Symmetrical ketone/n-alkane systems. 1. Phase diagrams from DSC

Binary phase diagrams have been determined for solution-crystallized sample s of two long-chain symmetrical ketones (kn) and n-alkanes (CII) with the s ame 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 fur K25/C25. They are found to form a solid solu tion which exhibits the solid-solid phase transition behaviors characterist ic of a crystal of the pure n-alkane component, when the molar fraction f(m ) of Kn 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 whi ch melts after a rather broad solid-liquid equilibrium at elevated temperat ures. 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 repr oducing the phase diagrams using the interaction parameter chi(12) between Kn and Cn molecules and discuss effects of solvent which Save rise to these anomalous phase behaviors in terms of chi(12) and chi(0i) (i = 1, 2) betwe en solvent and Kn (or Cn) estimated from their solubility curves.