Self assembly, dynamics and charge transport in bulk ionic liquids and ionogels

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Ionic Liquids (ILs), i.e. molten salts that are liquid at room temperature, are liquids with unusual properties that have many potential applications, e.g. in what is known as "green chemistry" or in energy applications. Many ionic liquids, due to their amphiphilic molecular architecture, tend to show self-assembly and structure formation on the mesoscale (i.e. formation of polar and apolar domains), which influences molecular dynamics and ion transport in these materials. It is the aim of the current project to understand, how charge transport and molecular dynamics depend on the ionic liquid mesostructure, with particular emphasis on coupling/decoupling phenomena of charge transport and structural relaxation in these systems.Therefore in this project a series of Ils with varying tendency to form polar/apolar domains is investigated (realized, e.g. by varying the alkyl chain length of a cation or by addition of small amounts of solvents) with respect to molecular dynamics and ion transport. In the next step it is planned to investigate Ils in ionogels. The latter systems are based on ionic liquids by adding various network forming agents. In these materials high conductivity is often combined with almost solid-like mechanical properties, which makes them particularly interesting for many applications. In the ionogels the effect of inner surfaces on the IL structure formation and on dynamics and charge transport are to be clarified. In particular, interesing effects are expected when the length scale of geometric confnement by the network forming agent meets the lengthscale of domains and aggregates in the IL. In terms of experimental method, the emphasis in the current project is on depolarized dynamic light scattering, which unambiguously identifies molecular reorientation and is not influenced by charge transport or polarization effects. A combination of different light scattering techniques (photon correlation, Tandem Fabry Perot and Raman spectroscopy) allows us to cover the full relevant spectral range, between 1 mHz up to about 10 THz. At the same time broadband dielectric spectroscopy (between 1 Microherz and 50 GHz) will provide information on the charge transport in the system. In that way it will be possible to unambiguously separate molecular dynamics and charge transport. The temperature dependent domain structure in the ILs will be monitored by small angle scattering techniques. Therefore, we expect to improve our understanding of the interrelation of structure formation, dynamics and charge transport in ILs and in ionogels, which, on the long run, will help to realize knowledge-based material design with ionic liquids.