Macroscopic Differentiators for Microscopic Structural Nonideality in Binary Ionic Liquid Mixtures

Unraveling the Roles of Ionic Size and Hydrogen Bonding in Electric Field-Driven Ion Emission from Hydroxylamine Nitrate-Based Ionic Liquids

Ionic size and hydrogen bonding (HB) may play significant roles in controlling ion emission from HAN (hydroxylamine nitrate)-based ionic liquids (ILs) but have received little attention. In this paper, the ion emission behavior and mechanism in an external electric field are meticulously investigated using the molecular dynamics (MD) method and density functional theory. We find that the higher the proportion of ionic HAN in the blend of ILs, the longer the delay time of the ion start-up emission. In the positive mode, cations can evaporate directly from the surface of the studied ILs and manifest exclusively as the [EMIM]+ monomers within the simulation time scale, whereas in the negative mode, a variety of complicated anion clusters are emitted. As a result, the average charge-to-mass ratio of the positively charged species remarkably exceeds that of the negatively charged species. This large difference is attributed to the relatively larger size of the [EMIM]+ ion and the absence of substantial HB interactions between the [EMIM]+ ion and any other monomer, leading to diminished binding energies. Conversely, the strong HB interactions, primarily constituted by N-H--O and O-H--O hydrogen bonds, are clearly found in the [EtSO4]--based and HAN-based clusters. In addition, the [NO3]- and [EtSO4]- ions tend to combine with the small-sized [HA]+ ions to form large anion clusters rather than with the [EMIM]+ ions. The energy decomposition results further elucidate that the orbital interaction plays a pivotal role in the [NO3]- and [EtSO4]--based clusters. The findings clearly elucidate the experimental phenomena observed in previous studies and have implications for the formulation of multimode IL propellants.

The structural and hydrogen bonding properties of ionic liquid-co-solvent binary mixtures: the distinct behaviors of two anions

In practical applications, ionic liquids are often mixed with co-solvents. Understanding their structures and the interactions between them is a prerequisite for expanding their range of applications. In this work, spectroscopic and theoretical methods were employed to explore the structure and hydrogen bonding behaviors of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI)/1-ethyl-3-methylimidazolium thiocyanate (EMIMSCN) and co-solvents. It can be concluded that the hydrogen bonds associated with C2-H and C4,5-H are enhanced with the addition of co-solvents in the EMIMTFSI-DMSO system, while those associated with C4,5-H are weakened in the EMIMSCN-DMSO system. Infrared and excess spectra in the v(imidazolium C-H) range of EMIMSCN-CD3CN/CD3COCD3 systems further indicate that the abnormal change of hydrogen bonds associated with C4,5-H can be attributed to [SCN]-. These differences can be explained by the change of the primary interaction site. For EMIMTFSI, the primary interaction site in ion pairs and ion clusters is always C2-H, while for EMIMSCN, the primary interaction site in ion pairs is C2-H, and in ion clusters, it becomes C4,5-H. In the EMIMTFSI-DMSO system, the co-solvent primarily interacts with C4,5-H, while in the EMIMSCN-DMSO/CH3CN/CH3COCH3 systems, it primarily interacts with C2-H. In addition, several complexes are identified through excess infrared spectra and DFT calculations.

Hydrogen Bond Redistribution Effects in Mixtures of Protic Ionic Liquids Sharing the Same Cation: Non-ideal Mixing with Large Negative Mixing Enthalpies

We report a joint experimental and theoretical study characterising the hydrogen bond (HB) redistribution in mixtures of two different protic ionic liquids (PILs) sharing the same cation: triethylammonium-methanesulfonate ([TEA][OMs]) and...

Screening Ionic Liquids Based on Ionic Volume and Electrostatic Potential Analyses

Ionic liquids (ILs) are known to have tunable solvation properties, based on the pairing of different anions and cations, but the compositional landscape is vast and challenging to navigate efficiently. Some computational screening protocols are available, but they can be either time-consuming or difficult to implement. Herein, we perform a detailed investigation of the fundamental role of electrostatic interactions in these systems. We effectively develop a bridge between the previous volume-based approach with a quantum structure-property relationship approach to create fast, simple screening guidelines. We propose a new parameter that is applicable to both monovalent and multivalent ions, the ionic polarity index (IPI), which is defined as the ratio of the average electrostatic surface potential (V̅) of the ion to the net charge of the ion (q). The IPI correlation has been tested on a diverse data set of 121 ions, and reliable predictions can be obtained within a homologous series of IL compounds.