(692f) Surfactant Self-Assembly in Ionic Liquids

Ionic liquids (IL) represent is a very attractive class of solvents due to their appealing physicochemical properties. These include thermal and chemical stability, negligible vapor pressure, high ionic conductivity and wide electrochemical window. In this work we study surfactant self-assembly in IL and the structure-property relationships for the shear rheology. Using a combination of experimental methods including rheology, cross-polarized light microscopy, and small angle neutron scattering, we characterized the phase diagram of the surfactant/IL model system: Cetyl trimethylammonium bromide (CTAB)/ethylammonium nitrate (EAN). The isotropic to hexagonal (I-H) transition occurred at remarkable high CTAB concentrations (~50 wt %). This transition is marked by an increase of up to three orders of magnitude in the elastic modulus; which results in a self-sustaining gel with a yield stress. The onset of the yield stress was temperature dependent and the I-H transition is perfectly reversible. These characteristics make this system very promising for applications where a combination of processability and stillness is crucial.