Heat capacities at 298.15 K of the extended [CnC1im][Ntf2] ionic liquid series

High-precision heat capacities at 298.15 K of the [CnC1im][Ntf2] 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 cpo values on the alkyl side chain length for the extended ionic liquid series [CnC1im][Ntf2] (with n = 2 to 8, 10, and 12) displays a trend shift at [C6C1im][Ntf2], 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.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► High precision heat capacities at 298.15 K of the [CnC1im][Ntf2] ionic liquid series. ► Interpretation of the nano-scale segregation or structural heterogeneity in ILs. ► A trend shift in the heat capacities with the cation alkyl chain starting at n = 6. ► Support of the percolation after a critical number of carbons n = 6 in the chain.