Can Relaxor Ferroelectric Behavior Be Realized for Poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF-CTFE)] Random Copolymers by Inclusion of CTFE Units in PVDF Crystals?
Can Relaxor Ferroelectric Behavior Be Realized for Poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF-CTFE)] Random Copolymers by Inclusion of CTFE Units in PVDF Crystals?
复制标题
通过在 PVDF 晶体中包含 CTFE 单元，能否实现聚（偏二氟乙烯-三氟氯乙烯）[P(VDF-CTFE)] 无规共聚物的弛豫铁电行为？
DOI：
10.1021/acs.macromol.8b01155
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发表时间：
2018-07-24
期刊：
影响因子：
5.5
通讯作者：
Zhu, Lei
中科院分区：
文献类型：
--
作者：
Huang, Yanfei;Xu, Jia-Zhuang;Zhu, Lei
弛豫铁电（RFE）聚合物由于其高介电常数和低磁滞损耗而在电致伸缩致动、机电传感器、电能存储和电热冷却等各种电气应用中具有吸引力。目前最先进的RFE聚合物包括基于聚（偏二氟乙烯-共-三氟乙烯）[P（VDF-TrFE）]的无规共聚物和三元共聚物。然而，由于TrFE的安全性问题而导致的高成本使得它们的短期商业化变得困难。非常希望探索不含TrFE的PVDF共聚物的机会[例如，P（VDF-CTFE）; CTFE是三氟氯乙烯]以通过在PVDF晶体中包含CTFE来实现RFE行为（即，同构）。在这项工作中，采用两种策略，包括在PVDF晶体中的CTFE。首先，高压结晶被用来获得扩展链晶体通过伪六方顺电相。结构分析表明，CTFE单元在很大程度上被排除在PVDF的γ晶胞和铁电畴之外，但位于延伸链层内的扭结。结果，由于大的铁电伽马畴，没有观察到RFE行为。第二种策略利用在低温（-20至0摄氏度）下的机械拉伸以获得取向的小β微晶（约100微米）。5-7 nm）。结构分析表明，CTFE单元被排除在β晶胞之外，位于晶体-非晶界面。尽管由于小的微晶尺寸，磁滞回线变得有些纤细，但仍然没有实现具有纤细磁滞回线的RFE行为。该研究表明，CTFE单元太大而不能包括在紧密堆积的PVDF晶胞中，无论是α、γ还是β相。在未来，希望探索具有较小共聚单体（例如1-氯-1-氟乙烯）的其它PVDF共聚物。
Relaxor ferroelectric (RFE) polymers are attractive for various electrical applications such as electrostrictive actuation, electromechanical sensors, electric energy storage, and electrocaloric cooling because of their high dielectric constants and low hysteresis loss. Current state-of-the-art RFE polymers include poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]-based random copolymers and terpolymers. However, the high costs due to a safety concern of TrFE make their near term commercialization difficult. It is highly desirable to explore the opportunity of TrFE-free PVDF copolymers [e.g., P(VDF-CTFE); CTFE is chlorotrifluoroethylene] to achieve the RFE behavior by inclusion of CTFE in PVDF crystals (i.e., isomorphism). In this work, two strategies were employed to include CTFE in PVDF crystals. First, high-pressure crystallization was used to obtain extended-chain crystals via the pseudohexagonal paraelectric phase. Structural analyses indicated that CTFE units were largely excluded from the gamma unit cells and ferroelectric domains of PVDF but located as kinks inside the extended chain lamellae. As a result, no RFE behavior was observed because of large ferroelectric gamma domains. The second strategy utilized mechanical stretching at low temperatures (-20 to 0 degrees C) to obtain oriented small beta crystallites (ca. 5-7 nm). Structural analyses indicated that CTFE units were excluded from the beta unit cells, locating at the crystal-amorphous interfaces. Although the hysteresis loops became somewhat slimmer as a result of small crystallite sizes, the RFE behavior with slim hysteresis loops was still not achieved. This study demonstrated that CTFE units were too large to be included in the tightly packed PVDF unit cells, whether the alpha, gamma, or beta phase. In the future, it is desirable to explore other PVDF copolymers with a smaller comonomer such as 1-chloro-1-fluoroethylene.