Symmetrical Ketone/<i>n</i>-Alkane Systems. 1. Phase Diagrams from DSC

Abstract

Binary phase diagrams have been determined for solution-crystallized samples of two long-chain symmetrical ketones (Kn) and n-alkanes (Cn) with the same carbon numbers of n = 25 and 39 from differential scanning calorimetry (DSC) measurements. Toluene was used as the solvent for crystallization of K39/C39 samples and hexane for K25/C25. They are found to form a solid solution which exhibits the solid−solid phase transition behaviors characteristic of a crystal of the pure n-alkane component, when the molar fraction fm of Kn is lower than a critical value fm,c, being dependent on n. For fm > fm,c, K39/C39 samples have formed another type of solid solution which melts after a rather broad solid−liquid equilibrium at elevated temperatures. On the other hand, K25/C25 samples have given eutectic mixtures for fm > fm,c, and the phase diagram is found to agree with that of the same samples crystallized from melt. We apply the Flory−Huggins theory for reproducing the phase diagrams using the interaction parameter χ12 between Kn and Cn molecules and discuss effects of solvent which gave rise to these anomalous phase behaviors in terms of χ12 and χ0i (i = 1, 2) between solvent and Kn (or Cn) estimated from their solubility curves.