Structure-Property Relationship for the Electrostrictive Properties of Ionic Liquids

Electrostrictive coefficients (γ) were computed for multiple ionic liquids (ILs) with molecular dynamics (MD) simulations. For ILs, γ quantifies the effect of an external electric field (EEF) expanding or contracting the IL. For all ILs studied, their molar volume increases once a strong EEF is applied. From these results, we derived structure-property relationships for the electrostrictive properties of ILs. The expansion is proportional to the applied EEF, dominated by the anion and inversely proportional to the molar volume of the IL. We rationalize the relationship with molar volume through the charge density of the ions in the IL. As molar volume increases across ILs, the charge density of a monovalent ion decreases, and charge becomes more delocalized. The decrease in charge density leads to a weaker coupling with the EEF, leading to ILs with high molar volume expanding less than ILs with low molar volumes.