Effects of polar compounds on the dynamics and dielectric properties of room-temperature ionic liquids

摘要

The scientific interest in room-temperature ionic liquids (RTILs) became extraordinarily high over the last two decades. While in the earlier days most of the studies focused on the synthesis and chemical properties, recently the interest in there physical, dynamical and structural properties is increasing. This thesis is aiming at the dynamical properties using dielectric relaxation spectroscopy. udThe first part of the thesis presents the development of new experimental routes and mathematical routines to record the dielectric spectra of liquids at microwave to far-infrared frequencies. udIt is followed by the discussion of the dielectric spectra of the neat, mainly imidazolium-based RTILs. Beside the extraction of the static dielectric constants, detailed information on the dynamics is obtained, including activation parameters. At room-temperature, the spectra are extended to terahertz and far-infrared frequencies, to cover the whole frequencies range relevant for intermolecular dynamics. Additional insight is gained by comparing these broadband spectra to molecular-dynamics simulations as well as to optical Kerr effect spectra.udFinally, binary mixtures of RTILs with polar solvents are investigated. The studies on mixtures with dichloromethane are indicating an expanded RTIL-like range, where the dielectric characteristics remain similar to the neat RTIL. Only at high dilutions, the mixtures behave rather like a conventional electrolyte solution with pronounced formation of contact ion-pairs. On the other hand the mixtures with water indicate a more complex, heterogeneous structure.ud