Structure and lifetimes in ionic liquids and their mixtures

Abstract

With the aid of molecular dynamics simulations, we study the structure and dynamics of different ionic liquid systems, with focus on hydrogen bond, ion pair and ion cage formation. To do so, we report radial distribution functions, their number integrals, and various time-correlation functions, from which we extract well-defined lifetimes by means of the reactive flux formalism. We explore the influence of polarizable force fields vs. non-polarizable ones with downscaled charges (±0.8) for the example of 1-butyl-3-methylimidazolium bromide. Furthermore, we use 1-butyl-3-methylimidazolium trifluoromethanesulfonate to investigate the impact of temperature and mixing with water as well as with the chloride ionic liquid. Smaller coordination numbers, larger distances, and tremendously accelerated dynamics are observed when the polarizable force field is applied. The same trends are found with increasing temperature. Adding water decreases the ion-ion coordination numbers whereas the water-ion and water-water coordination is enhanced. A domain analysis reveals that the nonpolar parts of the ions are dispersed and when more water is added the water clusters increase in size. The dynamics accelerate in general upon addition of water. In the ionic liquid mixture, the coordination number around the cation changes between the two anions, but the number integrals of the cation around the anions remain constant and the dynamics slow down with increasing content of the chloride ionic liquid.

Strong Microheterogeneity in Novel Deep Eutectic Solvents

“… Spatial distribution function in order to illustrate the side chain conformers. For each side chain series two examples are chosen, the one with C4 and C8.…”

“…are all very strong, because they exhibit an extremely directional behavior, i. e., angles a (ClÀ HÀ O) are close to 180 degrees and the peaks extend only to 165 degrees. This is different for aprotic ionic liquids, see for example [51,55,56], where usually such a directionaly cannot be achieved, because the donor atom often is a carbon atom. Furthermore, differences with respect to the chosen hydrogen bond and with respect to the different cations are too subtle to be discussed in details.…”

“…It is clear from these examples and from literature [18,21,[52][53][54] that the hydrogen bonds in the different DES . Spatial distribution function [43,51] in order to illustrate the side chain conformers. For each side chain series two examples are chosen, the one with C4 and C8.…”

A Theoretical Study on Trehalose + Water Mixtures for Dry Preservation Purposes

“…The kinetic properties of the different hydrogen bonds were analysed by using the reactive flux method by Gehrke et al [21] using the forward (hydrogen bond dissociation) and backward (hydrogen bond reformation) processes characterized by the corresponding lifetimes, τ f orward and τ backward . Therefore, the τ f orward can be considered to quantify the duration of the corresponding hydrogen bonds as well τ backward to measure the difficulties to form a new hydrogen bond after breaking.…”

A few key theoretical issues of importance in modern molecular electrochemistry

“…Indeed, almost all the concepts we use on everyday basis to analyze electrochemical data have been developed for simple electrolytes diluted in non-viscous solvent media. Hence, their very roots appear fully irrelevant to situations in which the medium itself is composed of organic bulky ions in close contact [35] in which high degrees of order are maintained over mesoscopic spatial scales [36].…”