Scott SHAW1, Andrew HORVATH1, Colleen LASAR1, Radhika ANAREDY1
1University of Iowa, Iowa City, United States
The molecular ordering of (a)symmetric ionic liquids can develop spectroscopic signals to allow tracking phase transitions and intermolecular interactions. This presentation will show recent work to investigate the role of IL ion symmetry and co-solvents on self-ordering within the liquid bulk phase and thin (micrometer thick) films. We report data for two groups of ILs, phosphonium Alkyl with BCN4, phosphonium ether with BCN4, and a series of six alkyl-imidazolium ILs paired with TFSI anion. The lengths of the alkyl chains on the imidazolium cation range from 1 to 11 carbons long 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 are monitored using spectroscopic ellipsometry and infrared reflection absorption spectroscopy (IRRAS). We also use differential scanning calorimetry coupled with variable temperature infrared spectroscopy to study phase transitions and structural changes of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]) mixed with water or acetonitrile as a function of temperature. Our results show how anion polarity and presence of hydrogen bonding affect the system’s behavior. As the ILs are diluted with water or acetonitrile cosolvents, our results show significant changes in phase transition enthalpies and shifts in phase transition temperatures, as well as new phase transitions not observed in neat IL nor neat cosolvent.