Robustness of the Hydrogen Bond and Ion Pair Dynamics in Ionic Liquids to Different Parameters from the Reactive Flux Method

Abstract

Both hydrogen bonding and ionic interactions have an extreme influence on the properties of all kinds of materials. Ionic liquids mostly possess both of them. In the present work, we calculate with the aid of the reactive flux theory the dynamics of hydrogen bonds as well as of the ionic network for different 1-butyl-3-methylimidazolium-based ionic liquids. To apply this method, we carry out molecular dynamics simulations over broad temperature and simulation parameter ranges. Hydrogen bond lifetimes vary with temperature in the range of 10 ps (400 K)−60 ps (300 K) for the more fluid systems to 60 ps (400 K)−2000 ps (300 K) for the more viscous systems. The ion pair dynamics behave differently. While the more fluid systems show ion pairs which possess a factor of 4 longer lifetimes than the hydrogen bonds, the ion pair lifetimes of the more viscous systems actually are a factor of 0.6 smaller and thus faster than the hydrogen bond lifetimes. Although the choice of the hydrogen bond angle is less sensitive, a deviation in the distance criterion of up to 5% from the radial pair distribution functions' minimum leads to a change of less than 10% in the calculated lifetime. The ion pair dynamics are less sensitive with respect to the variation of the geometrical parameter. Interestingly, for both kinds of dynamics the impact on the activation energy is even less prone to the different cutoff values than the lifetime. In fact, the cutoff for the distance criteria causes the activation energies to remain almost unchanged. We find that the stability of the method is sufficient if the simulation time is at least a factor of 10 longer than the corresponding lifetime.

Water in Protic Ionic Liquid Electrolytes: From Solvent Separated Ion Pairs to Water Clusters

“…In Table 3 lifetimes of ions pairs and hydrogen bonds calculated using the reactive flux approach[ 79 , 80 ] were summarized. As expected, all exchange rates increase with increasing temperature.…”

“…Trajectory analysis was performed by TRAVIS [77,78] which allows for a wide variety of analyses to be performed from trajectory files. In this work, we evaluated radial distribution functions (RDFs), combined distribution functions (CDFs), diffusion coefficients and lifetimes using the reactive flux approach [79,80] …”

“…In this work, we evaluated radial distribution functions (RDFs), combined distribution functions (CDFs), diffusion coefficients and lifetimes using the reactive flux approach. [ 79 , 80 ]…”

Assessing the Structure of Protic Ionic Liquids Based on Triethylammonium and Organic Acid Anions

“…It is clear that the limits of our simulations are to be found in the short times that, besides equilibration of reaction 1 , are largely insufficient to reliably evaluate the frictional properties of the fluids such as viscosities or diffusion coefficients. 39 …”

Hydrogen Bonding and Vaporization Thermodynamics in Hexafluoroisopropanol‐Acetone and ‐Methanol Mixtures. A Joined Cluster Analysis and Molecular Dynamic Study

“…From an experimental prospective, hydrogen bonds can be investigated via IR and NMR [22,23] . However, since their experimental detection and analysis can still be challenging and expensive, computational tools may be valuable for this kind of investigation [24–26] . We were able to calculate the activity coefficients of methanol in its binary mixtures with a set of small alcohols, which allowed some insight into how the chain length and branching modify the hydrogen bond network and consequently affect their behavior [27] .…”