have, however, revealed something of interest. They demonstrated that an equilibrium can develop between the gas that leaves the bubble and the gas that flows into it. It is even possible to calculate the dimensions of a bubble in which this happens. The researchers’ work is being published in Physical Review Letters at the end of November.

The fact that bubbles can develop on a water-repellent surface, submerged in water, had already been demonstrated: these are the round ‘caps’ (see figure) with a diameter of about 100 nanometres and a height of 10 nanometres. The reason they develop is still a mystery but they are nevertheless useful: for example, liquids flow more easily, more rapidly and with less energy consumption along surfaces covered with bubbles. The first techniques for stimulating bubble formation have already been developed as well.

Equilibrium

Nevertheless, it is frustrating that there is still no explanation of how nanobubbles exist. Why should they develop? Small gas bubbles should dissolve rapidly because of the immense internal pressure, the gas flowing out of the bubble. They should disappear within microseconds, whereas measurements have shown that they can last for hours. Lohse and Brenner are searching for the reason why gas flows out of the bubble and, at the same time, inwards. When the two forces are in equilibrium, the bubble can remain intact for much longer than was first thought possible.

According to their theory, the inward flow takes place at the edge of the bubble; in other words, where the edge of a bubble comes in contact with a hydrophobic surface. It is known that, close to a hydrophobic surface, there is a higher concentration of gas molecules: these are then attracted by the surface. If these molecules now flow in via the edge of a bubble, they can reach a state of equilibrium with the molecules that are coming out of the bubble. This equilibrium is actually unstable: according to the second law of thermodynamics, this should only be a transitional phase, implying that the bubbles will dissolve within hours or perhaps days.

The theory, presented in Physical Review Letters, explains the long life of the bubbles. However, the researchers would like to look further into the long-term behaviour of these bubbles. Is the equilibrium unstable after all? Besides this, the new insights help with artificial stimulation of bubbles at the surface, for example, by means of electrolysis.

More information: link.aps.org/abstract/PRL/v101/e214505

Provided by University of Twente, Netherlands

Explore further: Study reveals new characteristics of complex oxide surfaces

add to favorites email to friend print save as pdf

Related Stories

The source of the sky's X-ray glow

Jul 27, 2014

In findings that help astrophysicists understand our corner of the galaxy, an international research team has shown that the soft X-ray glow blanketing the sky comes from both inside and outside the solar system.

What geology has to say about global warming

Jul 14, 2014

Last month I gave a public lecture entitled, "When Maine was California," to an audience in a small town in Maine. It drew parallels between California, today, and Maine, 400 million years ago, when similar ...

Recommended for you

Tough foam from tiny sheets

15 hours ago

Tough, ultralight foam of atom-thick sheets can be made to any size and shape through a chemical process invented at Rice University.

Graphene surfaces on photonic racetracks

Jul 28, 2014

In an article published in Optics Express, scientists from The University of Manchester describe how graphene can be wrapped around a silicon wire, or waveguide, and modify the transmission of light through it.

Simulating the invisible

Jul 28, 2014

Panagiotis Grammatikopoulos in the OIST Nanoparticles by Design Unit simulates the interactions of particles that are too small to see, and too complicated to visualize. In order to study the particles' behavior, he uses ...

Building 'invisible' materials with light

Jul 28, 2014

A new method of building materials using light, developed by researchers at the University of Cambridge, could one day enable technologies that are often considered the realm of science fiction, such as invisibility ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

guiding_light
not rated yet Dec 04, 2008
You know what I'm thinking; what does this mean for those hydrophobic materials used for immersion lithography?