Dielectric Properties of Organic Solvents in an Electric Field

The effect of an external electric field (E) on the dielectric constant (epsilon) of several pure solvents [propylene carbonate (PC), ethylene carbonate (EC), acetonitrile (MeCN), and dimethyl carbonate (DMC)] and for several EC/DMC mixtures is explored using classical molecular dynamics simulation. Force fields were chosen that accurately predict the density and zero-field dielectric constant with respect to experiment. The simulation results for epsilon(E) for field strengths up to 0.4 V/angstrom are calculated and fit to the Booth model, which is a standard functional form for the dependence of the dielectric constant on electric field. For PC and DMC, the Booth model gives an excellent representation of the data at all electric fields studied. For EC and MeCN, the Booth model works well at lower field strengths (up to 0.15 and 0.2 V/angstrom, respectively), but at the higher electric fields, these systems are observed to crystallize, a phenomenon referred to as electrofreezing. This work will provide useful input data for the continuum modeling of devices, such as electric double-layer capacitors, that utilize organic electrolyte solvents.