Scott SHAW1, Colleen LASAR1, Andrew HORVATH1, Daniel RAUBER2, Frederik PHILIPPI3, Spyridon KOUTSOUKOS3, Tom WELTON3
1University of Iowa, Iowa City, United States
2Department of Chemistry, Saarland University, Saarbrücken, Germany
3Imperial College London, London, United Kingdom
Thin ionic liquid films can create ordered, liquid crystalline-like structures over distances of several micrometers. The maturation of anisotropic films to more ordered systems can take hours of time, and is thought to depend on the symmetry and intermolecular interactions of the IL ions. Here we report recent work to investigate the role of IL ion symmetry on self-ordering within the IL films. We report data for a series of six alkylimidazolium ILs paired with [TFSI]-. The lengths of the alkyl chains on the imidazolium cation range from 1 to 11 carbons with the most asymmetric being 1-methyl-3-undecylimidazolium bis(trifluoromethylsulfonyl)imide ([C1C11IM][TFSI]) and the most symmetric being 1,3-dihexylimidazolium bis(trifluoromethylsulfonyl)imide ([C6C6IM][TFSI]). Film properties were monitored using spectroscopic ellipsometry and infrared reflection absorption spectroscopy (IRRAS). We analyzed the vibrational mode over time, as the thin film matures, to deliver chemical insight into the maturation of the IL films. Our results show that viscosities (89.2 ± .03 cP to 124.7 ± .06 cP) appeared to have little effect on maturation of the films. However, our data suggest the more asymmetric cations lead to longer range ordering.