Quantitative analysis of the W-shaped excess heat capacities of binary liquid mixtures in the light of the local composition concept

A detailed analysis on the capability of the NRTL model to describe W-shaped excess heat capacities cpE of binary mixtures is presented. Both the classical and crossover renormalized versions of the model are used to correlate experimental data for various polar + alkane systems. The results are analyzed and discussed after a careful description of the fitting strategies. The classical version allows a good thermodynamic description far away from the critical point to be obtained. It also provides a significant insight into the relation of cpE and the non-randomness of the molecular distribution in the mixture. On the other hand, the crossover-renormalized version qualitatively represents the behaviour of cpE both near the critical point and away from it; however, it exhibits some deficiencies from a quantitative point of view.