Second critical point of water in supercooled confined water in L,L-diphenylalanine micro/nanotubes

TL;DR

This study investigates the low-temperature behavior of supercooled confined water in nanotubes, revealing a second critical point and a fragile-to-strong transition at 204 K, supported by Raman spectroscopy and mode-coupling theory.

Contribution

It provides experimental evidence for a second critical point of water in confined environments using Raman spectroscopy and mode-coupling analysis.

Findings

Identification of a fragile-to-strong transition at 204 K.

Evidence supporting the existence of a second critical point of water.

Agreement between experimental data and mode-coupling theory.

Abstract

The temperature dependence (10-290 K) of the low-frequency (20-150 cm-1) Raman-active phonon modes of supercooled confined water in L,L-diphenylalanine micro/nanotubes was analysed. The isolated dynamics of a specific geometry of water cluster (pentamer) in supercooled confined regime was studied in detail. A particular mode concerning water-nanotube interaction was also probed. A fragile-to-strong transition at 204 K was observed and related to the crossing of the Widom line. The critical exponent analyses of the relaxation rate data based on mode-coupling theory indicated perfect agreement among experimental data and theory. Our results are consistent with the existence of a second critical point of water.