Pressure-induced relaxor-to-ferroelectric crossover in vinylidene fluoride relaxor terpolymer: A possible explanation to the high performance of the terpolymer nanocomposites

Understanding ferroelectricity in polymers presents a formidable challenge, as specific requirements in the crystalline ordering of the polymer chains must be met that run counter to the propensity of polymers to form largely disordered structures. Consequently, poly(vinylidene fluoride) (PVDF:[-CH₂-CF₂-]_n and its copolymers formed with poly(trifluorethylene) (PFTE:[-CHF-CF₂-]_n have been investigated very extensively because of their scientifically challenging and technologically important piezoelectric and ferroelectric (FE) properties. Early work has shown that irradiation (as well as the addition of 1, 1-chlorofluoroethylene (CFE) forming the terpolymers) irreversibly converts these FE copolymers to relaxors. In this presentation, we will recall some properties of the relaxor, and present experimental data obtained with the terpolymer under controlled hydrostatic pressure. We will show how the passage of the α conformation in the relaxor to the β conformation can be achieved by the application of stress. We will also show, that for terpolymer/nanocomposites (with graphene), some induced stress could be partially generated by the change of bipolar state ((terpolymer/ nanoparticles) subjected to an electric field) to a unipolar state due a possible ionization of the medium (high electronegativity of the Fluor). This stress leads to an induced relaxor to ferroelectric phase crossover at lower field.