"Extraordinarily fast transport of water in carbon nanotubes has generally been attributed to the smoothness of the nanotube walls and their hydrophobic, or water-hating surfaces," said Narayana R. Aluru, a Willett Faculty Scholar and a professor of mechanical science and engineering at the U. of I.
"We can now show that the fast transport can be enhanced by orienting water molecules in a nanotube," Aluru said. "Orientation can give rise to a coupling between the water molecules' rotational and translational motions, resulting in a helical, screw-type motion through the nanotube," Aluru said.
Using molecular dynamics simulations, Aluru and graduate student Sony Joseph examined the physical mechanism behind orientation-driven rapid transport. For the simulations, the system consisted of water molecules in a 9.83 nanometer long nanotube, connected to a bath at each end. Nanotubes of two diameters (0.78 nanometers and 1.25 nanometers) were used. Aluru and Joseph reported their findings in the journal Physical Review Letters.
For very small nanotubes, water molecules fill the nanotube in single-file fashion, and orient in one direction as a result of confinement effects. This orientation produces water transport in one direction. However, the water molecules can flip their orientations collectively at intervals, reversing the flow and resulting in no net transport.
In bigger nanotubes, water molecules are not oriented in any particular direction, again resulting in no transport.
Water is a polar molecule consisting of two hydrogen atoms and one oxygen atom. Although its net charge is zero, the molecule has a positive side (hydrogen) and a negative side (oxygen). This polarity causes the molecule to orient in a particular direction when in the presence of an electric field.
Creating and maintaining that orientation, either by directly applying an electric field or by attaching chemical functional groups at the ends of the nanotubes, produces rapid transport, the researchers report.
"The molecular mechanism governing the relationship between orientation and flow had not been known," Aluru said. "The coupling occurs between the rotation of one molecule and the translation of its neighboring molecules. This coupling moves water through the nanotube in a helical, screw-like fashion."
In addition to explaining recent experimental results obtained by other groups, the researchers' findings also describe a physical mechanism that could be used to pump water through nanotube membranes in next-generation nanofluidic devices.
James E. Kloeppel | EurekAlert!
NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center
Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses