Liquid water at 170 degrees Celsius
X-ray laser reveals anomalous dynamics at ultra-fast heating

Date:
September 16, 2020
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
Using an X-ray laser, a research team has investigated how water
heats up under extreme conditions. In the process, the scientists
were able to observe water that remained liquid even at temperatures
of more than 170 degrees Celsius. The investigation revealed
an anomalous dynamic behavior of water, which is of fundamental
importance for investigations of sensitive samples using X-ray
lasers.



FULL STORY ========================================================================== Using the X-ray laser European XFEL, a research team has investigated how
water heats up under extreme conditions. In the process, the scientists
were able to observe water that remained liquid even at temperatures of
more than 170 degrees Celsius. The investigation revealed an anomalous
dynamic behaviour of water under these conditions. The results of the
study, which are published in the Proceedings of the National Academy
of Sciences (PNAS), are of fundamental importance for the planning and
analysis of investigations of sensitive samples using X-ray lasers.


========================================================================== European XFEL, an international research facility, which extends from
the DESY site in Hamburg to the neighbouring town of Schenefeld in Schleswig-Holstein, is home to the most powerful X-ray laser in the
world. It can generate up to 27,000 intense X-ray flashes per second. For
their experiments, the researchers used series of 120 flashes each. The individual flashes were less than a millionth of a second apart (exactly
0.886 microseconds). The scientists sent these pulse trains into a thin, water-filled quartz glass tube and observed the reaction of the water.

"We asked ourselves how long and how strongly water can be heated in
the X-ray laser and whether it still behaves like water," explains
lead author Felix Lehmku"hler from DESY. "For example, does it still
function as a coolant at high temperatures?" A detailed understanding of superheated water is also essential for a large number of investigations
on heat-sensitive samples, such as polymers or biological samples.

"With the X-ray flashes, we were able to heat the water up to 172 degrees Celsius within a ten thousandth of a second without it evaporating,"
reports Lehmku"hler. Such a boiling delay can normally only be observed
up to about 110 degrees Celsius. "But that is not the only anomalous
feature," the physicist emphasises. The scientists investigated the
movement of silicon nanospheres floating in the water as markers for the dynamics in the sample. "In the extremely overheated water, we observed
that the movement of silicon dioxide nanospheres deviated significantly
from the expected random Brownian molecular movement. This indicates an
uneven heating of the sample," says Lehmku"hler.

Existing theoretical models cannot yet satisfactorily explain this
behaviour because they are not designed for water under these extreme conditions.

Thanks to the rapid flash sequence of the European XFEL, the researchers
were able to observe the process in extreme detail. "What makes the
European XFEL unique is the high repetition rate, that is, the high
number of pulses per second," explains co-author Adrian Mancuso, head of
the SPB/SFX instrument at the European XFEL where the experiments took
place. "And we have all the instrumentation in place -- such as fast
cameras, diagnostics and more -- to make these experiments possible." For instance, the Adaptive Gain Integrating Pixel Detector (AGIPD) developed
by a DESY-led consortium can take around 350 serial images at intervals
of only 220 billionths of a second (nanoseconds).

This setup not only allowed the superheated water to be generated, but
also enabled the scientists to carry out precisely controlled series
of experiments with X-ray flashes of reduced intensity. "Using silicon
filters, we fine-tuned the energy of the pulses so that we were able to
control exactly how much the water was heated," reports Lehmku"hler. "For example, we were able to determine how strong the X-ray flashes should
be so that the temperature of an aqueous sample remains more or less
constant." This enables researchers to better plan experiments with heat-sensitive samples at the X-ray laser, for example. On the other hand,
the heating effect can also be used in a targeted manner if its exact
course is known. The team plans to further investigate these effects
also within the framework of the Centre for Molecular Water Science
(CMWS), which is currently being set up at DESY.

"Our results not only provide the surprising observation of an anomalous dynamic, but also draw a detailed picture of how aqueous samples heat
up in the X-ray laser," summarises lead researcher Gerhard Gru"bel from
DESY, one of the CMWS coordinators. "In addition, the investigations
prove that such serial images are possible at the European XFEL and that
its flashes are extremely uniform in every pulse train."

========================================================================== Story Source: Materials provided by
Deutsches_Elektronen-Synchrotron_DESY. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Felix Lehmku"hler, Francesco Dallari, Avni Jain, Marcin Sikorski,
Johannes Mo"ller, Lara Frenzel, Irina Lokteva, Grant Mills,
Michael Walther, Harald Sinn, Florian Schulz, Michael Dartsch,
Verena Markmann, Richard Bean, Yoonhee Kim, Patrik Vagovic, Anders
Madsen, Adrian P.

Mancuso, Gerhard Gru"bel. Emergence of anomalous dynamics in soft
matter probed at the European XFEL. Proceedings of the National
Academy of Sciences, 2020; 202003337 DOI: 10.1073/pnas.2003337117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113504.htm

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