Squeezout phenomena and boundary layer formation of a model ionic liquid under confinement and charging

TL;DR

This study uses molecular dynamics simulations to investigate how nanoscale confinement and electrical charging induce structural, phase, and squeezout phenomena in a model ionic liquid, revealing charge-dependent layering and phase transitions.

Contribution

It introduces a detailed simulation analysis of ionic liquid behavior under confinement and charging, highlighting charge-induced layering, solidification, melting, and squeezout effects in a simplified model.

Findings

Charge induces layering and structural switching.

Squeezout behavior depends on plate charge and ionic arrangement.

Effective enthalpy reveals stable layered states and transitions.

Abstract

Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. That includes even-odd switching of the structural layering and charging-induced solidification and melting, with important changes of local ordering between and within layers, and of squeezout behavior. By means of molecular dynamics simulations, we explore this variety of phenomena in the simplest charged Lennard-Jones coarse-grained model including or excluding the effect a neutral tail giving an anisotropic shape to one of the model ions. Using these models and open conditions permitting the flow of ions in and out of the interplate gap, we simulate the liquid squeezout to obtain the distance dependent structure and forces between the plates during their adiabatic appraoch under load. Simulations at fixed applied force illustrate an effective electrical pumping of the ionic liquid, from a thick nearly solid film that withstands the interplate pressure for high plate charge to complete squeezout following melting near zero charge. Effective enthalpy curves obtained by integration of interplate forces versus distance show the local minima that correspond to layering, and predict the switching between one minimum and another under squeezing and charging.