Deciphering the Stability of Porous Ionic Liquids: Flow Dynamics, Liquid Structure and Suspension Energetics

The rheological behavior of porous ionic liquids comprising ZIF-8 suspensions in two Newtonian ionic liquids – trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide and trihexyltetradecylphosphonium chloride – exhibited distinct and unexpected differences. ZIF-8 suspensions in the bis(trifluoromethylsulfonyl)imide-based liquid showed Bingham behavior with a measurable yield stress, whereas those in the chloride-based liquid remained Newtonian, even at high solid volume fractions of up to 17.4 %. Remarkably, the viscosities of these porous liquids were not significantly higher than those of the pure ionic liquids. While explaining these behaviours, we could elucidate how the stability and dynamic properties of porous ionic liquids are governed by the highly structured liquid phases, determined experimentally and using molecular dynamics simulations, and by the balance between particle-particle and ZIF-8-ionic liquid interactions, as evidenced by the heat effects measured during particle dispersion.