Simulation and Measurement of Water-induced Liquid-liquid Phase Separation of Imidazolium Ionic Liquid Mixtures

Final snapshots from molecular dynamics simulations showing the (a) dry [C2C1im] [OAc:TFSI] and (c) dry [C2C1im] [OAc:Cl] systems are miscible, but upon attaining x=0.83 (83 mol% water), the OAc:TFSI (b) system phase separates into water-rich and water-lean phases, while the OAc:Cl system (d) remains one phase. Each panel shows only [C2C1im] (cyan), [OAc] (blue), [TFSI] (grey), [Cl] (gold), or water (red).

Scientific Achievement

Computationally predicted liquid-liquid phase equilibrium confirmed by experimental measurements.

Significance and Impact

Electrolytes usually contain multiple components and the ability to predict the phase behavior would help with the design of electrolyte with desired properties.

Research Details

  • Molecular simulations predicted that the addition of water to the [C2C1im][TFSI]:[C2C1im][OAc] and [C2C1im][TFSI]:[C2C1im][Cl] mixtures would induce a liquid-liquid phase separation and that water addition to the [C2C1im][OAc]:[C2C1im][Cl] mixture would not produce a phase separation.
  • The effect of water on the phase behavior of the IL mixtures was verified experimentally, and the ionic liquid and water concentrations were determined in each phase.
  • Possible reason for color change observed in experiments was suggested based on simulation.

DOI: 10.1063/1.5054786

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