Yong ZHANG1, Daniel KIM1, Edward MAGINN1
1University of Notre Dame, Notre Dame, United States
Eutectic solvents are liquid mixtures formed when two solid components are mixed and their solid-liquid equilibrium leads to the formation of a eutectic with significant melting point depression. These mixtures are classified as “deep eutectic solvents” (DESs) when they exhibit significant deviation from thermodynamic ideality. DESs share many similarities with conventional ILs, but they often exhibit several advantages such as low cost, ease of synthesis and nontoxicity. Type III DESs, mixtures of hydrogen bond acceptors (HBAs) such as choline chloride (ChCl) and hydrogen bond donors (HBDs), have drawn extensive attention over the past two decades due to their potential for applications in a wide variety of fields. Depending on the structures of the HBD and/or HBA as well as the ratio of the two, the properties of the DESs can change significantly. It is essential to understand the structure-property relationship that can help explain how certain chemical and structural features lead to particular performance properties. This work takes as examples DESs formed by mixing ChCl and three similar di-alcohols, namely, ethylene glycol (EG), 1,2-propanediol (12PD) , and 1,3-propanediol (13PD). By changing the composition between HBA and HBD, the DESs formed by the three diols show different trends in ionic conductivity and viscosity. For example, with increasing ChCl composition, the viscosity of both ChCl/EG and ChCl/12PD increase monotonically whereas that of ChCl/13PD shows a minimum. To understand these trends, classical molecular dynamics simulations were carried out. To reproduce the experimental results over the wide HBA/HBD ratios, the classical force field was systematically optimized. Using the improved force field, various liquid structural and dynamic properties were calculated, and insight into the structure-property relationships of these mixtures was obtained.