Nanocapillary Confinement of Imidazolium Based Ionic Liquids

TL;DR

This study investigates how nanocapillary confinement affects the structural and conductive properties of imidazolium-based ionic liquids, revealing they maintain glass-like behavior even at very small confinement scales.

Contribution

First conductivity measurements of ionic liquids in single conical glass nanopores, showing no long-range freezing effects down to 20 nm confinement.

Findings

Ionic liquids exhibit glass-like behavior across all tested confinements.

No long-range structural ordering or freezing observed at nanoscale confinement.

Conductivity remains consistent despite confinement down to 20 nm.

Abstract

Room temperature ionic liquids are salts which are molten at or around room temperature without any added solvent or solution. In bulk they exhibit glass like dependence of conductivity with temperature as well as coupling of structural and transport properties. Interfaces of ionic liquids have been found to induce structural changes with evidence of long range structural ordering on solid-liquid interfaces spanning length scales of $10-100$nm. Our aim is to characterize the influence of confinement on the structural properties of ionic liquids. We present first conductivity measurements on ionic liquids of the imidazolium type in single conical glass nanopores with confinements as low as tens of nanometers. We probe glassy dynamics of ionic liquids in a large range of temperatures ($-20$ to $70^\circ$C) and nanopore opening sizes ($20-600$nm) in silica glass nanocapillaries. Our results indicate no long range freezing effects due to confinement in nanopores with diameters as low as $20$nm. The studied ionic liquids are found to behave as glass like liquids across the whole accessible confinement size and temperature range.