Could Carbon Nanotube “Ice Wires” Be the Conductor of the Future?January 25, 2017 by Mark Hughes
Scientists at MIT have verified the solid state of H₂O inside carbon nanotubes at temperatures above 105°C.
Researchers at MIT have found that in certain diameter carbon nanotubes, a solid phase of H2O can exist at temperatures greater than 105 °C (378 K).
It's long been known that, given different amounts of space, the boiling and freezing points of water can change. MIT researchers have taken this fact and tested it at the microscopic level.
What they found is the increased pressure of a carbon nanotube only a few water molecules wide can keep water frozen beyond boiling temperatures. This changes the long-held view of what people know as the traditional characteristics of phases of matter for water.
Phases of Matter
While many phases of matter exist, most of the materials that we are encounter in everyday life exist in one of the three common states: solid, liquid, and gas. Water covers most of this planet, and a lifetime of experience has taught us that ice is cold, steam is hot, and liquid water is somewhere in between. But that is only because in our day to day interactions with water occur at approximately the same pressure (~ 0.1 MPa.) Researchers in the Strano Research Group at MIT have found that in certain carbon nanotubes, a solid phase of H2O can exist at temperatures greater than 105 °C (378 K.)
Simplistic Pressure vs. Temperature Phase Plot data from Wolfram Alpha and edited with Mathematica
Water has many more phases than the three that are typically encountered, and each phase corresponds to a particular set of uniform properties.
Advanced pressure vs. temperature phase plot from lsbu.ac.uk that shows many more phases of water. By Martin Chaplin [CC BY-SA 3.0]
When photons of light strike an atom or molecule the energy may be absorbed and reemitted. You may be familiar with fluorescence, where high energy photons are absorbed and then spontaneously re-emitted at the same or lower energy level. The frequency of the light is directly proportional to the difference in two energy levels of electrons. All atoms have unique allowed energy states and a unique spectrum that corresponds to the difference of energy levels.
Left: A depiction of photon absorption and emission from StackExchange. Top-right: UV light causes Uranium-infused glass to fluoresce (photo by Mark Hughes). Bottom-right: Visible emission spectrum of Uranium-II from Wolfram Alpha.
Light from the atoms or molecules is then passed through or reflected off of a grating, and constructive interference at certain locations causes bright lines to form.
Image of diffraction from Slideplayer.com
In 1928, C. V. Raman discovered that some of the light scattered at 90° from a molecule would have a slightly different frequency than the incident light. A very small fraction of the light would have a slightly higher frequency, and a very small fraction of the light would have a lower frequency. These frequencies correspond to energy transitions in the scattering molecule and allow the determination of vibrational and rotational states for a molecule.
Diagrammatic description of Raman Spectroscopy from the University of Pennsylvania.
In Raman Spectroscopy, monochromatic light (typically from a laser) is shown on a molecule. The light that is scattered off of the sample is primarily of the incident frequency and is optically filtered out. The remaining frequencies of light are very dim lines that are reflected off of a diffraction grating and into a camera for analysis.
Carbon Nanotubes and Ice Water
Carbon atoms join together to create cylinders of very small diameter. The electron band structure is dependent on the pattern of arrangement of the atoms. Some nanotubes function as semiconductors, and others as metals. See this article to learn more about nanotube properties.
Artistic Interpretation of Water Inside a [9,9] armchair nanotube by Mark Hughes
Researchers discovered that nanotube geometries influenced the phase transition temperatures of H2O. And it is possible for a solid phase of water to be present in a 1.05 nm single wall carbon nanotube at temperatures up to 138 °C.
|Abbreviated Data Table|
|Diameter [nm]||Solid-Liquid Transition [°C]||Liquid-Vapor Transition [°C]|
Abbreviated data table from the Supplementary Information (PDF). Provided by the authors.
Certain carbon nanotubes already exhibit the property of ballistic conduction (negligible resistivity due to scattering). This means electrons can travel freely along the length of the nanotube until it collides at the end of the tube. The solid H2O at high temperatures means that protons may be transported as well. While copper is the dominant conductor of choice in the market today, and will likely stay that way for a long time, future generations might see devices and power transmission lines made of carbon nanotubes filled with solid H20.
Featured image used courtesy of MIT.