Thermoreversible gelation of poly(vinylidene fluoride)/poly(methyl acrylate) blends in diethyl azelate: a thermodynamic investigation

Abstract

The thermodynamic behaviour of poly(vinylidene fluoride) (PVF₂)/poly(methyl acrylate) (PMA) blend gels in diethyl azelate (DEAZ) was studied by differential scanning calorimetry at three different blend compositions (x^PVF₂ (weight fraction of PVF₂ in the blend) = 0.75, 0.5 and 0.25). Transmission electron microscopy together with optical microscopy indicate the presence of fibrillar network morphology in the gels. The quasi-binary phase diagrams drawn from both the heating and cooling processes are almost similar, with a hysteresis of 50-60 °C. The possibility of polymer-solvent compound formation in the blend gels have been explored from the composition dependency of enthalpy of gel fusion and enthalpy of gel formation data. Extending the procedure of the pure PVF₂/DEAZ gel systems to blend gels, it has been surmised that polymer-solvent compound formation also occurs in blend gels, but the stoichiometry of the complexes varies with blend composition. The shapes of the quasi-binary phase diagrams of the blend gels are different in some cases from that of pure PVF₂/DEAZ, gel indicating that the polymer-solvent compounds are incongruent or singular type depending on the blend compositions. A possible explanation for this behaviour has been offered from entropic and enthalpic viewpoints.