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Issue 9, 2016
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Heterogeneous dynamics and its length scale in simple ionic liquid models: a computational study

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Abstract

We numerically investigate the dynamic heterogeneity and its length scale found in coarse-grained ionic liquid model systems. In our ionic liquid model systems, cations are modeled as dimers with a positive charge, while anions are modeled as monomers with a negative charge, respectively. To study the effect of the charge distributions on the cations, two ionic liquid models with different charge distributions are used and the model with a neutral charge is also considered as a counterpart. To reveal the heterogeneous dynamics in the model systems, we examine spatial distributions of displacement and time distributions of exchange and persistence times. All the models show a significant increase of the dynamic heterogeneity as the temperature is lowered. The dynamic heterogeneity is quantified via the well-known four-point susceptibility, χ4(t), which measures the fluctuations of a time correlation function. The dynamic correlation length is calculated by fitting the dynamic structure factor, S4(k,t), with the Ornstein–Zernike form at the time scale at which the dynamic heterogeneity reaches the maximum value. The obtained time and length scales exhibit a power law relation at the low temperatures, similar to various supercooled liquid models. In particular, the charged model systems show unusual crossover behaviors which are not observed in the uncharged model system. We ascribe the crossover behavior to the enhanced cage effect caused by charges on the particles.

Graphical abstract: Heterogeneous dynamics and its length scale in simple ionic liquid models: a computational study

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Supplementary files

Article information


Submitted
30 Nov 2015
Accepted
25 Jan 2016
First published
28 Jan 2016

Phys. Chem. Chem. Phys., 2016,18, 6486-6497
Article type
Paper
Author version available

Heterogeneous dynamics and its length scale in simple ionic liquid models: a computational study

S. Kim, S. Park and Y. Jung, Phys. Chem. Chem. Phys., 2016, 18, 6486
DOI: 10.1039/C5CP07368E

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