Theoretical Study On The Microstructure Of Binary Mixtures Composed Of The [C₂mim][Tf₂N] And Water,Methanol,Ethanol

Ionic liquids?ILs?ars highly favored for chemical reactions and separations due to their unique chemistry and physical properties.During the last few decades,the study of ionic liquids have also grown significantly,especially about the mixtures of ionic liquids.Mixtures are not only functional designing much easier than pure ILs but also widening the applications of ILs.Complex intermolecular interactions in ILs may make it difficult to interpret the structures at the molecular level.Not all ILs can exhibit ideal characteristics,so even a small number of possible cation-anion combinations are hard to apply to practical applications.Therefore,molecular-based understanding and evaluation of possible ionic liquids is critical to the use of these materials in different fields.MD simulations were performed to investigate the structures and some dynamic properties of binary mixtures of 1-ethyl-3-methylimidazolium bis?trifluoromethyl sulfonyl?imide?[C₂mim][Tf₂N]?and water,methanol,ethanol.By processing the data obtained after the simulations,the influence of the chemical structure of the IL and of the concentration on the evolution of the microstructure of the mixtures?radial distribution functions,hydrogen bonding,coordination numbers?was analyzed to learn further about the microscopic properties of the binary systems.In aqueous binary system,the addition of a small amount of water does affect the interaction of anions and cations in the IL,but this effect is essentially negligible.Water in the mixed system mainly forms hydrogen bonds with oxygen atoms on the anions,destroying the interaction between the anions and the cations.When the water content is large,[C₂mim][Tf₂N]is rapidly saturated,and the excess water molecules self-aggregate into a larger cluster structure.The state of methanol and ethanol in mixed systems is similar to that of water.There are two main types:forming hydrogen bonds with itself or forming hydrogen bonds with anions in IL.[Tf₂N]^-has four S=O groups that can provide four hydrogen bond acceptors.The imidazolium cation occupies a position through the hydrogen atom on the ring,and the remaining three acceptors form hydrogen bonds with the alcohol molecules,and the alcohol-alcohol clusters begin to form.As the concentration of alcohol increases,more and more alcohol molecules accumulate around the anions.Gradually,the aggregation of alcohols reaches the limit of anions hydrogen bond saturation.After a certain key point,the alcohol-alcohol interaction predominates and the mixed system is closer to the pure alcohol system.Through the study of the properties of the microstructure of the binary system of ionic liquid and water or alcohol,it is expected to be guided by experiments,such as accurately determining the key points,and preparing for the catalyst carrier and chemical separation in the future.