Room temperature ionic liquids (RTIL) are salts that are liquid at or near room temperature. Their negligible vapor pressure and other unique properties has stimulated a great deal of interest in their use as solvents, lubricants, and separation media. The use of RTILs in industry is hampered by the shortage of physical property data. Atomistic simulations provide a means for predicting the physical properties of these liquids, and can also shed light on the important chemical and structural features that lead to desirable properties.

Essentially all ILs are hygroscopic and therefore will contain significant amounts of water in most applications. It is known that the presence of water has a profound effect on the physical properties of ionic liquids. For example, it has been shown that very small amounts of water can significantly decrease the viscosity of ionic liquids. In this talk, we present the results of simulations in which the thermodynamic and transport properties of ionic liquid / water solutions are computed from atomistic simulations. We use a recently developed algorithm called Reverse Non-Equilibrium Molecular Dynamics (RNEMD) to compute the viscosity of ionic liquids as a function of water content and compare our results with experiment. We also show that water tends to form clusters in the ionic liquid, which changes the inherent structure of IL. This behavior leads to the observed changes in physical properties.