(346ae) Utilization of Molecular Dynamics to Predict Glass Transition Temperatures of Imidazolium-Based Ionic Liquids and Their Mixtures

The inherent characteristics of ionic liquids make them popular candidates as electrolyte solutions, and their properties are also easily tunable via selection of constituent ions for desired applications. When designing ionic liquid-based electrolytes, the glass transition temperature of the solution is taken into consideration as it determines the operating temperature window while also correlates with key transport properties such as viscosity and conductivity. Identifying and predicting the glass transition temperature of ionic liquids and their mixtures can aid in expanding the design, optimization, and implementation of their use. In this study, we report a method to predict the glass transition temperature of ionic liquids, 1-propyl-3-methylimidazolium iodide and 1-butyl-3-methylimidazolium iodide, and their mixtures with water and gamma-butyrolactone, respectively, by utilizing molecular dynamics (MD) simulations. Annealing simulations over a temperature range of 500K to 100K are performed to effectively capture the glass transition phase. The potential energy of each system is monitored to reveal variations in behavior that could indicate a glass transition temperature. Initial results suggest that parameters such as simulation box size and cooling rate may have a significant impact on the capability to successfully predict the glass transition temperature. To understand underlying molecular interactions, radial distribution functions are computed at varying temperatures. Other properties including self-diffusion coefficients and densities are also calculated to check for observable changes near the glass transition temperature. The simulation results are complemented by experimental characterization methods, including dynamic differential calorimetry (DSC) and environmentally controlled rheology, to validate and further improve this reported computational method in predicting the glass transition temperature of ionic liquids and their mixtures with cosolvents.