Liquid Structure and Transport Properties of the Deep Eutectic Solvent Ethaline

Deep eutectic solvents (DESs) have emerged over the past decade as a potentially useful class of liquids for many applications including electrochemistry, synthesis, separations, and catalysis. DESs share many similarities with ionic liquids (ILs), in that they have very low volatility and vast chemical diversity. Although making generalizations about DESs and ILs is difficult because of their chemical diversity, many DESs are less expensive and have lower toxicity when compared to conventional ILs. One of the most commonly studied DESs is a 2:1 molar mixture of ethylene glycol (EG)/choline chloride (ChCl). This DES is commonly referred to as “ethaline” and is representative of a so-called “Type III” DES. Despite the increasing interest in ethaline in applications ranging from electrochemical synthesis and redox flow batteries to gas separations, there has been no neutron studies examining its structure and detailing the nature of its hydrogen bonding network. In the current study, 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 ethaline. 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 heterogenities resulting from hydrogen bonding interactions are quantified.