Heterogeneity and viscosity decoupling in (acetamide + electrolyte) molten mixtures: A model simulation study

Recent time-resolved fluorescence experiments with (acetamide + electrolyte) melts have revealed pronounced decoupling of solute and solvent dynamics from medium viscosity. Here we examine the diffusion–viscosity (D–η) relationship by performing molecular dynamics simulations approximating acetamide molecules as dipolar Lennard–Jones (L–J) spheres and ions as L–J spheres with point charges. Interestingly, eventhough simulated viscosities are found to be approximately an order of magnitude lower than those from experiments, simulated diffusion coefficients are larger by ∼500–4000 times than the hydrodynamic predictions using the experimental viscosities. Simulated particle motions exhibit strong dynamic heterogeneity via pronounced non-Gaussian character of particle displacements. A signature of an extremely fast dipole orientation is also observed.