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Related Experiment Video

Updated: Jun 17, 2026

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Published on: March 24, 2018

Three-dimensional electric double layer at the solvent-free liquid/liquid interface between two immiscible ionic

Kazuma Yamaguchi¹, Kazuya Kobayashi¹, Kosuke Ishii²

¹Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan. nishi.naoya.7e@kyoto-u.ac.jp.

Physical Chemistry Chemical Physics : PCCP

|June 16, 2026

Summary

Molecular dynamics simulations reveal a unique three-dimensional electric double layer (EDL) at liquid/liquid interfaces. Smaller ions from hydrophilic ionic liquids (ILs) form overscreening layers within interfacial pockets, unlike conventional oil/water interfaces.

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Published on: December 20, 2016

Area of Science:

Physical Chemistry
Materials Science
Computational Chemistry

Background:

The electric double layer (EDL) structure at liquid/liquid interfaces is crucial for electrochemical applications.
Conventional oil/water interfaces exhibit a two-dimensional EDL, limited by ion hydration and interfacial roughness.

Purpose of the Study:

To investigate the EDL structure at a solvent-free ionic liquid/ionic liquid (IL/IL) interface.
To compare the EDL structure at IL/IL interfaces with conventional oil/water interfaces.

Main Methods:

Molecular dynamics (MD) simulations were employed to model the interface between hydrophobic trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide (TOMAC4C4N) and hydrophilic ethylammonium nitrate (EAN).
Analyses included charge density distribution and radial distribution functions to characterize ion behavior and interfacial structure.

Main Results:

A three-dimensional EDL was observed at the IL/IL interface, characterized by smaller hydrophilic ions inserting into interfacial pockets formed by capillary waves of larger hydrophobic ions.
Overscreening ionic layers formed due to the absence of solvent, enabling close interactions between counterions and larger ions.
This unique EDL structure, driven by ion amphiphilicity and interfacial ion organization, was also observed at other liquid/liquid interfaces.

Conclusions:

The EDL structure at IL/IL interfaces differs significantly from conventional interfaces, forming a three-dimensional structure due to specific ion interactions and the absence of solvent.
The amphiphilicity of ions and the organization of larger ions at the interface are key factors determining the EDL structure.
The phenomenon of "ionic liquid fingers" was observed when smaller ions transferred between phases, highlighting complex interfacial dynamics.