Intrinsic Electric Fields in Ionic Liquids Determined by Vibrational Stark Effect Spectroscopy and Molecular Dynamics Simulation

Abstract

The electric fields of ionic liquids are only slightly higher than those of common molecular solvents, and are strongly structure-dependent; they noticeably decrease with anion size because of increased separation of ions, and slightly decrease as the alkyl chain elongates due to increasing spatial heterogeneity. These were the key results of vibrational Stark effect spectroscopy and molecular dynamics simulations.

Insights on cholinium- and piperazinium-based ionic liquids under external electric fields: A molecular dynamics study

“…The effect of external EEFs on ionic liquids structuring depends on the values of intrinsic electric fields, E int , within the ionic liquids. Zhang et al 43 obtained the values of intrinsic electric fields in imizadolium-based ionic liquids for the first time by using vibrational stark effect spectroscopy and molecular dynamics simulation. These authors surprisingly showed that intrinsic electric fields in the studied ionic liquids are only slightly larger than in common molecular liquids.…”

“…They also showed a strong dependency of intrinsic electric fields on anion and cation structure, because of two main factors: (i) ions sizes, because of their effect on ions separation, and (ii) charge delocalization increasing intrinsic fields' intensity. 43 Therefore, the strengths of intrinsic electric fields leads to different intensities of EEFs required destroying the spatial heterogeneous arrangements for each ionic liquid. It has been showed that for the classic imidazolium-based ionic liquids, EEFs larger than 0.1 V Å −1 are required to modify the spatial structure.…”

A Critical Evaluation of Vibrational Stark Effect (VSE) Probes with the Local Vibrational Mode Theory

“…Given a simplified electrostatic description of non-covalent interactions between the vibrational probe and surrounding molecules, the strength of these intermolecular interactions can be assessed by the electric field a target chemical bond feels, as revealed by the VSE [5,13]. The VSE has been extensively applied to study the non-covalent interactions in different types of chemical systems and environments including proteins/enzymes [6][7][8]10,11,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], nucleic acids [34,35], ionic liquids [36,37], biological membranes [38], electrochemical interfaces/surfaces [12,[39][40][41][42][43], and polymers [3,44,45]. Recently, the range of applications has been extended to the investigation of water clusters [46,47] and molecular solids [48].…”

Phosphonium cation-based ionic liquids as neat lubricants: Physicochemical and tribological performance

“…The dependence of the conductivity with temperature is shown in Table 5. The strength of the formed field depends on ions interaction, especially by the size and structure of cation and anion [55]. Electric fields apparently decrease with increasing of cation size, due to the weakening of the electrostatic interaction and the depletion of the number of ions per volume [56].…”