Ion dynamics in a highly compressed solution of tetra-ethylammonium – tetra-fluoroborate salt in propylene carbonate: A study in the equilibrium and glassy states

Abstract

Electrical conductivity of a solution of (Et4N+,BF4−) in propylene carbonate is measured by varying the pressure and temperature along different thermodynamic paths: pressure is increased from a low value in the liquid state up to ̴ 3.6 GPa well above the glass-transition pressure PG, along isotherms at temperatures between ̴ 295 K and ̴ 326 K. Up to a crossover pressure Pcross ̴ 1 GPa, the dc-conductivity decreases and obeys the Walden rule. Above Pcross, an anomalous pressure-dependence of the conductivity spectra is observed, leading to an increase in dc-conductivity up to PG. The dc-conductivity obeys density scaling, showing in the glassy state an exponential decrease against the scaling variable, independently of the thermobaric history of the sample. The conductivity spectra obey the time-temperature-pressure-superposition principle, therefore, the ion dynamics is not affected by the transition from the liquid state to the non-ergodic glassy state.