The importance of polarizability: comparison of models of carbon disulphide in the ionic liquids [C1C1im][NTf2] and [C4C1im][NTf2].

The local environment of CS2 and in solution in two ionic liquids ([C1C1im][NTf2] and [C4C1im][NTf2]) are investigated by atomistic simulation and compared with that in neat CS2. The intermolecular vibrational densities of states of CS2 are calculated and compared with experimental OHD-RIKES spectra. The fair agreement of the results from solutions but poor agreement of the results from neat CS2 suggest that while collective effects are unimportant in solutions, they have a major effect on the OHD-RIKES spectrum of neat CS2. Comparing polarizable and unpolarizable models for CS2 emphasizes the importance of polarizability in determining local structure.Support to ELQ was provided by the National Science Foundation under Grant CHE 1153077.This is the author accepted manuscript. The final version is available from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C6CP01752

Molecular origin of high free energy barriers for alkali metal ion transfer through ionic liquid–graphene electrode interfaces

In this work we study mechanisms of solvent-mediated ion interactions with charged surfaces in ionic liquids by molecular dynamics simulations, in an attempt to reveal the main trends that determine ion–electrode interactions in ionic liquids. We compare the interfacial behaviour of Li+ and K+ at a charged graphene sheet in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, and its mixtures with lithium and potassium tetrafluoroborate salts. Our results show that there are dense interfacial solvation structures in these electrolytes that lead to the formation of high free energy barriers for these alkali metal cations between the bulk and direct contact with the negatively charged surface. We show that the stronger solvation of Li+ in the ionic liquid leads to the formation of significantly higher interfacial free energy barriers for Li+ than for K+. The high free energy barriers observed in our simulations can explain the generally high interfacial resistance in electrochemical storage devices that use ionic liquid-based electrolytes. Overcoming these barriers is the rate-limiting step in the interfacial transport of alkali metal ions and, hence, appears to be a major drawback for a generalised application of ionic liquids in electrochemistry. Some plausible strategies for future theoretical and experimental work for tuning them are suggested

Hydrophobic solvation of Gay-Berne particles in modified water models.

The solvation of large hydrophobic solutes, modeled as repulsive and attractive Gay-Berne oblate ellipsoids, is characterized in several modified water liquids using the SPC/E model as the reference water fluid. We find that small amounts of attraction between the Gay-Berne particle and any model fluid result in wetting of the hydrophobic surface. However, significant differences are found among the modified and SPC/E water models and the critical distances in which they dewet the hydrophobic surfaces of pairs of repulsive Gay-Berne particles. We find that the dewetting trends for repulsive Gay-Berne particles in the various model liquids correlate directly with their surface tensions, the widths of the interfaces they form, and the openness of their network structure. The largest critical separations are found in liquids with the smallest surface tensions and the broadest interfaces as measured by the Egelstaff-Widom length

Hydrophobic solvation of Gay-Berne particles in modified water models.

The solvation of large hydrophobic solutes, modeled as repulsive and attractive Gay-Berne oblate ellipsoids, is characterized in several modified water liquids using the SPC/E model as the reference water fluid. We find that small amounts of attraction between the Gay-Berne particle and any model fluid result in wetting of the hydrophobic surface. However, significant differences are found among the modified and SPC/E water models and the critical distances in which they dewet the hydrophobic surfaces of pairs of repulsive Gay-Berne particles. We find that the dewetting trends for repulsive Gay-Berne particles in the various model liquids correlate directly with their surface tensions, the widths of the interfaces they form, and the openness of their network structure. The largest critical separations are found in liquids with the smallest surface tensions and the broadest interfaces as measured by the Egelstaff-Widom length