Large electrocaloric effect in ferroelectric polymers near room temperature.

Applying an electrical field to a polar polymer may induce a large change in the dipolar ordering, and if the associated entropy changes are large, they can be explored in cooling applications. With the use of the Maxwell relation between the pyroelectric coefficient and the electrocaloric effect (ECE), it was determined that a large ECE can be realized in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer at temperatures above the ferroelectric-paraelectric transition (above 70 degrees C), where an isothermal entropy change of more than 55 joules per kilogram per kelvin degree and adiabatic temperature change of more than 12 degrees C were observed. We further showed that a similar level of ECE near room temperature can be achieved by working with the relaxor ferroelectric polymer of P(VDF-TrFE-chlorofluoroethylene).

A dielectric polymer with high electric energy density and fast discharge speed.

Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density.

A modular approach to ferroelectric polymers with chemically tunable curie temperatures and dielectric constants.

We present a modular approach toward poly(vinylidene fluoride)-based ferroelectric fluoropolymers with high dielectric constants. This strategy is based on a two-step reaction, including the copolymerization of vinylidene fluoride and chlorotrifluoroethylene and a subsequent hydrogenation reaction. The chemical structures and compositions of the resulting polymers can be precisely controlled, leading to tunable Curie temperatures and dielectric constants and a systematical study of structure-property correlations.