Abstract
Ionic liquids (ILs) are a unique class of solvents with many potential applications, including absorption heating/cooling. Due to the large number of possible combinations of cations and anions, it is possible to tune the
IL to obtain the required properties for the application of interest. Many ILs are very hydrophilic, while even the
most hydrophobic ILs often absorb significant amounts of water. The presence of water in an IL can have a large
effect on the system properties. For instance, a small amount of dissolved water often leads to a dramatic reduction in the viscosity of the mixture. Dissolved water also affects the ionic conductivity of ILs and alters the solvation power of ILs for both polar and non-polar solutes. Knowledge of the phase diagram of these IL/water mixtures therefore is essential when designing absorption heating systems. Measuring isotherms often requires time consuming and/or expensive experiments, and does not necessarily lead to a deeper understanding of the molecular level interactions responsible for water-IL interactions. In contrast, molecular simulations are relatively inexpensive to perform, allowing one to screen potential ILs for a given application. Simulation also provides a detailed picture of how water and a given IL interact, thereby providing insight into ways of designing an IL to have a desired water solubility. Toward this end, atomistic-level Monte Carlo (MC) simulations have been performed to predict isotherms for a variety of IL/water mixtures. The simulations predict that exchanging some of the IL cations with a small metal cation can lead to an increase in the hydrophilicity of the IL, which impacts the capacity of the fluid and the enthalpy of mixing. Molecular dynamics simulations, which unlike Monte Carlo simulations capture timedependent properties, were also carried out to estimate the relative viscosities of the solutions.
