Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water

TLDR

The study aims to identify the end point of the fragile‑to‑strong transition as a candidate for a second critical point in supercooled water. Water is confined in silica nanopores and probed by neutron scattering to suppress crystallization and examine pressure effects on its dynamics. Neutron scattering reveals a cusplike fragile‑to‑strong transition whose temperature drops with pressure, intersecting the homogeneous nucleation line at ~1600 bar, beyond which the transition signature vanishes.

Abstract

By confining water in nanopores of silica glass, we can bypass the crystallization and study the pressure effect on the dynamical behavior in deeply supercooled state using neutron scattering. We observe a clear evidence of a cusplike fragile-to-strong (FS) dynamic transition. Here we show that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS transition. Identification of this end point with the possible second critical point is discussed.