Thermodynamic and morphological analysis of eutectic formation of CBZ-l-Asp and l-PheOMe·HCl mixtures

The eutectic melting of a CBZ-l-Asp/l-PheOMe·HCl model mixture was investigated in kinetic, thermal, thermodynamic, rheological, and morphological aspects. From TX-phase diagrams, the eutectic composition was determined to be 0.55 M fraction of CBZ-l-Asp. The highest melting rate and the lowest apparent viscosity in the range of 55–75 °C were obtained at the eutectic composition. Using Arrhenius plots of melting rates and apparent viscosities, minimum activation energies in the range of 60–80 °C were obtained at the eutectic composition, whereas maximum values were attained below 60 °C. At the eutectic composition, the maximum heat of fusion, the lowest excess free energy, and the highest excess entropy values were observed by differential scanning calorimetry (DSC). A highly homogeneous morphology due to rearrangement of molecules was observed in the eutectic mixture via scanning electron microscopy and X-ray diffraction analysis. IR spectra revealed that hydrogen bonding in the mixture increases during eutectic melting.