Charcterization of the nature of interactions in ionic liquid co-solvent mixtures by dynamic light scattering (DLS)

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Within current research activities at SAOT and LTT in Erlangen, dynamic light scattering (DLS) from the bulk of fluids and the application of DLS to fluid surfaces, also called surface light scattering (SLS), is successfully used for the characterization of pure ionic liquids (ILs) as well as their mixtures with co-solvents. Besides offering a significant contribution to a reliable database, the determination of macroscopic thermophysical properties by DLS also provides a close insight into the bulk structure and the fluid structure at the phase boundary of IL co-solvent mixtures. Here, research activities which were already part of the second funding period of the DFG priority program “Ionic Liquids” (SPP 1191) should be continued and extended. Further selected imidazolium-based ILs and co-solvents which in particular show the tendency to strong hydrogen bonding should be investigated by DLS and/or SLS. An extension of the experimental methodology by contact angle measurements will allow a more detailed analysis of the molecular interactions present at the phase boundary of IL cosolvent mixtures. For DLS from bulk of fluids, all diffusion modes conceivable for IL cosolvent mixtures should be identified by the investigation of the scattered light over a wide range of scattering vectors or wave vectors. For SLS, the study of the scattered light over a wide range of wave vectors should point out the influence of the alkyl chain length on the damping of surface modes. Thus, information on the structure at the liquid surface is accessible, e.g., in form of the orientation of the alkyl chain of the cation.