Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

From Quonset huts to ballerinas

24.01.2006


Princeton scientists solve a nanotech mystery

A team of Princeton researchers has untangled the mystery behind a puzzling phenomenon first observed more than a decade ago in the ultra-small world of nanotechnology.

Why is it, researchers wondered, that tiny aggregates of soap molecules, known as surfactant micelles, congregate as long, low arches resembling Quonset huts once they are placed on a graphite surface?



To fellow scientists and engineers, this question and the researchers’ answer is tantalizing since the discovery gives insight into "guided self-assembly," an important technique in nanotechnology where molecules arrange themselves spontaneously into certain structures. It may also one day lead to valuable technological applications such as the creation of anti-corrosion coatings for metals and bio-medical applications involving plaque formation with proteins.

In a paper appearing in the January 13 issue of Physical Review Letters, a premier physics journal, Dudley Saville, Ilhan Aksay, Roberto Car, and their colleagues explain how they unraveled the mystery.

The scientists discovered they and others had been operating on the flawed assumption that - in response to the texture of the graphite beneath them - surfactant molecules assembled themselves into static ’Quonset Hut’ shapes that stayed put.

Because of new atomic force microscope imaging done by research associate Hannes Schniepp, the Princeton scientists were able to see that the micelle structures were not static but, rather, constantly on the move, building and rebuilding themselves over and over again into the same structures.

To understand what the researchers discovered, it is helpful to switch metaphors. Now, rather than envisioning the molecular assemblies as static Quonset huts, think of them as ensembles of ballerinas in constant motion.

"We spent a year trying to describe why these rods orient themselves on the graphite surface," Saville said. "But it turns out that we had imaged the dancers in freeze-frame. What we did not take into account in our original thinking was that micelles on the surface are in constant rotary motion."

Under most conditions, small particles make tiny random movements known as Brownian motion. Powered by Brownian motion, a single surfactant can be thought of as a dancer spinning about on her own; it is impossible to predict the precise pattern of movement.

What the researchers discovered was that, when molecules assembled into a micelle and the micellar dancer moved on the graphite "stage," it did so in a choreographed fashion.

Something was overriding the rotary Brownian motion. What was it?

"Saville and his coauthors combined theory at the surfactant and micellar scales with a series of careful experiments to resolve the dilemma," said William Russel, the Arthur W. Marks ’19 professor of chemical engineering and dean of the graduate school at Princeton. "Long-range van der Waals forces, which are orientation-dependent, exert a torque on the entire micelle that is strong enough to overcome the randomizing tendency of Brownian motion."

Metaphorical translation: "When micelles appear on the graphite stage, they begin dancing to the music of a van der Waals orchestra," Saville said. The van der Waals interactions – weak links between the electron clouds of the micelles and the graphite below– make the micelles orient in specific directions. Basic work by research associates Je-Luen Li and Jaehun Chun provided a description of the angular variation of the van der Waals interaction and this enabled the group to close the loop.

The scientists said their work opens new horizons to explore. They still have not figured out, for example, how micelles interact with one another on the surface to form large patterned arrays. Or how the micelles disintegrate and reform in the same patterns.

"You need a critical number of dancers for this to happen but we have no idea how many," Aksay said. Moreover, he noted, the researchers can now move on to other interesting questions now that they know that the micelles are dynamic and understand the time frame in which they move. "This opens up the prospect for even more rigorous thinking."

Teresa Riordan | EurekAlert!
Further information:
http://www.princeton.edu

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>