Supercooled Liquid Water Diffusivity at Temperatures near the Glass Transition Temperature

TL;DR

This study measures the diffusivity of supercooled liquid water near its glass transition temperature using isotopic layering and slow heating, providing evidence that amorphous water above Tg behaves like a normal supercooled liquid.

Contribution

It introduces a novel isotopic layering method combined with slow heating to accurately measure diffusivity near Tg of amorphous water.

Findings

Diffusivity indicates liquid-like motion near Tg.

Supports the thermodynamic continuity of amorphous water with supercooled liquid.

Diffusivity data aligns with the proposed Tg of 136 K.

Abstract

Isotopically layered amorphous solid water films were used to measure the diffusivity of deeply supercooled liquid water near the glass transition. The films, composed of separate layers of oxygen 16 and oxygen 18 labeled water, were grown by vapor deposition at low temperature and then heated to observe the intermixing of the isotopic layers. Very slow heating rates (as low as 0.0001 K/s) were used to decouple the diffusion and crystallization processes to ensure that the observed intermixing occurred at temperatures that were well-separated from the onset of crystallization. Numerical simulations of the desorption spectra were used to extract the translational diffusivities. The diffusivities obtained in this paper are consistent with translational liquid-like motion at temperatures near and above the proposed Tg of 136 K. These findings support the idea that the melt of amorphous water, above its glass transition temperature is thermodynamically continuous with normal supercooled liquid.