Room temperature ionic liquids containing low water concentrations—a molecular dynamics study

Abstract

We have performed classical molecular dynamics to study the properties of a water-miscible and a water-immiscible room-temperature ionic liquid when mixed with small quantities of water. The two ionic liquids consist of the same 1-ethyl-3-methylimidazolium ([EMIM]) cation combined with either the boron tetrafluoride ([BF(4)]) or bis(trifluoromethylsulfonyl)imide ([NTf(2)]) anion. It is found that, in both ionic liquids, water clusters of varying sizes are typically hydrogen bonded to two anions with the cation playing a minor role. We also highlight the difficulties of obtaining dynamic quantities such as self-diffusion coefficients from simulations of such viscous systems.

Using a Combined Theoretical and Experimental Approach to Understand the Structure and Dynamics of Imidazolium-Based Ionic Liquids/Water Mixtures. 1. MD Simulations

“…However, a complex network of interactions among cations, anions and water molecules emerged from the analysis of the MD trajectories. Water molecules in [C 4 mim]Br/water mixtures were found to aggregate and form water clusters and a broad analysis of the molecular states of water has shown that, besides the existence of complexes between one water molecules and two Br − anions, previously pointed out also in other investigations of imidazolium-based ILs/water mixtures, 10,11,16,17,22 another significant state of water is the configuration in which a single water molecule interacts simultaneously with one Br − ion and with one imidazolium cation.…”

“…The water translational mobility is always higher than that of cations and anions, in agreement with previous MD investigations of imidazolium based IL/water mixtures. 10,13,20,63 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the cation one. 20…”

“…10,11,16,17,22 The results of our simulations show that anion...HOH...anion complexes are present also in [C 4 mim]Br/water mixtures, and in order to quantify this behaviour, the percentage of water molecules that are simultaneously bonded to two Br − 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ions has been calculated from the MD trajectories (see Figure 4). For the less diluted mixture the percentage is about 22% and decreases with increasing dilution, becoming negligible for the mixtures with IL/water molar ratio of 1:70 and 1:200.…”

Insight into the Intermolecular Interactions in [Bmim]BF4/[Amim]Cl−Ethanol−Water Mixtures by Near-Infrared Spectroscopy

“…1 To elucidate their heterogeneity, both experimental 2-32 and theoretical works [33][34][35][36][37][38][39][40] have shed light on the interactions between ILs and MS. However, it is worthy to note that most of these abovementioned works are limited to the simulations results, and/ or the measurement is only limited to the mixture of ILs and a small amount of MS. As mentioned above, ILs are highly ordered hydrogen bonded materials, and hydrogen bonding is most straightforwardly exhibited in IR or Raman spectra.…”

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

“…The outcomes of most studies revealed that low water concentrations induce the formation of residual water states in the IL 9,18 . Further studies highlighted that water molecules accumulate around the hydrophobic parts of the ions with a strong affinity towards the anions 29,30 . In agreement with previous results, it was reported that hydrophilic ILs show a tendency of pronounced water-anion network formation 31,32 and that even hydrophobic ILs attract high amounts of water 8,33 .…”