Molecular Topology and Local Dynamics Govern the Viscosity of Imidazolium-Based Ionic Liquids

Ionic liquids (ILs) with branched alkyl chains were found to have higher viscosities than those with linear alkyl chains when the carbon numbers are the same. In addition, the branched chain IL with four carbons in the chain was found to have abnormally high viscosity. Our computational study revealed that the observed viscosities are caused by molecular structure.

Scientific Achievement

A direct connection between molecular structure and liquid viscosity was made, and the latter was explained based on the former feature.

Significance and Impact

The quantitative connection between molecular structure and liquid transport properties such as viscosity makes the accurate prediction of the liquid property possible, which will speed up the design process of new electrolyte systems.

Research Details

  • Using classical molecular dynamics (MD) simulations, the experimental trend in viscosity of two series of ionic liquids were reproduced.
  • Detailed analysis based on MD simulations reveals that the liquid viscosity is related to the packing structure in the liquid phase, which in turn is dictated by the molecular structure.
  • The abnormally high viscosity in one branched chain IL was found to be a result of the specific side chain length and molecular structure.

Work performed at University of Notre Dame (JCESR collaborator) and Texas Tech University by Y. Zhang, L. Xue, F. Khabaz, R. Doerfler, E.L. Quitevis, R. Khare, and E.J. Maginn. J. Phys. Chem. B, 2015, 119, 14934-14944

DOI: 10.1021/acs.jpcb.5b08245

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