Data And QSPR Study For Viscosity Of Imidazolium-Based Ionic Liquids

Owing to some desirable properties, ionic liquids (ILs) have attracted increasing interests and applications in many domains. Unfortunately, however, they generally have much higher viscosities than conventional molecular solvents, which results to some problems of handling or transferring in chemical processing. ILs with lower viscosity are desired. Therefore, understanding the relationship between micro-structure and macro-viscosity along with a comprehensive viscosity data is important for the synthesis and rational design of ILs with low viscosity.In this work:1) A comprehensive database on viscosities of ionic liquids, which has been collected from 142 kinds of literature sources in the period from 1984 through 2009, was established. The cations and anions were named and ordered according to their molecular weight. There are totally 79 kinds of cations,71 kinds of anions and 1731 pieces of data.2) Based on our data base, we got the qualitative analysis of ionic liquid structure on the viscosity and found that the temperature, pressure, cation alkyl side chain on the cation C(2) position to replace the anion structure affect the viscosity;3) quantitative structure-property relationship (QSPR) study is performed for four selected data sets. The four correlations are obtained with R2>0.93, and quantum-chemical descriptors gave significant contributions. The cation-anion electrostatic interaction has the significant effects on the viscosity of imidazolium-based ILs, while other interactions (e.g., interionic hydrogen-bond, Van der Waals) or micro-characteristics (e.g., molecular orbital, electronic population, polarizability, volume, shape, branching degree, symmetry) also give some effects.4) Compared with the viscosity of organic matter, it can be found that the electrostatic interaction between ions is no longer the main factor affecting for the viscosity, hydrogen bonding and van der of force are even more prominent role. Ionic liquids is not only in common with ordinary organic compounds, but also have their unique.