Nav: Home

Fluid dynamics works on nanoscale in real world

February 23, 2007

In 2000, Georgia Tech researchers showed that fluid dynamics theory could be modified to work on the nanoscale, albeit in a vacuum. Now, seven years later they've shown that it can be modified to work in the real world, too - that is, outside of a vacuum. The results appear in the February 9 issue of Physical Review Letters (PRL).

Understanding the motion of fluids is the basis for a tremendous amount of engineering and technology in contemporary life. Planes fly and ships sail because scientists understand the rules of how fluids like water and air behave under varying conditions. The mathematical principle that describe these rules wave put forth more than 100 years ago and are known as the Navier-Stokes equations. They are well-known and understood by any scientist or student in the field. But now that researchers are delving into the realm of the small, an important question arisen: namely, how do these rules work when fluids and flows are measured on the nanoscale? Do the same rules apply or, given that the behavior of materials in this size regime often has little to do with their macro-sized cousins, are there new rules to be discovered?

It's well-known that small systems are influenced by randomness and noise more than large systems. Because of this, Georgia Tech physicist Uzi Landman reasoned that modifying the Navier-Stokes equations to include stochastic elements - that is give the probability that an event will occur - would allow them to accurately describe the behavior of liquids in the nanoscale regime.

Writing in the August 18, 2000, issue of Science, Landman and post doctoral fellow Michael Moseler used computer simulation experiments to show that the stochastic Navier-Stokes formulation does work for fluid nanojets and nanobridges in a vacuum. The theoretical predictions of this early work have been confirmed experimentally by a team of European scientists (see the December 13, 2006, issue of Physical Review Letters). Now, Landman and graduate student Wei Kang have discovered that by further modifying the Moseler-Landman stochastic Navier-Stokes equations, they can accurately describe this behavior in a realistic non-vacuous environment.

"There was a strong opinion that fluid dynamics theory would stop being valid for small systems," said Landman, director of the Center for Computational Materials Science, Regents' and Institute professor, and Callaway chair of physics at the Georgia Institute of Technology. "It was thought that all you could do was perform extensive, as well as expensive, molecular dynamic simulations or experiments, and that continuum fluid dynamics theory could not be applied to explain the behavior of such small systems."

The benefit of the new formulations is that these equations can be solved with relative ease in minutes, in comparison to the days and weeks that it takes to simulate fluid nano structures, which can contain as many as several million molecules. Equally difficult, and sometimes even harder, are laboratory experiments on fluids in this regime of reduced dimensions.

In this study, Landman and Wei simulated a liquid propane bridge, which is a slender fluid structure connecting two larger bodies of liquid, much like a liquid channel connecting two rain puddles. The bridge was six nanometers in diameter and 24 nanometers long. The object was to study how the bridge collapses.

In the study performed in 2000, Landman simulated a bridge in a vacuum. The bridge broke in a symmetrical fashion, pinching in the middle, with two cones on each side. This time, the simulation focused on a model with a nitrogen gas environment surrounding the bridge at different gas pressures.

When the gas pressure was low (under 2 atmospheres of nitrogen), the breaking occurred in much the same way that it did in the previous vacuum computer experiment. But when the pressure was sufficiently high (above 3.5 atmospheres), 50 percent of the time the bridge broke in a different way. Under high pressure, the bridge tended to create a long thread and break asymmetrically on one side or the other of the thread instead of in the middle. Until now, such asymmetric long-thread collapse configuration has been discussed only for macroscopically large liquid bridges and jets.

Analyzing the data showed that the asymmetric breakup of the nanobridge in a gaseous environment relates to molecular evaporation and condensation processes and their dependence on the curvature of the shape profile of the nanobridge.

"If the bridge is in a vacuum, molecules evaporating from the bridge are sucked away and do not come back" said Landman. "But if there are gas molecules surrounding the bridge, some of the molecules that evaporate will collide with the gas, and due to these collisions the scattered molecules may change direction and come back to the nanobridge and condense on it."

As they return they may fill in spaces where other atoms have evaporated. In other words, the evaporation-condensation processes serve to redistribute the liquid propane along the nanobridge, resulting in an asymmetrical shape of the breakage. The higher the pressure is surrounding the bridge, the higher the probability that the evaporating atoms will collide with the gas and condense on the nanobridge. Landman and Wei have shown that these microscopic processes can be included in the stochastic hydrodynamic Navier-Stokes equations, and that the newly modified equations reproduce faithfully the results of their atomistic molecular dynamics experiments.

"Knowing that the hydrodynamic theory, that is the basis of venerable technologies around us, can be extended to the nanoscale is fundamentally significant, and a big relief" said Landman. "Particularly so, now that we have been able to use it to describe the behavior of nanofluids in a non-vacuous environment - since we expect that this is where most future applications would occur."

Georgia Institute of Technology

Related Nanoscale Articles:

Discovery will allow more sophisticated work at nanoscale
The movement of fluids through small capillaries and channels is crucial for processes ranging from blood flow through the brain to power generation and electronic cooling systems, but that movement often stops when the channel is smaller than 10 nanometers.
Valley-Hall nanoscale lasers
Topological photonics allows the creation of new states of light.
Dynamics of DNA replication revealed at the nanoscale
Using super-resolution technology a University of Technology Sydney led team has directly visualised the process of DNA replication in single human cells.
House cleaning on the nanoscale
A team of scientists at Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) has developed a novel mechanical cleaning method for surfaces on the nanoscale.
As electronics shrink to nanoscale, will they still be good as gold?
As circuit interconnects shrink to nanoscale, will the pressure caused by thermal expansion when current flows through wires cause gold to behave more like a liquid than a solid -- making nanoelectronics unreliable?
A joint venture at the nanoscale
Scientists at Argonne National Laboratory report fabricating and testing a superconducting nanowire device applicable to high-speed photon counting.
Bending diamond at the nanoscale
A team of Australian scientists has discovered diamond can be bent and deformed, at the nanoscale at least.
Creating a nanoscale on-off switch for heat
Researchers create a polymer thermal regulator that can quickly transform from a conductor to an insulator, and back again.
Magnetic tuning at the nanoscale
Physicists from the German research center Helmholtz-Zentrum Dresden-Rossendorf (HZDR) are working to produce engineered magnetic nanostructures and to tailor material properties at the nanoscale.
Scientists can now control thermal profiles at the nanoscale
Scientists have designed and tested an experimental system that uses a near-infrared laser to actively heat two gold nanorod antennae to different temperatures.
More Nanoscale News and Nanoscale Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at     You can read The Transition Integrity Project's report here.