Too much heat can destroy a sturdy automobile engine or a miniature microchip. As scientists and engineers strive to make ever-smaller nanoscale devices, from molecular motors and switches to single-molecule transistors, the control of heat is becoming a burning issue.
The shapes of molecules really matter, say scientists from the University of Illinois at Urbana-Champaign and the University of Scranton who timed the flow of vibrational heat energy through a water-surfactant-organic solvent system. The rate at which heat energy moves through a molecule depends specifically on the molecule’s structure, they found. "The flow of vibrational energy across a molecule is dependent upon where and how the energy is deposited," said Dana Dlott, a professor of chemistry at Illinois and a co-author of a paper to appear in the journal Science, as part of the Science Express Web site, on Sept. 23. "Unlike normal heat conduction, different excitations may travel across the molecule along different paths and at different rates."
To monitor energy flow, Dlott and his colleagues - Scranton chemistry professor John Deak, Illinois postdoctoral research associate Zhaohui Wang and graduate student Yoonsoo Pang, and Scranton undergraduate student Timothy Sechler - used an ultrafast laser spectrometer technique with picosecond time resolution.
The system the scientists studied is called a reverse micelle, and consisted of a nanodroplet containing 35 water molecules enclosed in a sphere of surfactant (sodium dioctyl sulfosuccinate) one molecule thick that was suspended in carbon tetrachloride. The ultrafast laser technique, developed at Illinois, monitored vibrational energy flow as it moved from water, through the surfactant shell out to the organic solvent, atom by atom.
When the researchers deposited energy in the nanodroplet, the vibrations moved through the surfactant and into the carbon tetrachloride within 10 picoseconds. However, when the energy was deposited directly into the surfactant, the vibrations required 20 to 40 picoseconds to move into the carbon tetrachloride. Even though the distance was shorter, the energy transfer took significantly longer. "This is opposite of what you would think in terms of simple and ordinary heat conduction," Dlott said. "To explain this strange result, we have to analyze the energy transfer in terms of specific vibrational couplings that occur through a vibrational cascade."
There are hundreds of different vibrations in the water-surfactant-organic solvent system, Dlott said. "When energy moves through molecules, the detailed structure of the molecules and the way the vibrations interact are extremely important."
When the water was excited by a laser pulse, the scientists report, much of the energy was immediately moved to the surfactant, which then efficiently transferred the energy to the carbon tetrachloride. But when the surfactant was excited by the laser, the energy took a different path among the atoms, delaying the transfer to the carbon tetrachloride.
"The movement of vibrational energy within and between molecules is a fundamental process that plays a significant role in condensed matter physics and chemistry," Dlott said. "In designing nanoscale devices, the shapes of the molecules must be designed not only to be small and fast, but also to efficiently move heat."
The National Science Foundation, the Air Force Office of Scientific Research and the U.S. Department of Energy supported this work.
James E. Kloeppel | University of Illinois
Further Improvement of Qubit Lifetime for Quantum Computers
09.12.2016 | Forschungszentrum Jülich
Electron highway inside crystal
09.12.2016 | Julius-Maximilians-Universität Würzburg
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine