Role of molecular complexation in solid-liquid phase diagram of poly-ethylene oxide/urea mixture

Publication date: 5 May 2017
Source:Polymer, Volume 116
Author(s): Guopeng Fu, Thein Kyu
Thermodynamic phase diagram of polyethylene oxide (PEO)/urea blend has been investigated with emphasis on the formation of induced crystals driven by molecular complexation. Of particular interest is that the complexed α crystal is more stable than those of neat constituents. The experimental solid-liquid phase diagram of PEO/urea blends has been analyzed in the context of the combined Flory-Huggins free energy for liquid-liquid demixing and phase field free energy of crystal solidification. The self-consistently calculated coexistence lines of the PEO/urea mixture exhibit an azeotrope type, accompanied by eutectoid reactions in the submerged regions, wherein the complexed α crystal decomposes into two coexistence crystalline phases. These coexistence crystalline phases were further analyzed by means of polarized optical microscopy, Fourier transform infrared spectroscopy, and wide-angle x-ray diffraction. A possible phase diagram of the complexed PEO/urea is constructed and discussed.

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