Electrical Conductivities and Melting Points of Binary and Ternary Deep Eutectic Solvents via Molecular Simulation

Author: Gregory Opdahl, Department of Chemical and Biochemical Engineering

Mentor: Dr. Kenneth Benjamin, Department of Chemical and Biochemical Engineering

Solvent properties, such as electrical conductivity, are crucial to the successful design and operation of batteries. In several instances, the types of conventional solvents used in batteries are both potentially toxic to an individual, as well as to the environment. As an alternative, deep eutectic solvents (DES) are biologically based ionic liquid eutectic mixtures which possess tunable properties according to the selected cation, anion, and hydrogen bond donating co-solvent partner. These tunable properties include density, dielectric constant, and solvating power. DES possess extremely low vapor pressures, and therefore do not volatilize as easily as conventional organic solvents used in the pharmaceutical industry. Moreover, because DES are comprised of biologically based ions (i.e. choline) rather than synthetic ions (i.e. 1-ethyl-3-methyl-imidazolium), they are less toxic to organisms and the environment, and less expensive.

This work seeks to characterize environmentally benign, non-toxic, tunable DES through molecular simulation. In particular, molecular dynamics (MD) simulations are used to compute electrical conductivities for various binary and ternary DES, comprised of mixtures of choline chloride, urea, and glycerol. Electrical conductivities are calculated via post-processing of mean-squared displacement data from conventional MD simulations. The mean-squared displacement data will also be used to determine melting point ranges via changes in Arrhenius behavior across a large temperature span (100 Kelvin).

MD determined melting point temperatures and ranges will also be compared to the experimentally determined melting points/ranges. Comparisons of computed electrical conductivities for NaCl/H2O mixtures are presented for benchmarking against experimental data, along with new predictions for various binary and ternary DES. Comparison against electrical conductivities of conventional battery solvents are made as well to determine the feasibility of DES to become a more eco-friendly battery solvent alternative.