Journal of Physical Chemistry C
Journal of Physical Chemistry C
5 years ago

Transient Translational and Rotational Water Defects in Gas Hydrates

Transient Translational and Rotational Water Defects in Gas Hydrates
Deqing Liang, Lizhi Yi, Nengyou Wu, Shuai Liang, Gaowei Hu
We report our observations of the transient formation of the translational and rotational defects in the host lattice of methane hydrates. We perform molecular dynamics simulations of a fully occupied methane hydrate system and find that the hydrogen bonds of a water molecule can be thermally broken, and the water molecule can then rotate more freely. We observe the formation of transient Bjerrum defects around the water molecule, and the two hydrogens of the water molecule can be interchanged when the transient defects anneal. The 95% confidence interval for the rate of the hydrogen interchange is estimated to be 1.3 × 105–2.4 × 105 s–1 per water molecule, and the 95% confidence interval for the associated free energy of activation is estimated to be 38.2–39.4 kJ/mol at 270 K. We also observe the transient formation of vacancy-interstitial water defects. The formation and annealing of these vacancy-interstitial defects can result in the interchange of two or three neighboring water molecules on the gas hydrate lattices. The 95% confidence interval for the rate of the formation of transient vacancy-interstitial water defects as a result of the water interchanges is estimated to be 6.7 × 102–1.6 × 104 s–1 per water molecule, and the 95% confidence interval for the associated free energy of activation is estimated to be 44.1–51.3 kJ/mol at 270 K.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04310

DOI: 10.1021/acs.jpcc.7b04310

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