Microstructural 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.