Solvent effects of 1-ethyl-3-methylimidazolium acetate: solvation and dynamic behavior of polar and apolar solutes

Abstract

We study the solvation properties of the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM](+)[ACE](-)) and the resulting dynamic behavior for differently charged model solutes at room temperature via atomistic molecular dynamics (MD) simulations of 300 ns length and 200 ns equilibration time. The solutes are simple model spheres which are either positively or negatively charged with a valency of one, or uncharged. The numerical findings indicate a distinct solvation behavior with the occurrence of well-pronounced solvation shells whose composition significantly depends on the charge of the solute. All the results of our simulations evidence the existence of a long-range perturbation effect in presence of the solutes. Our findings validate the dominance of electrostatic interactions with regard to unfavorable entropic ordering effects which elucidates the enthalpic character of the solvation process in ionic liquids for charged solutes.

The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood–Buff approaches

“…Thus, the heights of the maximum values are roughly comparable and bulk solution behavior can be observed for r ≥ 2.5 nm. In addition, it can be seen that the first peak in the cation-cation radial distribution function g ++ (r) is slightly higher than unity, which is a consequence of the strong cation-anion paring in the solution 44,121 . As a short preliminary summary, we can conclude that water has a negligible influence on the ion distribution and that the longer alkyl chain in BMIM does not significantly modify the results when compared to EMIM.…”

“…(9) up to a specific distance d, usually including the first solvation shell. Although a direct connection between the local/bulk partition coefficient and the KB theory is questionable 98 , a preferential exclusion or a preferential binding mechanism of species indeed can be detected 44,[99][100][101] . For instance, at short distances in the local region around the reference molecule, values of K p > 1 and K p < 1 indicate a preferential binding or a preferential exclusion behavior, respectively.…”

“…Accordingly, it is possible to deduce reliable results even from nonconvergent KB integrals. Specifically, for long-range ordered fluids like ILs 44 , the evaluation of these values is a challenging task. Fortunately, if the underlying radial distribution function g i j (r) is well-behaved at large distances, i. e. showing regulatory oscillations with approximately constant periods, the values of G i j (r) for r ≫ 1 nm oscillate around a constant number as well.…”

“…Hence, it is possible to compute different local/bulk partition coefficients in order to distinguish between cation and anion properties. Accordingly, the local/bulk partition coefficient provides a simple and reliable analysis tool for binding properties in computer simulations 44,47 .…”

“…Although it was shown that ionion interactions are not weakened in presence of residual water molecules 21 , it can be assumed that the presence of water has some impact on the general IL solvation behavior. For instance, a complex interplay between anion and cation solvation mechanisms was reported 34,44,[54][55][56][57][58][59][60][61][62][63][64] , implying that the presence of water seriously affects the corresponding solvation behavior. Although this is an important point, these effects have sparingly been investigated.…”