Effects of Alkyl Chain Lengths and Isomers of Alcohols on the Phase Behavior of 1-Alkyl-3-methylimidazolium-Based Ionic Liquid + Alcohol Mixtures

Phase separation temperatures of alcohol mixtures of imidazolium-based ionic liquids (IL), 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C n mim][TFSA]) and 1-alkyl-3-methylimidazolium tetrafluoroborate ([C n mim][BF 4 ]), have been measured in order to elucidate the effects of alkyl chain lengths and isomers of alcohols on the phase behavior of IL + alcohol mixtures. The investigated IL + alcohol mixtures showed liquid–liquid upper critical solution temperature (UCST)-type phase behavior. The phase separation temperatures of IL + alcohol mixtures increased with elongation of the alkyl chain length of alcohol. The phase separation temperatures of IL + butanol mixtures were higher in the order of 2-methyl-1-propanol ( i -BuOH) ≈ 1-butanol (1-BuOH) > 2-butanol (2-BuOH) > 2-methyl-2-propanol ( t -BuOH). On the other hand, the isomerism effects of propanols on the phase separation temperatures were hardly observed. The UCSTs, T c, obtained from the phase separation temperatures decreased linearly with elongation of the alkyl chain length of ILs.