Foam bubbles finally brought to order

In 1994, Denis Weaire and Robert Phelan of Trinity College Dublin’s School of Physics made a landmark discovery in foam physics, and created a new ideal structure of foam.  It is the most efficient way to partition space into equal volume cells while minimising surface area – something soap bubbles strive to do in nature.   Their geometry of soap bubbles improved on a previous principle devised by the physicist, Lord Kelvin a century ago.

The Weaire-Phelan structure consists of two kinds of polyhedral bubbles with twelve and fourteen sides respectively. The structure can be cut along planes, showing the existence of layers of bubbles. Since its introduction in 1994 it has played an important role in theory and simulation of foams, for example in the study of elastic properties.

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The structure went on to inspire the design of the 2008 Olympic Games' iconic building, the Water Cube in the National Aquatic Center in Beijing.  Many millions have admired its elegant framework of steel beams, which follow the pattern of the ideal foam.

The physicists have now gone a step further and this month succeeded in turning the mathematical concept into real foam.

Now it exists in reality, thanks to the work of a team led by Dr. Ruggero Gabbrielli, from the University of Trento, in an SFI-funded visit to Trinity College.  Back in 1994 while the concept was computed, with the help of the software by Kenneth Brakke, they were unable to fabricate the new foam.

Acknowledging that the previous failures could be put down to the shape of the containers used, Gabbrielli along with Brakke designed a receptacle whose walls had an intricate form that would encourage and accommodate the Weaire-Phelan bubbles.  It was made in Trinity’s nanoscience institute, CRANN  and proved an instant success when bubbles of the right size were introduced into it.

“Wonderful!” says Weaire, now an Emeritus Professor in the School of Physics. “We shall call this the Italian Job.  It opens up a lot of further possibilities.”

In response to whether the new foam could be of any practical use: “Not immediately”, says Professor Stefan Hutzler, Head of the Foams and Complex Systems 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-honored science journal Philosophical Magazine Letters on the 25th of November 2011.  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.

Provided by Trinity College Dublin (news : web)

Clay-armored bubbles may have formed first protocells: Minerals could have played a key role in the origins of life

ScienceDaily (Feb. 7, 2011) — A team of applied physicists at Harvard's School of Engineering and Applied Sciences (SEAS), Princeton, and Brandeis have demonstrated the formation of semipermeable vesicles from inorganic clay.

The research, published online in the journal Soft Matter, shows that clay vesicles provide an ideal container for the compartmentalization of complex organic molecules.

The authors say the discovery opens the possibility that primitive cells might have formed inside inorganic clay microcompartments.

"A lot of work, dating back several decades, explores the role of air bubbles in concentrating molecules and nanoparticles to allow interesting chemistry to occur," says lead author Anand Bala Subramaniam, a doctoral candidate at SEAS.

"We have now provided a complete physical mechanism for the transition from a two-phase clay-air bubble system, which precludes any aqueous-phase chemistry, to a single aqueous-phase clay vesicle system," Subramaniam says, "creating a semipermeable vesicle from materials that are readily available in the environment."

"Clay-armored bubbles" form naturally when platelike particles of montmorillonite collect on the outer surface of air bubbles under water.

When the clay bubbles come into contact with simple organic liquids like ethanol and methanol, which have a lower surface tension than water, the liquid wets the overlapping plates. As the inner surface of the clay shell becomes wet, the disturbed air bubble inside dissolves.

The resulting clay vesicle is a strong, spherical shell that creates a physical boundary between the water inside and the water outside. The translucent, cell-like vesicles are robust enough to protect their contents in a dynamic, aquatic environment such as the ocean.

Microscopic pores in the vesicle walls create a semipermeable membrane that allows chemical building blocks to enter the "cell," while preventing larger structures from leaving.

Scientists have studied montmorillonite, an abundant clay, for hundreds of years, and the mineral is known to serve as a chemical catalyst, encouraging lipids to form membranes and single nucleotides to join into strands of RNA.

Because liposomes and RNA would have been essential precursors to primordial life, Subramaniam and his coauthors suggest that the pores in the clay vesicles could do double duty as both selective entry points and catalytic sites.

"The conclusion here is that small fatty acid molecules go in and self-assemble into larger structures, and then they can't come out," says principal investigator Howard A. Stone, the Dixon Professor in Mechanical and Aerospace Engineering at Princeton, and a former Harvard faculty member. "If there is a benefit to being protected in a clay vesicle, this is a natural way to favor and select for molecules that can self-organize."

Future research will explore the physical interactions between the platelike clay particles, and between the liquids and the clay. The researchers are also interested to see whether these clay vesicles can, indeed, be found in the natural environment today.

"Whether clay vesicles could have played a significant role in the origins of life is of course unknown," says Subramaniam, "but the fact that they are so robust, along with the well-known catalytic properties of clay, suggests that they may have had some part to play."

Subramaniam and Stone's coauthors include Jiandi Wan, of Princeton University, and Arvind Gopinath, of Brandeis University.

The research was funded by the Harvard Materials Research Science and Engineering Center and supported by the Harvard Center for Brain Science Imaging Facility.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Harvard University, via EurekAlert!, a service of AAAS.

Journal Reference:

Anand Bala Subramaniam, Jiandi Wan, Arvind Gopinath, Howard A. Stone. Semi-permeable vesicles composed of natural clay. Soft Matter, 2011; DOI: 10.1039/C0SM01354D