Stretching-Induced Relaxor Ferroelectric Behavior in a Poly(vinylidene fluoride-co-trifluoroethylene-co-hexafluoropropylene) Random Terpolymer

Abstract

Relaxor ferroelectric (RFE) polymers exhibiting narrow hysteresis loops are attractive for a broad range of potential applications such as electric energy storage, artificial muscles, electrocaloric cooling, and printable electronics. However, current state-of-the-art RFE polymers are primarily poly(vinylidene fluoride-co-trifluoroethylene-co-X) [P(VDF-TrFE-X)] random terpolymers with X being 1,1-chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE). Potential dehydrochlorination at elevated temperatures can prevent the melt-processing of these Cl-containing terpolymers. It is desirable to achieve the RFE behavior for Cl-free terpolymers such as P(VDF-TrFE-HFP), where HFP stands for hexafluoropropylene. Nonetheless, HFP units were mostly excluded from the crystalline structure because of their large size, and thus no RFE behavior was observed when crystallized from the quiescent melt. Intriguingly, mechanical stretching could effectively pull the HFP units into the P(VDF-TrFE) crystals, forming nan...