FWF P23494: Polarization forces in molecular ionic liquids
Prof. O. Steinhauser
Ass.-Prof. C. Schröder
03/2012 - 05/2017
187 k €
Molecular ionic liquids are molten salts with a melting point below 373 K. Most of them consist of a imidazolium based cation
and a weakly basic anion like triflate, dicyanoamide or bis(trifluoromethane)sulfonimide. Changing the cation or anion
respectively, one can generate a large diversity of physical properties.
Although remnant features of a charge ordered salt are visible, molecular ionic liquids show a translational and rotational dynamics
which is slower but comparable to that of neutral molecular liquids.
So far, the structure and single-particle dynamics of these systems was studied by simulations using pairwise additive forces.
They do not consider the response of the molecular charge distribution to the local environment.
This project tries to model the reorganisation of the charge distribution by atomic polarisation forces in three different ways:
The fluctuating charge model changes the atomic partial charges as a function of the molecular neighbourhood.
The induced-point-dipole method emulates the same effect by an auxiliary set of induced mathematical dipoles.
Drude oscillators work with physical dipoles which are represented by a pair of opposite auxiliary charges.
In a first project phase, we will evaluate the three models with respect to their efficiency, stability and reality in case of
molecular ionic liquids. With the most appropriate model at hand we will interpret, analyse and decompose the experimental
dielectric spectra for different cation-anion combinations. A special emphasis lies on the influence of the induced dipoles
and their coupling with the translational and rovibrational components. The last project phase is dedicated to the interpretation
of solvation dynamics of the model solute Coumarin as measured by the dynamics Stokes shift. Thereby, the mutual relation between
dielectric properties and solvation phenomena will be investigated in detail. The parameter-free Voronoi tessellation will be
used for the decomposition of various solvation properties into shell specific contributions.
In this way, the range of the solute's influence on the solvent ionic liquids can be rationalised.