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

Area of Science:

• Materials Science
• Thermodynamics
• Polymer Chemistry

Background:

• Entropy transfer is crucial for cooling device efficiency.
• Electrocaloric (EC) polymers offer potential for compact, efficient cooling by combining electrocaloric effect (ECE) and electroactuation.
• Simultaneously achieving high ECE and significant electroactuation in EC polymers is a persistent challenge.

Purpose of the Study:

• To develop novel electrocaloric polymers capable of high electrocaloric effects and electroactuation under low electric fields.
• To investigate the relationship between polymer composition, phase transitions, and combined EC and actuation performance.
• To present a general strategy for designing advanced EC materials.

Main Methods:

• Synthesis of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-double bond) [P(VDF-TrFE-CFE-DB)] tetrapolymers via dehydrochlorination of a precursor terpolymer.
• Tuning the composition of the terpolymer to achieve optimal tetrapolymer properties near a diffused ferroelectric phase transition.
• Characterization of the electrocaloric effect (entropy change) and electroactuation performance under varying electric fields.

Main Results:

• P(VDF-TrFE-CFE-DB) tetrapolymers exhibit simultaneous high electrocaloric effects and electroactuation under low electric fields.
• An EC entropy change (ΔS) of 100 J kg⁻¹ K⁻¹ was achieved at 100 MV m⁻¹, comparable to state-of-the-art EC polymers.
• The synthesized tetrapolymers delivered nearly double the electroactuation compared to existing state-of-the-art EC polymers.
• Optimal tetrapolymer compositions were found near the critical endpoint of the normal ferroelectric phase, characterized by diffused phase transitions and minimal energy barriers.

Conclusions:

• The developed P(VDF-TrFE-CFE-DB) tetrapolymers represent a significant advancement in electrocaloric materials.
• These materials enable efficient heat pumping for cooling devices without external mechanical components.
• The study provides a viable strategy for designing EC materials with combined large electrocaloric effect and electroactuation at low electric fields, paving the way for next-generation cooling technologies.