Structural forces in mixtures of ionic liquids with organic solvents
File(s)
Author(s)
Pivnic, K
Bresme, F
Kornyshev, AA
Urbakh, M
Type
Journal Article
Abstract
Using molecular dynamics simulations, we study the impact of electrode charging and addition of solvent (acetonitrile, ACN) on structural forces of the BMIM PF6 ionic liquid (IL) confined by surfaces at nanometer separations. We establish relationships between the structural forces and the microscopic structure of the confined liquid. Depending on the structural arrangements of cations and anions across the nanofilm, the load-induced squeeze-out of liquid layers occurs via one-layer or bilayer steps. The cations confined between charged plates orient with their aliphatic chain perpendicular to the surface planes and link two adjacent IL layers. These structures facilitate the squeeze-out of single layers. For both pure IL and IL-ACN mixtures, we observe a strong dependence of nanofilm structure on the surface charge density, which affects the simulated pressure–displacement curves. Addition of solvent to the IL modifies the layering in the confined film. At high electrode charges and high dilution of IL (below 10% molar fraction), the layered structure of the nanofilm is less well defined. We predict a change in the squeeze-out mechanism under pressure, from a discontinuous squeeze-out (for high IL concentrations) to an almost continuous one (for low IL concentrations). Importantly, our simulations show that charged electrodes are coated with ions even at low IL concentrations. These ion-rich layers adjacent to the charged plate surfaces are not squeezed out even under very high normal pressures of ∼5 GPa. Hence, we demonstrate the high performance of IL–solvent mixtures to protect surfaces from wear and to provide lubrication at high loads.
Date Issued
2019-11-26
Online Publication Date
2020-10-28T07:00:19Z
Date Acceptance
2019-10-28
ISSN
0743-7463
Publisher
American Chemical Society
Start Page
15410
End Page
15420
Journal / Book Title
Langmuir: the ACS journal of surfaces and colloids
Volume
35
Issue
47
Copyright Statement
© 2019 American Chemical Society
Sponsor
The Leverhulme Trust
MIT-Imperial Seed Fund
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000500039900047&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
RPG-2016-223
Collaboration between the groups of Prof. M. Bazant at MIT and Prof. A. Kornyshev at Imperial College
Subjects
Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
ELECTRICAL DOUBLE-LAYER
MOLECULAR-DYNAMICS
ELECTROTUNABLE FRICTION
SOLVATION FORCES
CAPACITANCE
LUBRICANTS
WATER
ELECTROLYTES
ACETONITRILE
CONFINEMENT
Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
ELECTRICAL DOUBLE-LAYER
MOLECULAR-DYNAMICS
ELECTROTUNABLE FRICTION
SOLVATION FORCES
CAPACITANCE
LUBRICANTS
WATER
ELECTROLYTES
ACETONITRILE
CONFINEMENT
Chemical Physics
Publication Status
Published
Date Publish Online
2019-10-28