Dual-Functional High-Entropy Polymer Exhibiting Giant Cross-Energy Couplings at Low Fields.

Abstract

A key component of cooling devices is the transfer of entropy from the cold load to heat sink. An electrocaloric (EC) polymer capable of generating both large electrocaloric effect (ECE) and substantial electroactuation can enable EC cooling devices to pump heat without external mechanisms, resulting in compact designs and enhanced efficiency. However, achieving both high ECE and significant electroactuation remains challenging. Herein, it is demonstrated that poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-double bond) [P(VDF-TrFE-CFE-DB)] tetrapolymers can simultaneously generate high electrocaloric effects and electroactuations under low fields. These P(VDF-TrFE-CFE-DB) tetrapolymers are synthesized through the dehydrochlorination of P(VDF-TrFE-CFE) terpolymer. By facile tuning the composition of the initial terpolymer to avoid pure relaxor state, tetrapolymers with optimal DB compositions are achieved, near the critical endpoint of normal ferroelectric phase with diffused phase transition. The nearly vanishing energy barriers between the nonpolar to polar phases result in a strong electrocaloric response and significant electroactuation. Specifically, the P(VDF-TrFE-CFE-DB) tetrapolymer exhibits an EC entropy change ΔS of 100 J kg^-1 K^-1 under 100 MV m^-1: comparable to state-of-the-art (SOA) EC polymers, while delivering nearly twice the electroactuation of the SOA EC polymers. This work presents a general strategy for developing EC materials that combine large electrocaloric effect and electroactuation at low electric fields.