# Nanoscale domains in ionic liquids: A statistical mechanics definition for molecular dynamics studies

## TL;DR

This paper introduces a first-principles statistical mechanics definition of nanoscale domains in ionic liquids, using adaptive molecular resolution to identify atomistically self-contained nanodroplets, revealing heterogeneity scales.

## Contribution

It provides a rigorous, physics-based method to define and analyze nanoscale domains in ionic liquids, advancing beyond arbitrary criteria.

## Key findings

- Identification of atomistic nanodroplets in ILs
- Quantitative measure of heterogeneity length scale
- Application to four different imidazolium-based ILs

## Abstract

One of the many open questions concerning Ionic Liquids (ILs) is the existence of nanoscale supramolecular domains which characterize the bulk. The hypothesis of their existence does not meet a general consensus since their definition seems to be based on ad hoc arbitrary criteria rather than on general and solid first principles of physics. In this work, we propose a suitable definition of supramolecular domains based on first principles of statistical mechanics. Such principles can be realized through the application of a recently developed computational tool which employs adaptive molecular resolution. The method can identify the smallest region of a liquid for which the atomistic details are strictly required, while the exterior plays the role of a generic structureless thermodynamic reservoir. We consider four different imidazolium-based ILs and show that indeed one can quantitatively represent the liquid as a collection of atomistically self-contained nanodroplets embedded in a generic thermodynamic bath. Such nanodroplets express a characteristic length scale for heterogeneity in ILs.