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

Binary phase diagrams have been determined for solution-crystallized samples of two long-chain symmetrical ketones (K n ) and n -alkanes (C n ) 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 f m of K n is lower than a critical value f m,c, being dependent on n . For f m > f m,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 f m > f m,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 χ 12 between K n and C n molecules and discuss effects of solvent which gave rise to these anomalous phase behaviors in terms of χ 12 and χ 0 i ( i = 1, 2) between solvent and K n (or C n ) estimated from their solubility curves.