Physical pinning and chemical crosslinking-induced relaxor ferroelectric behavior in P(VDF-ter-TrFE-ter-VA) terpolymers

Abstract

Relaxor ferroelectric polymers, having a high energy storage density and efficiency, are rapidly developing for reliable and compact dielectric film capacitors. Until now, they have been based on highly fluorinated monomers lacking functionalities for further modifications, such as good dispersion of nanoparticles or facile crosslinking, to gain enhanced properties. In this work, we study the electroactive properties of a novel class of poly(vinylidene fluoride-ter-trifluoroethylene-ter-vinyl alcohol) (P(VDF-ter-TrFE-ter-VA)) terpolymers for capacitive energy storage applications. Additionally, we show that the VA units in these terpolymers can be crosslinked using facile urethane chemistry. It is found that introducing VA in the terpolymer backbone leads to cocrystallization with the fluorinated monomeric constituents. The VA defects promote the formation of TTTG monomer sequences favoring relaxor ferroelectric behavior. Consequently, the Curie transition is strongly reduced compared to P(VDF-co-TrFE) analogues. Moreover, chemical crosslinking of P(VDF-ter-TrFE-ter-VA) terpolymers results in extremely slim hysteresis loops due to the increase in the relative amount of the disordered paraelectric phase and ultrafine crystallites. Therefore, this new class of relaxor ferroelectric polymers, wherein physical pinning and chemical crosslinking are combined, shows great promise for future advanced applications.