Speaker
Dr
Jonas Sellberg
(Stockholm University)
Description
Experiments on pure bulk water below about 235 K have so far
been difficult: crystallization occurs very rapidly below
the homogeneous nucleation temperature of 232 K and above
~160 K in bulk water, leading to a “no man’s land” devoid of
experimental results. In my talk, I will present successful
measurements to study the structure of bulk water below 232
K and derive the homogeneous ice nucleation rate. Using
femtosecond x-ray pulses generated by the world's first hard
x-ray laser to probe evaporatively cooled droplets of
supercooled water, we find experimental evidence for the
existence of metastable bulk liquid water down to
temperatures of 227 K in the previously largely unexplored
“no man’s land”. The occurrence of crystallization within
the water droplets increased rapidly below 232 K, from which
the nucleation rate was derived. We observed a slower rate
than anticipated from previous experiments, which can be
explained by a rapid decrease in water's diffusivity. These
findings are consistent with the proposed
"fragile-to-strong" transition expected to occur upon deep
supercooling. Finally, I will conclude with an outlook of
future experiments on water and ice using x-ray lasers.
