Experimental and theoretical description of low frequency viscoelastic behaviour in immiscible polymer blends

This work concerns a rheological and morphological study of blends of two immiscible polymers, polyethylene oxide and polyvinylidenefluoride-hexafluoropropylene. Melt blending was carried out in an internal mixer at 150 °C. The morphology was characterised through selective extraction and scanning electron microscopy observations. Rheological characterisation was performed with a constant stress rheometer in the linear viscoelastic regime. The storage modulus is studied vs. frequency in the whole composition range. At low frequencies and low volume fractions of the minor phase, the storage modulus G′ increases with the dispersed phase content. At higher concentrations of the minor phase, the behaviour of G′ vs. composition is modified. Plot of G′ at low frequency vs. composition clearly shows two different zones. The relationships between morphology and properties have been deeply studied and the observation of a maximum of elasticity is definitely related to the onset of co-continuity. A theoretical model is proposed to describe the different behaviours.