Impact of Pressure on the Dynamics of a Room Temperature Ionic Liquid

Room temperature Ionic liquids are considered promising electrolytes for electrical double layer capacitors because of their high thermal and chemical stability together with low volatility and large operational voltage window. Nano-scale structural heterogeneity of an ionic liquid arises from several interactions (chemical bonding and Columbic) among the constituent ions and impacts the microscopic dynamics. Use of extreme environmental conditions such as high pressure alters those interactions, which are linked to the functionality of ionic liquids. Here, we report the high pressure (up to 1.0 GPa) induced structure and dynamics change in a RTIL, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI), probed using x-ray and quasi-elastic neutron scattering techniques. The transition of the ionic liquid into the solid state at higher pressure and its return to the liquid state under decompression, associated with ions dimers formation, will be discussed.