A fundamental understanding of the dynamic properties of ionic liquids is an essential aspect for the application of these novel compounds. In the current work, molecular dynamics simulations were carried out to study the dynamic properties of a series of imidazolium based ionic liquids. Experimentally it has been observed that the substitution of a methyl group for a hydrogen at the C2 position of the cation imidazolium ring leads to an increase in the liquid phase viscosity, contrary to arguments that had been made regarding associations between the ions. The experimental trends in two pairs of ionic liquids were correctly captured by simulation and the origin of the effect was found to be entropic. On the other hand, the self-diffusivities were found to decrease with increasing alkyl chain length, which is likely due to the enthalpic effect. Further analysis reveals a linear relationship between ion self-diffusivity and the reverse of ion pair life-time. The same relationship was observed for other types of ionic liquids as well, suggesting a probably universal behavior and indicating an ion diffusion mechanism by ion pair forming and breaking in the ionic liquids.

Molecular dynamics studies of dynamic properties in ionic liquids

248th National Meeting (2014)

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