Limiting Relative Permittivity “Burn-in” in Polymer Ferroelectrics via Phase Stabilization
Résumé
VDF-based polymers, such as poly(vinylidene fluoride) (PVDF) and its copolymers, are well-known ferroelectrics of interest for numerous applications, from energy storage to electrocaloric refrigeration. However, their often complex thermal phase behavior that typically leads to a low phase stability can drastically affect the long-term dielectric properties of this materials family. Here, we demonstrate on the example of the ter-polymer P(VDF-ter-TrFE-ter-CFE) (molar ratio: 64/29/7) that by limiting mass transport/segmental chain-motion both during solidification and in the solid state, a drastically smaller 'burn-in' in relative permittivity, εr, is observed. Indeed, εr decreases little over time and saturates rapidly at 96-97% of its initial value. Mass transport thereby is manipulated by controlling the number of chain entanglements per macromolecule, achieved via selection of a suitable polymer solution concentration and molecular weight. In addition, rapid solvent extraction assists in reducing unwanted relaxation processes. Accordingly, increased control of the phase stability of P(VDF-ter-TrFE-ter-CFE) is gained. Moreover, pathways are opened to reliably identify processing routes for any given VDF-based polymer with critical information being obtained from thermal analysis and viscometry data only, enabling rapid feedback to materials design, including prediction of required molecular weights, without the need for use of complex characterization methodologies.
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Naser-et-al_ACS-Macro-Lett_2022-p410_Phase stabilisation -- Pouriamanesh et al -acs macro template- final.pdf (633.17 Ko)
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