Issue 43, 2015

Time scale of dynamic heterogeneity in model ionic liquids and its relation to static length scale and charge distribution

Abstract

We study how dynamic heterogeneity in ionic liquids is affected by the length scale of structural relaxation and the ionic charge distribution by the molecular dynamics simulations performed on two differently charged models of ionic liquid and their uncharged counterpart. In one model of ionic liquid, the charge distribution in the cation is asymmetric, and in the other it is symmetric, while their neutral counterpart has no charge with the ions. It is found that all the models display heterogeneous dynamics, exhibiting subdiffusive dynamics and a nonexponential decay of structural relaxation. We investigate the lifetime of dynamic heterogeneity, τdh, in these systems by calculating the three-time correlation functions to find that τdh has in general a power-law behavior with respect to the structural relaxation time, τα, i.e., Image ID:c5cp03390j-t2.gif. Although the dynamics of the asymmetric-charge model is seemingly more heterogeneous than that of the symmetric-charge model, the exponent is found to be similar, ζdh ≈ 1.2, for all the models studied in this work. The same scaling relation is found regardless of interactions, i.e., with or without Coulomb interaction, and it holds even when the length scale of structural relaxation is long enough to become the Fickian diffusion. This fact indicates that τdh is a distinctive time scale from τα, and the dynamic heterogeneity is mainly affected by the short-range interaction and the molecular structure.

Graphical abstract: Time scale of dynamic heterogeneity in model ionic liquids and its relation to static length scale and charge distribution

Supplementary files

Article information

Article type
Paper
Submitted
11 Jun 2015
Accepted
06 Oct 2015
First published
07 Oct 2015

Phys. Chem. Chem. Phys., 2015,17, 29281-29292

Author version available

Time scale of dynamic heterogeneity in model ionic liquids and its relation to static length scale and charge distribution

S. Park, S. Kim and Y. Jung, Phys. Chem. Chem. Phys., 2015, 17, 29281 DOI: 10.1039/C5CP03390J

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