Effect of small amount of water on the dynamics properties and microstructures of ionic liquids

Abstract

A series of systems of 1‐butyl‐3‐methylimidazolium acetate ([Bmim][Ac]), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF4]), and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf2N]) with a small amount of water were simulated. Viscosities of systems were obtained by nonequilibrium molecule dynamics simulation and the results show that the viscosities change in different ways: for [Bmim][BF4] and [Bmim][Tf2N], viscosities decrease rapidly in the first stage, and then decrease slowly with the increase of water content. But for [Bmim][Ac], the viscosities increase first and then decrease. The unique phenomenon of [Bmim][Ac] can be attributed to the formation of chain‐like structure of anion•••water•••anion•••. Hydrogen bond (HB) interaction between ion pairs is weakened, but the number of HB between water and anions increases with increase of water content. Besides, the microstructures of water in ionic liquids‐water systems were compared and found that the distribution of water is more concentrated in [Bmim][Tf2N]‐H2O system, while it is isotropy in [Bmim][Ac]‐H2O system. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2248–2256, 2017

Insights into Ionic Liquids: From Z-Bonds to Quasi-Liquids

“…(d) The experimental and simulated viscosities of the IL–water mixture, where the top panel is BmimAc and the bottom panel is BmimBF 4 . Reproduced with permission from ref ( 102 ). Copyright 2017 Wiley.…”

“…However, our previous work has indicated that a small amount of water can unexpectedly increase the viscosity of Bmim acetate ( Figure 6 d). 102 The abnormal increase in the viscosity is attributable to a chainlike anion···water···anion cluster structure, where the chain length of the cluster increases with the IL concentration when the water content is less than 2%. The chainlike cluster does not disrupt the Z-bond within the ILs and can enhance the diffusive resistance, leading to a substantial increase in the viscosity.…”

“…High-precision and long-time-scale simulations are important for the design of ILs, especially quasi-liquid systems. Common force fields for the ILs are the molecular force field 40 , 53 , 102 , 157 , 180 and some polarizable force fields. 181 Although one can use such simulations to study the intrinsic bulk phase properties of ILs, obtaining an accurate description of the charge polarization and orientation of ILs on the solid surface remains challenging, especially for metal catalysts or charged electrode systems.…”

Revisiting Ionic Liquid Structure-Property Relationship: A Critical Analysis

“…In terms of interactions, there is a hydrogen bond (HB) weakening between ion pairs but However, there are some exceptions and [C 4 mim][Ac] viscosity shows a water content viscosity dependency. Initially, a small water amount (up to 0.02 wt%) induces an increase in the viscosity, which decreases with the increase in water addition [128]. By MD simulations, the authors attributed this anomalous behaviour to a water-induced structural change in the IL, with the formation of chain-like {anion•••water•••anion•••}n structure, which length increases with the water content up to 0.02 wt%.…”

Tracking the Micro‐Heterogeneity and Hydrogen‐Bonding Interactions in Hydroxyl‐Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study

“…Besides, ILs are also mixed with other molecular solvents to tune their properties and/or reduce costs [5] . It has been reported that a trace amount of water can dramatically alter the viscosity, resulting in significant changes in physicochemical properties [6] . Wang et al.…”