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Issue 20, 2018
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Anomalous diffusion of water molecules at grain boundaries in ice Ih

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Abstract

Using ab initio and classical molecular dynamics simulations, we study pre-melting phenomena in pristine coincident-site-lattice grain boundaries (GBs) in proton-disordered hexagonal ice Ih at temperatures just below the melting point Tm. Concerning pre-melt-layer thicknesses, the results are consistent with the available experimental estimates for low-disorder impurity-free GBs. With regard to molecular mobility, the simulations provide a key new insight: the translational motion of the water molecules is found to be subdiffusive for time scales from ∼10 ns up to at least 0.1 μs. Moreover, the fact that the anomalous diffusion occurs even at temperatures just below Tm where the bulk supercooled liquid still diffuses normally suggests that it is related to the confinement of the GB pre-melt layers by the surrounding crystalline environment. Furthermore, we show that this behavior can be characterized by continuous-time random walk models in which the waiting-time distributions decay according to power-laws that are very similar to those describing dynamics in glass-forming systems.

Graphical abstract: Anomalous diffusion of water molecules at grain boundaries in ice Ih

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Article information


Submitted
08 Feb 2018
Accepted
26 Apr 2018
First published
30 Apr 2018

Phys. Chem. Chem. Phys., 2018,20, 13944-13951
Article type
Paper

Anomalous diffusion of water molecules at grain boundaries in ice Ih

P. A. F. P. Moreira, R. G. D. A. Veiga, I. D. A. Ribeiro, R. Freitas, J. Helfferich and M. de Koning, Phys. Chem. Chem. Phys., 2018, 20, 13944
DOI: 10.1039/C8CP00933C

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