Pouriamanesh Naser, Le Goupil Florian, Stingelin Natalie, Hadziioannou Georges
Université de Bordeaux, CNRS Bordeaux INP/ENSCBP, Laboratoire de Chimie des Polyméres Organiques, UMR 5629, Allée Geoffroy Saint-Hilaire, 33615, Pessac Cedex, France.
School of Materials Science and Engineering and School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, Georgia 30332, United States.
ACS Macro Lett. 2022 Apr 19;11(4):410-414. doi: 10.1021/acsmacrolett.2c00022. Epub 2022 Mar 8.
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 terpolymer P(VDF--TrFE--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, ε, is observed. Indeed, ε decreases little over time and saturates rapidly at 96-97% of its initial value. Mass transport thereby is limited by using highly entangled systems via the 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--TrFE--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 rheometry data only, enabling rapid feedback to material design, including the prediction of required molecular weights without the need for complex characterization methodologies.
基于偏二氟乙烯（VDF）的聚合物，如聚偏二氟乙烯（PVDF）及其共聚物，是众所周知的铁电体，在从能量存储到电热制冷的众多应用中都备受关注。然而，它们通常复杂的热相行为往往会导致低相稳定性，这可能会严重影响该材料家族的长期介电性能。在此，我们以三元共聚物P（VDF-TrFE-CFE）（摩尔比：64/29/7）为例证明，通过在固化过程和固态中限制质量传输/链段运动，观察到相对介电常数ε的“老化”大幅减小。实际上，ε随时间变化很小，并迅速饱和到其初始值的96 - 97%。通过选择合适的聚合物溶液浓度和分子量，利用高度缠结的体系来限制质量传输。此外，快速溶剂萃取有助于减少不必要的弛豫过程。因此，对P（VDF-TrFE-CFE）的相稳定性有了更好的控制。而且，为可靠地确定任何给定的基于VDF的聚合物的加工路线开辟了途径，仅从热分析和流变学数据中就能获得关键信息，从而能够快速反馈到材料设计中，包括预测所需的分子量，而无需复杂的表征方法。
