Mixed crystals of n-alkane pairs A global view of the thermodynamic melting properties

The excess thermodynamic melting properties of the mixed crystalline rotator form of binary mixtures of neighbours and next-nearest neighbours of n-alkanes in the range C 11 H 24 to C 26 H 54 are characterized by a uniform temperature of enthalpy/entropy compensation of 320 K. Excess enthalpy differences have been obtained by microcalorimetry and excess Gibbs energy differences by phase diagram analysis and the two properties were combined to give the excess entropy differences. The excess enthalpy and excess entropy differences are negative and their absolute values, which are virtually equal to the excess properties of the rotator form, increase with increasing relative mismatch between the crystallographic unit cells of the two components involved.