abstract
High-precision heat capacities at 298.15 K of the [C(n)C(1)im][Ntf(2)] ionic liquid series were measured with an uncertainty of less than +/- 0.3%, using a drop heat capacity apparatus that was recently updated. The dependence of the c(p)(o) values on the alkyl side chain length for the extended ionic liquid series [C(n)C(1)im][Ntf(2)] (with n = 2 to 8, 10, and 12) displays a trend shift at [C(6)C(1)im][Ntf(2)], which is taken as an evidence for percolation limit. Above this limit there is an increase in the methylene group contribution to the molar heat capacity which is in agreement with the higher molar absolute entropies change observed from the (liquid + vapor) equilibrium results. The obtained experimental results support the model that the ionic liquids tend to be segregated into a polar network and non-polar domains, being followed by an increase of the entropy contribution of the non-polar domains. (C) 2012 Elsevier Ltd. All rights reserved.
keywords
CHAIN-LENGTH DEPENDENCE; IUPAC TECHNICAL REPORT; THERMODYNAMIC PROPERTIES; SMALL SAMPLES; 1-HEXYL-3-METHYLIMIDAZOLIUM; CALORIMETER
subject category
Thermodynamics; Chemistry
authors
Rocha, MAA; Bastos, M; Coutinho, JAP; Santos, LMNBF
our authors
acknowledgements
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. 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 Research Grants SFRH/BD/60513/2009. Thanks are also due to FCT for financial support for the project PTDC/CTM/103664/2008.