Locality and Fluctuations: Trends in Imidazolium-Based Ionic Liquids and Beyond

Abstract

Three different imidazolium-based ionic liquids, 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium thiocyanate, and 1-ethyl-3-methylimidazolium dicyanamide, are investigated by Car-Parrinello simulations. A common behavior, such as a broad electric dipole moment distribution of the ions and a related high degree of locality, is found to characterize all these systems. Going beyond imidazolium-based systems, we found that even for the protic ionic liquid monomethyl ammonium nitrate, the same features hold. These results represent a strong support to the hypothesis of rattling ions in long-living ion cages proposed in the last years.

Probing spatial locality in ionic liquids with the grand canonical adaptive resolution molecular dynamics technique

“…This kind of analysis would be extremely useful for designing ILs at the molecular level specified by clear structure-function relations. Our findings also strengthen the conclusions of previous theoretical work regarding the general local character in space of ionic liquids 19,53 . It suggests that by defining these spherical atomistically independent regions one can build physically well founded coarse-grained models of units larger than the molecular size and containing an entire group of anions and cations.…”

“…By calculating various radial distribution functions between anions and cations as a function of the size of the atomistic region and comparing them with the equivalent quantities in a full atomistic simulation we could conclude that even for a spherical region of radius 1.5 nm the atomistic degrees of freedom of the bulk do not play a relevant role. Our study can be seen in different perspectives (a) as a further argument that ionic liquids possess an inherent locality in the spatial structure, a hypothesis put forward in previous work 19,53 , and (b) as a modeling tool for designing ILs at the molecular level in the framework of structure-function relations. However, it must be underlined that our conclusions for other ionic liquids at this stage can only be qualitative and used a starting point for further studies.…”

“…Several computational studies have been carried out to characterize the locality in ILs, that is, how a molecule and its immediate surroundings respond to changes occurring on the global mesoscopic scale, e.g., the hydrogen bonding network of the bulk or other properties which typically occur on a larger scale 19,21,[23][24][25] . In particular, the structural locality and its relation to the governing interactions was actually either studied at a quantum level or at a coarse grained level.…”

Protic Ionic Liquids: Evolving Structure–Property Relationships and Expanding Applications

“…92 A computational investigation into the electrostatic properties of a few imidazolium AILs and the protic methylammonium nitrate indicated that they all had short ranged electrostatic interactions, with a broad electric dipole moment and large fluctuations, and did not find evidence of screening occurring on a molecular length scale. 94 …”

Ionic Liquids Treated within the Grand Canonical Adaptive Resolution Molecular Dynamics Technique

“…Atomic-level organization of ILs can be obtained by properly analyzing the structure factor and corresponding pair correlation functions including large scale correlation functions [21] of various components of ionic liquids. However, in our previous studies on ILs, we have shown that a large class of ILs can be characterized by a local scale where important properties that may be expected to be dominated by large scale pair correlations, are instead highly localized and depend only on the immediate neighboring molecules [22][23][24]. Motivated by these results, the adaptive resolution scheme (AdResS) [25,26] has been extended to grand canonical-like version [27][28][29][30] for the study of ILs.…”