November 24, 2020
Using x-ray lasers, researchers at Stockholm University have
been able to follow the transformation between two distinct
different liquid states of water, both being made of H2O
At around -63º Centigrade
the two liquids exist at different pressure regimes with a density
difference of 20%. By rapidly varying the pressure before the sample
could freeze, it was possible to observe one liquid changing into
the other in real time.
Their findings (Experimental
observation of the Liquid-Liquid transition in bulk Supercooled
Water under Pressure) are published in the Journal
Water, both common
and necessary for life on Earth, behaves very strangely in
comparison with other substances.
properties such as density, specific heat, viscosity and
compressibility respond to changes in pressure and temperature
is completely opposite to other liquids that we know.
is often called "anomalous". If water would have behaved as a
"normal liquid" we would not exist, since marine life could not
However, it is still
an open question:
what causes these
There have existed a
number of explanations to the strange properties of water and one of
them propose that water has the ability to exist as two different
liquids at different pressures and at low temperatures.
If we would be able to
keep the two liquids in a glass they would separate with a clear
interface in between, as for water and oil (below figure).
Ordinary water at our
ambient conditions is only one liquid and no interface would be seen
in a glass - but on a molecular level, it fluctuates creating small
local regions of similar density as the two liquids, causing water's
The challenge has been
that no experiment has been possible at the temperatures where the
two liquids would co-exist since ice would form almost
Up to now it has only
been possible to investigate water at these conditions using
different types of computer simulations, which has led to a lot of
contradicting results depending on the model used.
"What was special was
that we were able to X-ray unimaginably fast, before the water
froze, and could observe how one liquid transformed to the
other", says Anders Nilsson, Professor of Chemical
Physics at Stockholm University.
"For decades, there
has been speculations and different theories to explain these
anomalous properties and why they get stronger when water
Now we have found
that the two liquid states are real and can explain the water
"I have studied several forms of disordered ices for a long time
with the goal to determine whether they can be considered a
glassy state representing a frozen liquid", says Katrin
Amann-Winkel, Senior Researcher in Chemical Physics at
"It is a dream come
true to see that indeed they represent real liquids and we see
the transformation between them".
"We worked so hard for several years to conduct measurements of
water under such low temperature conditions without freezing and
it is so rewarding to see the outcome", says Harshad Pathak,
Researcher in Chemical Physics at Stockholm University.
"Many attempts over
the world have been made to look for the two liquids by putting
water in tiny compartments or mixing it with other compounds but
here we could follow it as simple pure water".
"I wonder if the two liquid states as fluctuations could be an
important ingredient to the biological processes in living
cells", says Fivos Perakis, Assistant Professor in
Chemical Physics at Stockholm University.
"The new result can
open up many new research directions also about water in
"Maybe one of the liquid forms is more prominent for water in
small pores inside membranes used to desalinate water", says
Marjorie Ladd Parada, Postdoc at Stockholm University.
"I think the access
to clean water will be one of the major challenges with climate
"There has been an intense debate about the origin of the
strange properties of water for over a century since the early
work of Wolfgang Röntgen", further explains Anders Nilsson.
the physics of water can now settle on the model that water can
exist as two liquids in the supercooled regime.
The next stage is to
find if there is a critical point when the two liquids cross
over to become only one liquid, as the pressure and temperature
A big challenge for
the next few years."
The study was done in
cooperation with the,
University in Korea
PAL-XFEL in Korea
accelerator laboratory in California
of the City University of New York in USA
Xavier University in Canada
Other people that
contributed to the study include previous members of the Chemical
Physics group at Stockholm University,
Kyung Hwan Kim,
Alexander Späh, Daniel Mariedahl, Tobias Eklund and Matthew