Temperature-Dependent Rotational Dipole Mobility and Devitrification of the Rigid Amorphous Fraction in Unpoled and Poled Biaxially Oriented Poly(vinylidene fluoride)
Temperature-Dependent Rotational Dipole Mobility and Devitrification of the Rigid Amorphous Fraction in Unpoled and Poled Biaxially Oriented Poly(vinylidene fluoride)
复制标题
DOI：
10.1021/acs.macromol.2c01110
复制
发表时间：
2022-10
期刊：
影响因子：
5.5
通讯作者：
Guanchun Rui;E. Allahyarov;John J. Thomas;P. Taylor;Lei Zhu
中科院分区：
文献类型：
--
作者：
Guanchun Rui;E. Allahyarov;John J. Thomas;P. Taylor;Lei Zhu
除了从极性结晶相明显的铁电性质外，聚偏氟乙烯（PVDF）及其无规共聚物也表现出高介电常数，这是由于在非晶相中具有高度可移动的偶极子。在这项研究中，我们开发了一种新的理论方法来测定PVDF的偶极子浓度、偶极子矩、偶极子-偶极子相互作用和旋转偶极子迁移率。从熔融PVDF的介电常数出发，确定了Kirkwood-Fröhlichg-factor及其与温度的依赖关系，并将其作为模拟非极化和高度极化双轴取向PVDF （BOPVDF）的全局参数。从- 30℃到40℃，随着温度的升高，活性偶极子的浓度显著增加，表明刚性非晶部分（RAF）的反玻璃化。计算得到的极化BOPVDF的偶极矩和g因子均高于未极化BOPVDF，从而获得更高的介电常数和压电性能。此外，偶极-偶极相互作用在温度从- 30°C增加到40°C时显著增加，导致旋转偶极子迁移率增加4个数量级以上。这是在未极化和极化的BOPVDF中RAF脱玻璃化的直接证据。
In addition to the pronounced ferroelectric property from polar crystalline phases, poly(vinylidene fluoride) (PVDF) and its random copolymers also exhibit high dielectric permittivities as a result of highly mobile dipoles in the amorphous phase. In this study, we developed a new theoretical approach to determine the dipole concentration, dipole moment, dipole–dipole interaction, and rotational dipole mobility for PVDF by means of broadband dielectric spectroscopy. From the permittivity of molten PVDF, the Kirkwood–Fröhlichg-factor and its temperature dependence were determined and used as global parameters for the simulation of unpoled and highly poled biaxially oriented PVDF (BOPVDF). It was found that the concentration of active dipoles substantially increased as the temperature was increased from −30 to 40 °C, indicative of the devitrification of the rigid amorphous fraction (RAF). Both the calculated dipole moment and theg-factor of poled BOPVDF were higher than those of unpoled BOPVDF, resulting in a higher permittivity and piezoelectric performance. In addition, the dipole–dipole interaction was found to increase substantially upon increasing the temperature from −30 to 40 °C, leading to an increase of over 4 orders of magnitude in the rotational dipole mobility. This was direct evidence for the devitrification of the RAF in both unpoled and poled BOPVDF.