Vapor pressures of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with long alkyl chains
authors Rocha, MAA; Coutinho, JAP; Santos, LMNBF
nationality International
journal JOURNAL OF CHEMICAL PHYSICS
keywords AB-INITIO CALCULATIONS; VAPORIZATION ENTHALPIES; THERMODYNAMIC PROPERTIES; PHYSICOCHEMICAL PROPERTIES; CATION SYMMETRY; GAS-PHASE; LENGTH DEPENDENCE; SELF-AGGREGATION; CONDENSED STATE; VOLATILITY
abstract This work presents the vapor pressure at several temperatures for the 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide series, [C(N/2)C(N/2)im][NTf2] (N = 14, 16, 18, and 20), measured by a Knudsen effusion method combined with a quartz crystal microbalance. The thermodynamic properties of vaporization of the ionic liquids under study are analysed together with the results obtained previously for the shorter alkyl chain length [C(N/)2C(N/)2im][NTf2] (N = 2, 4, 6, 8, 10, and 12), in order to evaluate the effect of the alkyl side chains of the cation and to get additional insights concerning the nanostructuration of ionic liquids. The symmetry effect is explored, based on the comparison with the asymmetric imidazolium based ionic liquids, [C(N-1)C(1)im][NTf2]. A trend shift on the thermodynamic properties of vaporization along the alkyl side chains of the extended symmetric ionic liquids, around [C(6)C(6)im][NTf2], was detected. An intensification of the odd-even effect was observed starting from [C(6)C(6)im][NTf2], with higher enthalpies and entropies of vaporization for the odd numbered ionic liquids, [C(7)C(7)im][NTf2] and [C(9)C(9)im][NTf2]. Similar, but less pronounced, odd-even effect was found for the symmetric ionic liquids with lower alkyl side chains length, [C(N/2)C(N/2)im][NTf2] (with N = 4, 6, 8, 10, and 12). This effect is related with the predominant orientation of the terminal methyl group of the alkyl chain to the imidazolium ring and their influence in the cation-anion interaction. The same Critical Alkyl length at the hexyl, (C6C1 and C6C6) was found for both asymmetric and symmetric series indicating that the nanostructuration of the ionic liquids is related with alkyl chain length. (C) 2014 AIP Publishing LLC.
publisher AMER INST PHYSICS
issn 0021-9606
year published 2014
volume 141
issue 13
digital object identifier (doi) 10.1063/1.4896704
web of science category Chemistry, Physical; Physics, Atomic, Molecular & Chemical
subject category Chemistry; Physics
unique article identifier WOS:000343872800043
link 25296816
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journal impact factor 2.991
5 year journal impact factor 2.835
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