Ionic Liquid Structure in Thin Films

Abstract

Room Temperature Ionic liquids present an exciting opportunity to examine surface confined thin fluid films and extended interfacial systems that may prove useful for electrochemical applications. This work explores the behavior of thin (1-5000 nm) films and bulk RTIL interfaces in contact with air and silver metal surfaces. Thin films are introduced by a highly controlled dynamic wetting process. Bulk interfaces are prepared by immersing the metal electrode into an IL solution. Data from ellipsometry, vibrational spectroscopy, contact angle, and electrochemical measurements are reported for a series of Cn-3-methylimidazolium based liquids with varying length alkane tails. Results correlate chemical nature of the liquid and substrates with resulting molecular structure of the interface and behavior of the wetting film. Descriptors include chemical interactions i.e. hydrophobic forces, hydrogen bonding, van der Waals, electrostatics, etc.

Structure and Nanostructure in Ionic Liquids

“…The static and dynamic structures of thin films of AILs adjacent to various substrates including mica, − silica, silver, , Au(111), , Ni(111), Pd(111), , and Al 2 O 3 /NiAl­(110) have been reported. The structure present was characterized using many surface-specific techniques and some vacuum based-techniques, for example, reflection–absorption infrared (RAIRS) or angle resolved XPS spectroscopy, spectra of the latter made possible due to low IL vapor pressures…”

Solvents and Stabilization in Ionic Liquid Films

“…Finally, previous work from our group has shown that the substrates are sufficiently smooth to treat the boundary layer as static. , Some ILs are non-Newtonian fluids and are not necessarily expected to follow the Landau–Levich model. Their physicochemical properties that lead to deviations from this model are fundamentally interesting. ,,,− The work presented here aims to determine how mixing ILs with traditional Newtonian molecular solvents, e.g., water and acetonitrile, affects these physicochemical behaviors. We are particularly interested in the thin film structure as it includes the “interfacial” and “bulk” phases and the dynamics of the IL system converting between these two phases. …”

“…Their physicochemical properties that lead to deviations from this model are fundamentally interesting. 39 , 42 , 43 , 47 − 49 The work presented here aims to determine how mixing ILs with traditional Newtonian molecular solvents, e.g., water and acetonitrile, affects these physicochemical behaviors. We are particularly interested in the thin film structure as it includes the “interfacial” and “bulk” phases and the dynamics of the IL system converting between these two phases.…”

“…Wetting experiments are performed using an air-tight PTFE cell and motor assembly described previously. , Briefly, the disk-shaped metallic substrates are rotated at varying velocities through a fluid droplet dispensed by a glass capillary. This causes a fluid film to be extruded onto the reflective substrate.…”