Supercooled Water Researcher Finds SEQUOIA’s Power “Amazing”
SNS services include rescuing user in a snowstorm
Research Contacts: Roberto Senesi, Garrett Granroth
June 2011, Written by Deborah Counce
Scattering from water at 3 eV incident energy. The scattering is centered at the proton recoil energies.
East Tennessee generally enjoys a temperate climate, even in winter. But when a research team from the Università degli Studi di Roma “Tor Vergata,” Italy, visited the SNS on the Oak Ridge National Laboratory campus last December, the area was hit by one of its rare winter snowstorms. Roberto Senesi, the principal investigator on the experiment the team was doing at the SEQUOIA chopper spectrometer, narrowly escaped having to spend the night at the instrument and miss his plane home the next morning—he was rescued by ORNL Neutron Sciences Director Ian Anderson.
The international collaboration included Carla Andreani and Davide Flammini, all from Rome, Roberto Car from Princeton University, and Alexander Kolesnikov from the Neutron Scattering Sciences Division at ORNL. They took advantage of SEQUOIA’s unique high neutron flux and fine energy resolution to study the vibrational spectrum of supercooled water (below 273 K) close to the triple point.
“There is a strong relationship between supercooled water and confined water, such as water around the surface of proteins,” Senesi said. “Understanding the mechanisms by which protons vibrate in water around the temperature of freezing can help to understand how water assists the functional properties of proteins and macromolecules, such as DNA.”
Even before they arrived, the Italians worked with the SNS Sample Environment team to design and make the unique containers for the experiment. The aluminum containers were designed and manufactured at SNS and then shipped to Rome, where they were PFTE-coated by Praxair-Smaltiriva, a company in Mantova, northern Italy. The newly-coated containers were then shipped back to SNS. “People at SNS liked the coating. They have since asked for another 50 cell coatings from the same company for other projects,” Senesi recalls.
Senesi arrived two days before the experiment. “The User Office and the Experiment Hall team are of top quality,” he said, “and very efficient. I was particularly impressed by the Instrument Hall coordinators, who are there 24 hours a day, 7 days a week, to assist users with their experiments—this is an amazing resource and one that I greatly appreciated.
“I was impressed by the lively atmosphere at the facility. People seemed to enjoy their work, having the possibility to put in practice their passion about what is done at the SNS. I was also able to meet friends and colleagues—it’s becoming a hub,” said Senesi.
To begin, Senesi and his team got thorough training in radiation safety. Then they were taken in charge by Garrett Granroth, lead instrument scientist on SEQUOIA, and instrument scientist Alexander Kolesnikov. “In our previous study using the Vesuvio spectrometer at ISIS in the UK, we found that the kinetic energy of protons in water is greatly enhanced when liquid water is cooled below 273 K (supercooled liquid water),” Senesi said. “During a conference in 2009 in Knoxville, Dr. Kolesnikov discussed this result with me and proposed that the mechanism for this unusual behavior may be ascribed to the behavior of the OH stretching motion in water in the different phases. We agreed to prepare an experiment proposal for SEQUOIA,” Senesi recalled.
During the final preparation of the sample environment, “the technical staff was very proactive, making all the final leak, temperature, and other tests. The container was designed to hold a sample of water in the temperature range 260 K to 280 K, accessing the liquid, the solid, and the liquid supercooled phases below 273 K.” It was designed to have the maximum scattering intensity from the sample, the minimum scattering intensity from the container, the minimum multiple scattering, the most favorable geometry (flat), and a perfectly flat hydrophobic internal surface. The latter requirement is crucial to allow water to remain liquid below freezing temperature (supercooling below 273 K).
“The power of the neutron source is amazing,” Senesi said. “I am used to 12 to 24 hours of acquisition for one sample temperature, but here the acceleration factor makes a big difference, and not just quantitative.” SEQUOIA was able to access the entire spectroscopic range required for the investigation of the OH vibrations in a single experiment, and the very high intensity made it possible to measure at many different temperatures, across the various phases. “We also wanted to access the high incident neutron energies, greater than 3 eV, where it is possible to measure the proton kinetic energies directly. SEQUOIA had the intensity and flexibility to fulfill all these requirements.”
The science went smoothly over the three-day experiment. On the third day came the snow. “Sunday, December 12, was my last day, so I came to the lab to look after the experiment,” Senesi recalled. During that day, snow started to fall in Oak Ridge, and it became very intense in the afternoon. I had a dinner appointment in Oak Ridge that evening, so at 6.30, I left SEQUOIA and went to the main SNS entrance to wait for my taxi.
“The taxi never arrived, and I phoned them several times, without response. At 7 p.m. I went back to the Experiment Hall team, and they contacted four or five companies, but because of the snow, no taxi was driving in the area, including my early morning taxi that was booked to get me to Knoxville airport.
“I was a bit lost, since there was no easy way to get back to my hotel and I was worried about getting to the airport the next morning. Fortunately for me, Ian Anderson was in the building, checking on activities, and he offered to brave the storm to take me back to the hotel. After dinner I managed, after several internet searches and phone calls, to book a taxi for 3 a.m. to get me to the airport.
“I feel very grateful to Ian! I must admit that I was prepared to spend the night in the lab, since it is not easy to reach the ORNL main entrance on foot, or by hitchhiking!”
Senesi said the research done at SEQUOIA complements the team’s first set of measurements taken at ISIS. The researchers are now analyzing their data. NSSD’s Kolesnikov showed Senesi the user interface and the main data reduction routines that are applied to treat the raw data. “It is possible to access all routines remotely from a Web interface, and save all intermediate steps of the data processing, to be recovered at any later stage.”
The international collaboration is returning to SEQUOIA for another water experiment, but this time at high temperature/pressures, in the supercritical phase. This is a state of water that is relevant for the development of novel nuclear reactors. C. Loong of Tsinghua University in China is the principal investigator.
This work is funded by University of Roma Tor Vergata and the other partner institutions. The experiment at SNS was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. ORNL is managed by UT–Battelle, LLC, under contract DE-AC0500OR22725 for the U.S. Department of Energy.
