Improved Force Field Model for the Deep Eutectic Solvent Ethaline: Reliable Physicochemical Properties

Abstract

In this work, we combined various parameters found in the literature for the choline cation, chloride anion, and ethylene glycol to set up force field models (FFMs) for a eutectic mixture, namely, ethaline (1:2 choline chloride/ethylene glycol (ChCl:2EG)). The validation of these models was carried out on the basis of physical and chemical properties, such as the density, expansion coefficient, enthalpy of vaporization, self-diffusion coefficients, isothermal compressibility, surface tension, and shear viscosity. After the initial evaluation of the FFMs, a refinement was found necessary and accomplished by taking into account polarization effects in a mean-field manner. This was achieved by rescaling the electrostatic charges of the ions based on partial charges derived from ab initio molecular dynamics (MD) simulations of the bulk system. Classical all-atom MD simulations performed over a large range of temperatures (298.15-373.15 K) using the refined FFMs clearly showed improved results, allowing a better prediction of experimental properties. Specific structural properties (radial distribution functions and hydrogen bonding) were then analyzed in order to support the adequacy of the proposed refinement. The final selected FFM leads to excellent agreement between simulated and experimental data on dynamic and structural properties. Moreover, compared to the previously reported force field model (Perkins, S. L.; Painter, P.; Colina, C. M. Experimental and Computational Studies of Choline Chloride-Based Deep Eutectic Solvents. J. Chem. Eng. Data 2014, 59, 3652-3662), a 10% improvement in simulated transport properties, i.e., self-diffusion coefficients, was achieved. The isothermal compressibility, surface tension, and shear viscosity for ethaline are accessed in MD simulations for the first time.

Atomistic Insight into the Electrochemical Double Layer of Choline Chloride–Urea Deep Eutectic Solvents: Clustered Interfacial Structuring

“…4,5,11,19 As a result, a number of fundamental studies have been carried out to rationalize the relationship between the structural organization of DESs (with emphasis on complexation) and melting point depression. 11,15,[29][30][31][32][33][34] In this regard, studies have shown that the strong intermolecular interaction between HBD and anions of hydrogen bond acceptor (HBA), i.e, the hydrogen bond network, is responsible for the disruption of long-range order anions-cations electrostatic interaction and low melting temperature at the compositions close to this of the eutectic mixture. 11,15,30,[33][34][35][36] However, despite a number of studies on the bulk structure and the dynamics and molecular interactions of DESs, the structure and behavior of their electrified interface is not yet clearly understood.…”

Modeling of Solid–Liquid Equilibria in Deep Eutectic Solvents: A Parameter Study

“…However, the ratio of constituents—i.e., the eutectic composition—is not as easy to determine as it is for ILs, in which the ratio of cations and anions is determined by mixture electroneutrality. Many molecular simulation studies can be found in the literature; these aimed to understand DES systems at the molecular level and determine their eutectic composition [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35]. It should be noted, however, that these studies were mainly performed using DESs of a fixed composition corresponding to a supposed hydrogen bond complex.…”

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

“…Most of the works on the structures of classical DESs are based on ChCl such as reline [47,53,59,106,[190][191][192][193][194] (HBD is urea), ethaline [145,192,195,196] (HBD is ethylene glycol), glyceline [65,192,197] (HBD is glycerol), and propoline [198,199] (HBD is propylene glycol). Over the last five years, their structures and properties have been investigated intensively and the main interactions have been determined.…”