Properties of 'confined' water within single-walled carbon nanotube pores clarified

ScienceDaily (June 23, 2011) — Water and ice may not be among the first things that come to mind when you think about single-walled carbon nanotubes (SWCNTs), but a Japan-based research team hoping to get a clearer understanding of the phase behavior of confined water in the cylindrical pores of carbon nanotubes zeroed in on confined water's properties and made some surprising discoveries.

The team, from Tokyo Metropolitan University, Nagoya University, Japan Science and Technology Agency, and National Institute of Advanced Industrial Science and Technology, describes their findings in the American Institute of Physics' Journal of Chemical Physics.

Although carbon nanotubes consist of hydrophobic (water repelling) graphene sheets, experimental studies on SWCNTs show that water can indeed be confined in open-ended carbon nanotubes.

This discovery gives us a deeper understanding of the properties of nanoconfined water within the pores of SWCNTs, which is a key to the future of nanoscience. It's anticipated that nanoconfined water within carbon nanotubes can open the door to the development of a variety of nifty new nanothings -- nanofiltration systems, molecular nanovalves, molecular water pumps, nanoscale power cells, and even nanoscale ferroelectric devices.

"When materials are confined at the atomic scale they exhibit unusual properties not otherwise observed, due to the so-called 'nanoconfinement effect.' In geology, for example, nanoconfined water provides the driving force for frost heaves in soil, and also for the swelling of clay minerals," explains Yutaka Maniwa, a professor in the Department of Physics at Tokyo Metropolitan University. "We experimentally studied this type of effect for water using SWCNTs."

Water within SWCNTs in the range of 1.68 to 2.40 nanometers undergoes a wet-dry type of transition when temperature is decreased. And the team discovered that when SWCNTs are extremely narrow, the water inside forms tubule ices that are quite different from any bulk ices known so far. Strikingly, their melting point rises as the SWCNT diameter decreases -- contrary to that of bulk water inside a large-diameter capillary. In fact, tubule ice occurred even at room temperature inside SWCNTs.

"We extended our studies to the larger diameter SWCNTs up to 2.40 nanometers and successfully proposed a global phase behavior of water," says Maniwa. "This phase diagram (see image) covers a crossover from microscopic to macroscopic regions. In the macroscopic region, a novel wet-dry transition was newly explored at low temperature."

Results such as these contribute to a greater understanding of fundamental science because nanoconfined water exists and plays a vital role everywhere on Earth -- including our bodies. "Understanding the nanoconfined effect on the properties of materials is also crucial to develop new devices, such as proton-conducting membranes and nanofiltration," Maniwa notes.

Next up, the team plans to investigate the physical properties of confined water discovered so far inside SWCNTs (such as dielectricity and proton conduction). They will pursue this to obtain a better understanding of the molecular structure and transport properties in biological systems.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New properties of supercooled confined water discovered

ScienceDaily (May 12, 2011) — A study led by the UB researcher Giancarlo Franzese and published in the journal Physical Review Letters suggests that hydrophobic nanoconfinement can alter the thermodynamics of water at supercool temperatures. These findings may have important applications in fields related to conservation at cryogenic temperatures (around -100 ºC) -- for example, in the preservation of stem cells, blood and food products.

The team behind the study, led by Giancarlo Franzese from the UB's Department of Fundamental Physics, included researchers from Boston University and TU Berlin.

Water exhibits atypical fluid behaviour. One of its unique characteristics is the increase in heat capacity as water cools, an anomaly that enables us to regulate our body temperature. When water is supercooled -- that is, when it is in liquid state at a temperature below its melting point -- the range of anomalies expands. This irregular behaviour has generated fierce scientific debate over the last twenty years and could hold the key to understanding why water is so different to other liquids and why it is so important for biological organisms.

From a technical perspective, it is difficult to observe supercooled water directly and many researchers opt to use nanoconfinement. In this study, the team used Monte Carlo simulations to study a layer of water only one nanometre high -- approximately equivalent to the diameter of three water molecules -- confined between two hydrophobic plates. Hydrophobic nanoparticles were then added to the water layer in random positions to generate nanochannels or variable size.

This process led to a strong decrease in thermodynamic fluctuations, reflected in compressibility, thermal expansion coefficient and specific heat. The observed decrease occurred at all pressures tested, and at pressures in the region of 180 MPa fluctuations dropped by almost 99% for a concentration in nanoparticles of 25% by volume. The reduction was found to be as high as 90% even at a particle concentration ten times lower.

According to Giancarlo Franzese, the results show that the thermodynamic behaviour of water confined in hydrophobic nanochannels is very different to that of unconfined water, even allowing for the possible presence of more than one liquid phase within the range of temperatures and pressures tested.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Universidad de Barcelona, via AlphaGalileo.

Journal Reference:

Elena Strekalova, Marco Mazza, H. Stanley, Giancarlo Franzese. Large Decrease of Fluctuations for Supercooled Water in Hydrophobic Nanoconfinement. Physical Review Letters, 2011; 106 (14) DOI: 10.1103/PhysRevLett.106.145701

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Mixing fluids efficiently in confined spaces: Let the fingers do the working

ScienceDaily (May 13, 2011) — Getting two fluids to mix in small or confined spaces is a big problem in many industries where, for instance, the introduction of one fluid can help extract another -- like water pumped underground can release oil trapped in porous rock -- or where the mixing of liquids is the essential point of the process. A key example of the latter is microfluidics technology, which allows for the controlled manipulation of fluids in miniscule channels often only a few hundred nanometers wide.

Microfluidic devices were first introduced in the 1980s and for many years were best known for their use in ink-jet printers, but have since been introduced in other fields, including the chemical analysis of blood or other sera in lab-on-a-chip technologies. These devices -- usually not much larger than a stick of chewing gum -- sometimes rely on nano-sized moving components, the geometry of the grooved channels or pulsed injections to induce a mixing of the fluids. But researchers in MIT's Department of Civil and Environmental Engineering suggest that a simpler method might be equally, if not more, effective.

"Getting two fluids to mix in a very tight space is difficult because there's not much room for a disorderly flow," said Professor Ruben Juanes, the ARCO Associate Professor in Energy Studies and principal investigator on the research. "But with two fluids of highly contrasting viscosity, the thinner fluid naturally creates disorder, which proves to be a marvelously efficient means of mixing."

In an analysis published online May 12 in Physical Review Letters (PRL), the researchers show that the injection of a thin or low-viscosity fluid into a much more viscous fluid (think of water spurting into molasses) will cause the two fluids to mix very quickly via a physical process known as viscous fingering. The thinner liquid, say the researchers, will form fingers as it enters the thicker liquid, and those fingers will form other fingers, and so on until the two liquids have mixed uniformly.

They also found that for maximum mixing to occur quickly, the ideal ratio of the viscosity of any two fluids depends on the speed at which the thinner liquid is injected into the thicker one.

The research team of Juanes, postdoctoral associate Luis Cueto-Felgueroso and graduate students Birendra Jha and Michael Szulczewski, made a series of controlled experiments using mixtures of water and glycerol, a colorless liquid generally about a thousand times more viscous than water. By alternating the viscosity of the liquids and the velocity of the injection flows, Jha was able to create a mathematical model of the process and use that to determine the best viscosity ratio for a particular velocity. He is lead author on the PRL paper.

"It's been known for a very long time that a low viscosity fluid will finger through the high viscosity fluid," said Juanes. "What was not known is how this affects the mixing rate of the two fluids. For instance, in the petroleum industry, people have developed increasingly refined models of how quickly the low viscosity fluid will reach the production well, but know little about how it will mix once it makes contact with the oil."

Similarly, Juanes said, in microfluidics technology, the use of fluids of different viscosities has not been seriously proposed as a mixing mechanism, but the new study indicates it could work very efficiently in the miniscule channels.

"We can now say that on average, the viscosity of the fluid injected should be about 10 times lower than that of the fluid into which it is injected," said Juanes. "If the contrast is greater than 10, then the injection should be done more slowly to achieve the fastest maximum mixing. Otherwise, the low viscosity fluid will create a single channel through the thicker fluid, which is not ideal."

Cueto-Felgueroso said a similar process is at work in the engraved channels of a microfluidic device and in subsurface rock containing oil. "Mixing fluids at small scales or velocities is difficult because you can't rely on turbulence: it would be hard to stir milk into your coffee if you were using a microscopic cup," Cueto-Felgueroso said. "With viscous fingering, you let the fluids do the job of stirring."

This work was funded by the Italian energy company, Eni, and the ARCO Chair in Energy Studies.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. The original article was written by Denise Brehm.

Journal Reference:

Birendra Jha, Luis Cueto-Felgueroso, Ruben Juanes. Fluid Mixing from Viscous Fingering. Physical Review Letters, 2011; 106 (19) DOI: 10.1103/PhysRevLett.106.194502

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Mixing fluids efficiently in confined spaces: Let the fingers do the working

ScienceDaily (May 13, 2011) — Getting two fluids to mix in small or confined spaces is a big problem in many industries where, for instance, the introduction of one fluid can help extract another -- like water pumped underground can release oil trapped in porous rock -- or where the mixing of liquids is the essential point of the process. A key example of the latter is microfluidics technology, which allows for the controlled manipulation of fluids in miniscule channels often only a few hundred nanometers wide.

Microfluidic devices were first introduced in the 1980s and for many years were best known for their use in ink-jet printers, but have since been introduced in other fields, including the chemical analysis of blood or other sera in lab-on-a-chip technologies. These devices -- usually not much larger than a stick of chewing gum -- sometimes rely on nano-sized moving components, the geometry of the grooved channels or pulsed injections to induce a mixing of the fluids. But researchers in MIT's Department of Civil and Environmental Engineering suggest that a simpler method might be equally, if not more, effective.

"Getting two fluids to mix in a very tight space is difficult because there's not much room for a disorderly flow," said Professor Ruben Juanes, the ARCO Associate Professor in Energy Studies and principal investigator on the research. "But with two fluids of highly contrasting viscosity, the thinner fluid naturally creates disorder, which proves to be a marvelously efficient means of mixing."

In an analysis published online May 12 in Physical Review Letters (PRL), the researchers show that the injection of a thin or low-viscosity fluid into a much more viscous fluid (think of water spurting into molasses) will cause the two fluids to mix very quickly via a physical process known as viscous fingering. The thinner liquid, say the researchers, will form fingers as it enters the thicker liquid, and those fingers will form other fingers, and so on until the two liquids have mixed uniformly.

They also found that for maximum mixing to occur quickly, the ideal ratio of the viscosity of any two fluids depends on the speed at which the thinner liquid is injected into the thicker one.

The research team of Juanes, postdoctoral associate Luis Cueto-Felgueroso and graduate students Birendra Jha and Michael Szulczewski, made a series of controlled experiments using mixtures of water and glycerol, a colorless liquid generally about a thousand times more viscous than water. By alternating the viscosity of the liquids and the velocity of the injection flows, Jha was able to create a mathematical model of the process and use that to determine the best viscosity ratio for a particular velocity. He is lead author on the PRL paper.

"It's been known for a very long time that a low viscosity fluid will finger through the high viscosity fluid," said Juanes. "What was not known is how this affects the mixing rate of the two fluids. For instance, in the petroleum industry, people have developed increasingly refined models of how quickly the low viscosity fluid will reach the production well, but know little about how it will mix once it makes contact with the oil."

Similarly, Juanes said, in microfluidics technology, the use of fluids of different viscosities has not been seriously proposed as a mixing mechanism, but the new study indicates it could work very efficiently in the miniscule channels.

"We can now say that on average, the viscosity of the fluid injected should be about 10 times lower than that of the fluid into which it is injected," said Juanes. "If the contrast is greater than 10, then the injection should be done more slowly to achieve the fastest maximum mixing. Otherwise, the low viscosity fluid will create a single channel through the thicker fluid, which is not ideal."

Cueto-Felgueroso said a similar process is at work in the engraved channels of a microfluidic device and in subsurface rock containing oil. "Mixing fluids at small scales or velocities is difficult because you can't rely on turbulence: it would be hard to stir milk into your coffee if you were using a microscopic cup," Cueto-Felgueroso said. "With viscous fingering, you let the fluids do the job of stirring."

This work was funded by the Italian energy company, Eni, and the ARCO Chair in Energy Studies.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. The original article was written by Denise Brehm.

Journal Reference:

Birendra Jha, Luis Cueto-Felgueroso, Ruben Juanes. Fluid Mixing from Viscous Fingering. Physical Review Letters, 2011; 106 (19) DOI: 10.1103/PhysRevLett.106.194502

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New properties of supercooled confined water discovered

ScienceDaily (May 12, 2011) — A study led by the UB researcher Giancarlo Franzese and published in the journal Physical Review Letters suggests that hydrophobic nanoconfinement can alter the thermodynamics of water at supercool temperatures. These findings may have important applications in fields related to conservation at cryogenic temperatures (around -100 ºC) -- for example, in the preservation of stem cells, blood and food products.

The team behind the study, led by Giancarlo Franzese from the UB's Department of Fundamental Physics, included researchers from Boston University and TU Berlin.

Water exhibits atypical fluid behaviour. One of its unique characteristics is the increase in heat capacity as water cools, an anomaly that enables us to regulate our body temperature. When water is supercooled -- that is, when it is in liquid state at a temperature below its melting point -- the range of anomalies expands. This irregular behaviour has generated fierce scientific debate over the last twenty years and could hold the key to understanding why water is so different to other liquids and why it is so important for biological organisms.

From a technical perspective, it is difficult to observe supercooled water directly and many researchers opt to use nanoconfinement. In this study, the team used Monte Carlo simulations to study a layer of water only one nanometre high -- approximately equivalent to the diameter of three water molecules -- confined between two hydrophobic plates. Hydrophobic nanoparticles were then added to the water layer in random positions to generate nanochannels or variable size.

This process led to a strong decrease in thermodynamic fluctuations, reflected in compressibility, thermal expansion coefficient and specific heat. The observed decrease occurred at all pressures tested, and at pressures in the region of 180 MPa fluctuations dropped by almost 99% for a concentration in nanoparticles of 25% by volume. The reduction was found to be as high as 90% even at a particle concentration ten times lower.

According to Giancarlo Franzese, the results show that the thermodynamic behaviour of water confined in hydrophobic nanochannels is very different to that of unconfined water, even allowing for the possible presence of more than one liquid phase within the range of temperatures and pressures tested.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Universidad de Barcelona, via AlphaGalileo.

Journal Reference:

Elena Strekalova, Marco Mazza, H. Stanley, Giancarlo Franzese. Large Decrease of Fluctuations for Supercooled Water in Hydrophobic Nanoconfinement. Physical Review Letters, 2011; 106 (14) DOI: 10.1103/PhysRevLett.106.145701

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here