The Temperature Dependence of the Properties of Electrolyte Solutions. V. Determination of the Glass Transition Temperature and Comparison of the Temperature Coefficients of Electrolyte Conductance and Solvent Viscosity of Propylene Carbonate Solutions

Decoupling between the Temperature-Dependent Structural Relaxation and Shear Viscosity of Concentrated Lithium Electrolyte

The intermediate scattering functions of concentrated solutions of LiPF₆ in propylene carbonate (PC) were measured at various temperatures, two different wavenumbers, and three different concentrations using neutron spin echo (NSE) spectroscopy. The temperature dependence of the relaxation time was larger than that of the steady-state shear viscosity in all cases. The shear relaxation spectra were also determined at different temperatures. The normalized spectra reduced to a master curve when the frequency was multiplied by the steady-state shear viscosity, indicating that the temperature dependence of the steady-state shear viscosity can be explained by that of the relaxation time of the shear stress. It is thus suggested that the dynamics of the shear stress is decoupled from the structural dynamics on the molecular scale.

A Monte-Carlo simulation of ionic conductivity and viscosity of highly concentrated electrolytes based on a pseudo-lattice model

Simulating three transport phenomena-ionic conductivity, viscosity, and self-diffusion coefficient-in a common Monte-Carlo framework, we discuss their relationship to the intermolecular interactions of electrolyte solutions at high concentrations (C/mol l^-1 ∼ 1). The simulation is predicated on a pseudolattice model of the solution. The ions and solvents (collectively termed "molecules") are considered dimensionless points occupying the lattice sites. The molecular transport is realized by a repetition of swapping two adjacent molecules by the stochastic Gibbs sampling process based on simple intermolecular interactions. The framework has been validated by the fact that the simulated ionic conductivity and dynamic viscosity of 1:1- and 2:1-salts qualitatively well represent the experimental data. The magnitude of the Coulombic interaction itself is not reflected in the ionic conductivity, but the extent to which the Coulombic interaction is shielded by the dielectric constant has a significant influence. On the other hand, the dielectric constant barely influences the viscosity, while the magnitude of the Coulombic interaction is directly reflected in the viscosity.