Communication: Influence of nanophase segregation on ion transport in room temperature ionic liquids

Philip J. Griffin; Yangyang Wang; Adam P. Holt; Alexei P. Sokolov

doi:10.1063/1.4947552

Communication: Influence of nanophase segregation on ion transport in room temperature ionic liquids

Philip J. Griffin, Yangyang Wang, Adam P. Holt, Alexei P. Sokolov

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16 Scopus citations

Abstract

We report measurements of the ionic conductivity, shear viscosity, and structural dynamics in a homologous series of quaternary ammonium ionic liquids (ILs) and a prototypical imidazolium-based IL over a wide range of temperatures down to the glass transition. We find that the ionic conductivity of these materials generally decreases, while the shear viscosity correspondingly increases, with increasing volume fraction of aliphatic side groups. Upon crossing an aliphatic volume fraction of ∼0.40, we observe a sharp, order-of-magnitude decrease in ionic conductivity and enhancement of viscosity, which coincides with the presence of long-lived, nanometer-sized alkyl aggregates. These strong changes in dynamics are not mirrored in the ionicity of these ILs, which decreases nearly linearly with aliphatic volume fraction. Our results demonstrate that nanophase segregation in neat ILs strongly reduces ionic conductivity primarily due to an aggregation-induced suppression of dynamics.

Original language	English
Article number	151104
Journal	Journal of Chemical Physics
Volume	144
Issue number	15
DOIs	https://doi.org/10.1063/1.4947552
State	Published - Apr 21 2016

Funding

The authors thank NSF chemistry for financial support of this work through Grant No. CHE-1213444. We thank J. Sangoro and V. Novikov for helpful discussions.

Funders	Funder number
National Science Foundation	CHE-1213444
Directorate for Mathematical and Physical Sciences	1213444

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title = "Communication: Influence of nanophase segregation on ion transport in room temperature ionic liquids",

abstract = "We report measurements of the ionic conductivity, shear viscosity, and structural dynamics in a homologous series of quaternary ammonium ionic liquids (ILs) and a prototypical imidazolium-based IL over a wide range of temperatures down to the glass transition. We find that the ionic conductivity of these materials generally decreases, while the shear viscosity correspondingly increases, with increasing volume fraction of aliphatic side groups. Upon crossing an aliphatic volume fraction of ∼0.40, we observe a sharp, order-of-magnitude decrease in ionic conductivity and enhancement of viscosity, which coincides with the presence of long-lived, nanometer-sized alkyl aggregates. These strong changes in dynamics are not mirrored in the ionicity of these ILs, which decreases nearly linearly with aliphatic volume fraction. Our results demonstrate that nanophase segregation in neat ILs strongly reduces ionic conductivity primarily due to an aggregation-induced suppression of dynamics.",

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AB - We report measurements of the ionic conductivity, shear viscosity, and structural dynamics in a homologous series of quaternary ammonium ionic liquids (ILs) and a prototypical imidazolium-based IL over a wide range of temperatures down to the glass transition. We find that the ionic conductivity of these materials generally decreases, while the shear viscosity correspondingly increases, with increasing volume fraction of aliphatic side groups. Upon crossing an aliphatic volume fraction of ∼0.40, we observe a sharp, order-of-magnitude decrease in ionic conductivity and enhancement of viscosity, which coincides with the presence of long-lived, nanometer-sized alkyl aggregates. These strong changes in dynamics are not mirrored in the ionicity of these ILs, which decreases nearly linearly with aliphatic volume fraction. Our results demonstrate that nanophase segregation in neat ILs strongly reduces ionic conductivity primarily due to an aggregation-induced suppression of dynamics.

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Communication: Influence of nanophase segregation on ion transport in room temperature ionic liquids

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