Berlin 2015 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: Charged Soft Matter I

CPP 22.1: Vortrag

Dienstag, 17. März 2015, 09:30–09:45, PC 203

Dielectric properties of ionic liquids — •Grigory Zarubin and Markus Bier — Max Planck Institute IS and University of Stuttgart, Germany

The study of the dielectric properties of room temperature ionic liquids (RTILs) is an important task since RTILs are used as solvents in chemical reactions and the knowledge of their global solvation capability is crucial. Moreover, investigation of the dielectric properties, e.g. via the dielectric function ε (k), does not require sophisticated computer simulations on the atomistic level because one is concerned with the behavior of the system on large length scales. Thus, a coarse grained model of a dense fluid of charged hard spheres (restricted primitive model, RPM) is assumed to be sufficient. The dielectric properties of the ionic liquid model were investigated with the help of Monte Carlo (MC) simulations. The electrical susceptibility χ (k) = ε (k) − 1 has been calculated and it was assumed to have two constituents: i) χ_ind (k) corresponding to the induced charge polarization and ii) χ_orient corresponding to the orientation of effective dipoles formed by neighboring cation-anion pairs. The comparison of χ_ind and χ_orient showed that the ionic liquid is equivalent to a purely dipolar fluid for external static nonuniform electric fields of wavelengths λ ≤ σ with σ being the diameter of the cation (anion). An attempt to describe the orientational component χ_orient analytically in the framework of density functional theory (DFT) has been made. DFT within modified mean-field approximation is able to describe the computer simulation results quantitatively in the longwavelength limit (k → 0).