(360ao) Elucidating the Bulk and Interfacial Structure of Ionic Liquids from the Dilute to Concentrated Regimes Using Molecular Dynamic Simulations

Ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4), have been scrutinized as viable electrolytes for electrochemical reactions due to their highly tunable cation/anion properties, intrinsic conductivity, wide electrochemical stability window, low volatility, and strong electrostatic interactions. While these features make ILs promising, the molecular-scale structure of ILs in bulk solution and near electrochemical interfaces remains poorly understood, inhibiting the rational application of ILs for electrochemical reactions. To address this gap, molecular simulations can be utilized to study the dynamic nature of IL structure that is difficult to observe in experiments, especially as a function of concentration and near the electrode surface. In this work, we performed atomistic molecular dynamics (MD) simulations to quantify concentration-dependent changes in EMIM-BF4 structure in solvents including acetonitrile, dimethyl sulfoxide, and propylene carbonate and determine how interactions between the IL and solvent impact structure. We show that EMIM-BF4 exhibits variations in the tendency to form molecular-scale clusters as a function of concentration ranging from dilute to neat regimes. We further parameterized descriptors of ILs for physiochemical property prediction related to IL structural clustering and report variations in structural parameters induced by the presence of an interface. These quantitative metrics will permit analysis and understanding of how IL structure impacts electrochemical reactions, which is necessary for fine-tuning electrolyte properties for these systems.