564 - Ionic liquids in nanoconfinement

 Ionic liquids (ILs) are liquid salts composed solely of anions and cations. An extreme (conceptual) example of an IL would be to heat NaCl above ∼ 800 oC to achieve melting, whereby, unlike an ionic solution (e.g., NaCl in water), the NaCl will itself become liquid. 800oC seems an awfully high temperature for practical uses, but a range of other salts exist which are liquid at (or close to) room temperature, and the ‘IL’ terminology is restricted here to these.

ILs have practical applicability in a range of areas, including supercapacitors and lubri- cation. However, there are clear gaps in our understanding: As one example, the current ‘best’ supercapacitive device (where ‘best’ means the highest energy storage capacity per unit mass of electrode) discharges in ∼ 120 s – much longer than the fundamental expec- tation of τ = −RC ln(Vf /Vi) ∼ 2 s, where R and C are the resistance and capacitance, respectively, of a supercapacitor discharging from a potential of Vi to Vf . Another prime example is in lubrication, where alternating co/counterion layering is believed to reduce the effective viscosity by orders of magnitude.

The issues with ionic liquids are necessarily those of local rearrangement of anions and cations in (often) nano-confined geometries (e.g., nanopores are used in supercapacitors). Numerical work in the field is flourishing, but the only experiments with which they can be currently compared are macroscopic. The gap between micro- and macro- is too large, with experiments very rarely able to support or refute expectations. It in only very recently that surface force apparatus and frequency modulation atomic force microscopy have even begun to add information on the nanoscale, where the inherent nanoconfinement between the substrate and probe nicely maps that of the devices.

The colloquium intends to bring together researchers from groups in Europe working on ILs. The idea is to also bring in expertise from groups which presently do not work on ILs, but from whom we feel strong overlaps (either in fundamentals or in techniques) may be additive to the field. The goal is to allow for an exchange of ideas on the recent developments in the field and to share visions on its future.