Influence of the alkyl side chain length on the thermophysical properties of chiral ionic liquids with a (1R,2S,5R)-(–)-menthol substituent and data analysis by means of mathematical gnostics

Abstract

A comprehensive physico-chemical characterization of the chiral ionic liquids of a 3-alkyl-1-[(1R,2S,5R)-(–)-menthoxymethyl]imidazolium bis(trifluoromethylsulfonyl)imides homologous series with a linear alkyl substituent ranging from the methyl up to the dodecyl group was carried out experimentally to investigate the way in which the measured thermophysical properties were influenced by the alkyl chain length on the cation. Refractive index, density, speed of sound, and isobaric heat capacity were measured as a function of temperature at atmospheric pressure and analyzed by methods based on mathematical gnostics. A robust linear regression along a gnostic influence function was used to optimize parameters of the relationships used in this work and to estimate the changing nanosegregation in the studied ionic liquid series by finding the Critical Alkyl Length Size (CALS) from heat capacity data. In addition, we propose the use of the marginal analysis to assess the quality of the measured data as an alternative to the estimate of the measurement uncertainty.