Material propertiesMicrostructural variations of poly(vinylidene fluoride co-hexafluoropropylene) and their influence on the thermal, dielectric and piezoelectric properties

Polymer films and membranes of poly(vinylidene fluoride co-hexafluoropropylene), PVDF-HFP, have been prepared by thermally induced phase separation (TIPS), allowing the tuning of microstructure and morphology.The obtained microstructure is explained by the Flory-Huggins theory, depending on polymer concentration and solvent evaporation temperature. The formation of a porous membrane is attributed to a spinodal decomposition of the liquid-liquid phase separation. The effect of the processing conditions on the morphology, degree of porosity, degree of crystallinity and crystalline polymorph, thermal, dielectric and piezoelectric properties of the PVDF-HFP polymer were evaluated.The crystalline phase and degree of crystallinity depend on the processing conditions and further influence the dielectric and piezoelectric response. The piezoelectric coefficient is correlated with the β-phase content and decreases with decreasing polymer concentration in the initial solution at a given evaporation temperature.