Liquid Structure and Transport Properties of the Deep Eutectic Solvent Ethaline

Abstract

A range of techniques including physical property measurements, neutron scattering experiments, ab initio molecular dynamics, and classical molecular dynamics simulations are used to probe the structural, thermodynamic, and transport properties of a deep eutectic solvent comprised of a 1:2 molar ratio of choline chloride and ethylene glycol. This mixture, known as Ethaline, has many desirable properties for use in a range of applications, and therefore, understanding its liquid structure and transport properties is of interest. Simulation results are able to capture experimental densities, diffusivities, viscosities, and structure factors extremely well. The solvation environment is dynamic and dominated by different hydrogen bonding interactions. Dynamic heterogeneities resulting from hydrogen bonding interactions are quantified. Rotational dynamics of molecular dipole moments of choline and ethylene glycol are computed and found to exhibit a fast and slow mode.

Evolution of microscopic heterogeneity and dynamics in choline chloride-based deep eutectic solvents

“…There are some noted deviations between simulations and experiments, seen as a shoulder at 1 Å −1 and peak splitting between 2 and 4 Å −1 in simulated 33 mol%. This is attributed to Ch–Ch interactions and is due to the mixed deuteration state of the experimental choline, something that was seen in Ethaline structure factors of a previous work 34 . A key advantage of the simulated structure factors is the ability to decompose the total profile and isolate individual molecule–molecule and atom–atom interactions.…”

“…It has been reported that the DES Ethaline has a higher viscosity than the corresponding pure HBD, EG 46 , 47 , an opposite trend seen in Glyceline. In a recent study by Zhang et al 34 , it was found that the hydrogen bonds between Cl and EG are much stronger than those between EG molecules and it was believed that these stronger Cl–EG interactions cause the increase in viscosity upon the addition of ChCl to EG. This is supported by 1 H NMR data in Figure S13 as discussed earlier.…”

“…While a 0.7e scaling resulted in absolute bulk phase dynamics that were faster than experimental measurements, the correct physical trends were properly captured for the observed concentration and temperature range. The parameters used to describe ChCl and EG mixtures were detailed in our previous publication 34 . A 1 fs timestep, velocity Verlet integrator, periodic boundary conditions in all directions, cutoffs for LJ and Coulombic interactions of 12 Å, and a particle–particle particle-mesh long-range solver at 10 −4 accuracy were used for all simulations.…”

Computer Simulations of Deep Eutectic Solvents: Challenges, Solutions, and Perspectives

“…AIMD can also be applied to validate FFs for classical MD simulations [ 161 ]. For example, Jeong et al [ 141 ] utilized AIMD to develop atomistic polarizable FF for reline.…”

“…Most of the works on the structures of classical DESs are based on ChCl, such as reline [ 64 , 70 , 76 , 123 , 208 , 209 , 210 , 211 , 212 ] (HBD is urea), ethaline [ 161 , 210 , 213 , 214 ] (HBD is ethylene glycol), glyceline [ 82 , 210 , 215 ] (HBD is glycerol), and propoline [ 216 , 217 ] (HBD is propylene glycol). Over the last five years, their structures and properties have been investigated intensively and the main interactions have been determined.…”