The QENS and MD simulations results for relaxation of the pure IL and the equimolar mixture with water probed by the dynamics of the C8mim hydrogen atoms in the time range of 2 ps to 1 ns are in excellent agreement. The QENS data show that translational relaxation increases by a factor of 7 on the addition of water, while rotational relaxation involving multiple processes fitted by a KWW function with low β values is speeded up by a factor of 3 on the time scale of the QENS measurements. The MD simulations show that the cation diffusion coefficient, inverse viscosity, and ionic conductivity increase on the addition of water, consistent with the very small change in ionicity. Difficulties in obtaining rotational and translational diffusion coefficients from fits to QENS experiments of ILs will be discussed [2].

[1] O. Borodin, D. L. Price, B. Aoun, M. A. González, J. B. Hooper, M. Kofu, S. Kohara, O. Yamamuro and M.-L. Saboungi, Effect of Water on the Structure of a Prototype Ionic Liquid, Phys. Chem. Chem. Phys 2016, 18, 23474−23481

[2] D. L. Price, O. Borodin, M. A. González, M. Kofu, K. Shibata, T. Yamada, O. Yamamuro and M. L. Saboungi, Relaxation in a Prototype Ionic Liquid : Influence of Water on theDynamics, J. Phys. Chem. Lett. 2017, 8, 715−719

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