Electrocaloric Enhancement Induced by Cocrystallization of Vinylidene Difluoride-Based Polymer Blends

Active thermal control will be a major challenge of the twenty-first century, which has emphasized the need for the development of energy-efficient refrigeration techniques such as electrocaloric (EC) cooling. Highly polar semicrystalline VDF-based polymers are promising organic EC materials, however, their cooling performance, which is highly structurally dependent, needs further improvement to become competitive. Here, we report a simple method to increase the crystalline coherence of P(VDF-ter-TrFE-ter-CFE) terpolymer in the plane including the polar direction. This is achieved by blending P(VDF-ter-TrFE-ter-CFE) with minute amounts of P(VDF-co-TrFE) copolymer with similar VDF/TrFE unit content. This similarity allows for a cocrystallization of the copolymer chains in the terpolymer crystalline lamellae, preferentially extending the lateral coherence without lamellar thickening, as validated with a wide range of structural characterization. This trend results in a significant dielectric and electrocaloric enhancement, with a remarkable electrocaloric effect, ΔT_EC = 5.2 K, confirmed by direct measurements for a moderate electric field of 90 MV·m^-1 in a blend with 1 wt % of copolymer.