Evidence of nanostructuration from the heat capacities of the 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid series


In the present work, the heat capacities at T = 298.15 K of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide, [C(N/2)C(N/2)im][NTf2], were measured, for the first time, using a high-precision heat capacity drop calorimeter, with an uncertainty of less than 0.15%. Based on the obtained results, it was possible to evaluate the effect of the cation symmetry on the heat capacity data through a comparative analysis with the [C(N-1)C(1)im][NTf2] ionic liquid series. The molar heat capacities of the [C(N/2)C(N/2)im][NTf2] ionic liquids series present a less pronounced deviation from the linearity along the alkyl chain length than the asymmetric based ionic liquids series. Lower molar heat capacities for the symmetric than the asymmetric series were observed, being this difference more evident for the specific and volumic heat capacities. As observed for the [C(N-1)C(1)im][NTf2] series, a trend shift in the heat capacities at [C(6)C(6)im][NTf2] was found that reflects the impact of nonpolar region nanostructuration on the thermophysical properties of the ionic liquids. The profile of the two regions is in agreement with the expected effect arising from the nanostructuration in ionic liquids. The results obtained in the present work show a clear indication that for the symmetric series, [C(N/2)C(N/2)im][NTf2], the starting of the liquid phase nanostructuration/alkyl chain segregation occurs around [C(6)C(6)im][NTf2]. (C) 2013 AIP Publishing LLC.




Chemistry; Physics


Rocha, MAA; Coutinho, JAP; Santos, LMNBF

nossos autores


Thanks are due to Fundacao para a Ciencia e Tecnologia (FCT), Lisbon, Portugal and to FEDER for financial support to Centro de Investigacao em Quimica, University of Porto through the project Pest-C/QUI/UI0081/2011, and CICECO, University of Aveiro, through the project Pest-C/CTM/LA0011/2011. Marisa A. A. Rocha acknowledges the financial support from FCT and the European Social Fund (ESF) under the Community Support Framework (CSF) for the award of a Ph.D. Research Grant No. SFRH/BD/60513/2009.

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