Foam bubbles finally brought to order

Foam bubbles finally brought to order

News from Trinity College Dublin announces the first fabrication of the Weaire-Phelan foam, a celebrated theoretical concept not previously realised in the laboratory.

Lord Kelvin would have liked it. When he sat up in bed in 1887 and asked himself - what is the ideal (lowest energy) structure of a liquid foam - he could not have expected this be newsworthy in 2011. But theorists and experimenters have long puzzled over his question, and now the story takes a new turn.

Kelvin’s answer to his challenge (posed for bubbles of equal size) took the form of a simple crystal structure. This was just a guess, but a good one, cleverly worked out by the great man. His generous spirit would have been gratified by the eventual discovery, by Denis Weaire and Robert Phelan, of another structure of lower energy than his. This was computed in 1994 in Trinity College Dublin, with the help of the software of Kenneth Brakke. But they could not make the new foam.

Nevertheless their hypothetical foam attained truly iconic status when used to design the striking Water Cube aquatic centre for the Beijing Olympics. Many millions have admired its elegant framework of steel beams, which follow the pattern of the ideal foam.

Now it exists in reality, thanks to the work of a team led by Ruggero Gabbrielli, in an SFI-funded visiting to Trinity from the University of Trento. Recognising that previous failures could be put down to the shape of the containers used, he designed with Brakke a receptacle whose walls had an intricate form that would encourage and accommodate the Weaire-Phelan bubbles. It was made in Trinity’s CRANN nanotechology centre and proved an instant success when bubbles of the right size were introduced into it.

“Wonderful!” says Weaire, “We shall call this the Italian Job. It opens up a lot of further possibilities.”

Could the new foam be of any practical use? “Not immediately”, says Stefan Hutzler, head of the research group in the School of Physics, “Let’s just admire its extraordinary beauty first… But in solidified form and on various scales, such exotic ordered foams could find applications as chemical filters, heat exchangers and optical components.”

“It’d be interesting to come up with a proof of optimality” Ruggero says “Scientists have been looking at this problem for quite a while, but a rigorous result is still missing”.

The paper reporting the fabrication of the Weaire-Phelan structure was accepted for publication in the time-honoured Philosophical Magazine Letters on the 25th of November 2011. Incidentally, this is the same journal in which both Kelvin (in 1887) and Weaire and Phelan (in 1993) published their work on the structure of ideal foam. To read the paper click here.

ENDS

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