Enhanced Electrocaloric Response of Vinylidene Fluoride–Based Polymers via One‐Step Molecular Engineering

Abstract

Electrocaloric refrigeration is one of the most promising, environmentally-friendly technology to replace current cooling platforms-if a notable electrocaloric effect (ECE) is realized around room temperature where the highest need is. Here, we report a straightforward , onepot chemical modification of P(VDF-ter-TrFE-ter-CTFE) through the controlled introduction of small fractions of double bonds within the backbone that, very uniquely, decreases the lamellar crystalline thickness while, simultaneously, enlarging the crystalline coherence along the a-b plane. This increases the polarizability and polarization without affecting the degree of crystallinity or amending the crystal unit cell-undesirable effects observed with other approaches. Specifically, the permittivity increases by >35%, from 52 to 71 at 1 kHz, and ECE improves by >60% at moderate electric fields. At 40 C, an adiabatic temperature change >2 K is realized at 60 MVꞏm-1 (>5.5 K at 192 MVꞏm-1), compared to 1.3 K for pristine P(VDFter-TrFE-ter-CTFE), highlighting the promise of our simple, versatile approach that allows direct film deposition without requiring any post-treatment such as mechanical stretching or high-temperature annealing for achieving the desired performance. Enhanced Electrocaloric Response of Vinylidene Fluoride-based Polymers via One-Step Molecular Engineering

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

“…This cooling power is governed by the adiabatic temperature change, ΔTEC, of the active material, which corresponds to its temperature change upon application of a given value of electric field. 1,[3][4][5] ΔTEC depends on several material specific parameters, the main one of which is the polarization, P. A high maximum polarization Pmax is thus expected to enhance ΔTEC, and high change in polarization with field, (dP/dE),i.e. a high relative permittivity, εrensures the efficiency of the process by achieving this high ΔTEC at sufficiently low electric fields.…”

“…For semi-crystalline polymers such as highly-polar vinylidene difluoride-based (VDF) polymers, which have arisen as the main candidates for polymer-based solid state cooling, [4][5][6][7][8] both the permittivity and the polarization are highly structurally dependent. The structural parameters of their crystalline lamellae play an especially crucial role (Fig.…”

Tailoring fluorinated electroactive polymers toward specific applications

“…This augmentation of electroactive performance at low photoinitiator contents is mainly due to the introduction of double bonds on the polymer backbone as a side product of the functionalization reaction. Their impact on the electroactive properties has been shown to be pretty drastic with as much as 60% permittivity enhancement being achieved by double bonds alone [12]. Therefore, a general method to graft almost any functional group and thus induce a variety of different functionalities on FEPs was provided by this approach.…”

“…From an application standpoint, FEPs are encountered in some of the highest-end fingerprint sensors on the market. Their application though is not limited to that, as they are encountered in a plethora of devices that have not yet reached the mainstream markets including capacitors, memories [5,6], sensors [7,8], actuators [8,9], organic field effect transistors (OFETs) [10] and electrocaloric cooling devices [11,12] amongst many others.…”

Refrigeration through Barocaloric Effect Using the Spin Crossover Complex {Fe[H2B(pz)2]2(bipy)}

“…Various solid-state-caloric materials [1,2] have been studied to produce efficient refrigeration as alternatives to the harmful gases used in traditional non-energy-efficient refrigerators, based on the vapor-compression refrigeration cycle. Basically, these materials are able to change heat and temperature when submitted to an external field variation.…”