Participants: David Hoagland and Thomas McCarthy (coordinators) with Harry Bermudez, Shaw Ling Hsu, Alan J. Lesser, James J. Watkins; 3 graduate students

Ionic liquids (ILs) are described as salts that melt near or below room temperature. From the perspective of this Superseed, they are better described as ambient temperature solvents composed entirely of ions and thereby possessing unique properties. ILs serve to dissolve, swell, or wet polymers, generating new materials and shedding light on unresolved questions from polymer materials, especially those not addressable in the context of aqueous and organic solvents. Several distinguishing properties of ILs should be noted, including negligible volatility, high conductivity, persistence as liquids over an extreme temperature range, and widely tunable solvency (i.e., highly variable dielectric constant, hydrogen bonding, and ion pairing). With regards to solvency, many ‘intractable’ polymers such as cellulose and poly(vinyl alcohol) readily dissolve in ILs, enabling facile chemical functionalization that would otherwise be problematic in purely aqueous systems or impossible in organic solvents due to poor solubility. In addition to properties shared with conventional solvents, ILs display new properties. For example, as a strongly associated two-component liquid, ILs can separate into cationic and anionic domains of sizes similar to those of polymer coils. Moreover, one IL component may enrich at a liquid interface, altering the structure and properties of interfacially active polymers. IL properties depend critically on the identities of the cation and anion, and numerous new cationic/anionic IL pairings have been reported in the last decade, yielding a wide array of solvents with immense variation in properties.

Fig1. Receding contact line on an ultralyophobic surface. (a) Sketch of tensile breaking of capillary bridges; (b) SEM image of residual IL droplets on post tops; (c) SEM image of salt crystals left after water evaporation