聚偏二氟乙烯 (PVDF) 以其压电特性而闻名。这种材料具有不同的晶相,α (α)、β (β) 和 γ (γ),其中 β 相尤其与 PVDF 的压电行为有关。虽然 PVDF 中从 α 相到 β 相的转变有据可查并得到广泛研究,但从 γ 相到 β 相的转变尚未得到充分探索。然而,当 PVDF 通过某些基于溶液的方法生产时,它可以采用其γ形式,它不像 β 相那样压电。因此,本研究旨在通过研究通过基于溶液的技术获得的 PVDF 纳米复合材料薄膜从γ相到β相的转变来弥合这一差距。我们的 PVDF 纳米复合材料是通过溶剂蒸发辅助 3D 打印 PVDF 纳米复合材料与钛酸钡纳米颗粒 (BTO) 制成的。为了实现 γ 相到 β 相转变,我们首先强调退火在 PVDF 样品成功极化中的重要性。然后,我们使用傅里叶变换红外光谱 (FTIR)、X 射线衍射 (XRD) 和差示扫描量热法 (DSC) 对 PVDF-BTO 的α、β和γ晶体相进行深入分析。我们观察到,退火后但在极化之前,PVDF-BTO 纳米复合材料含有 76% 的 β + γ 相,其中大部分是 γ 相。对这些样品进行极化,β + γ 相的组合达到 93%,出现 β 相绝对分数的 40%。然后,我们证明了纳米复合材料中β相的分数——如 PVDF 的 FTIR 光谱中的 1275 cm-1 峰所示——在薄膜的表面积上并不均匀。 此外,绝对β相含量的值还取决于极化场的方向。我们的研究表明,在考虑 PVDF 的压电行为时,了解这些细微差别至关重要,本文提供了有关如何解决这些细微差别的重要见解。总体而言,本研究为增强基于 PVDF 的纳米复合材料的压电性传感应用提供了分步指南。
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Unleashing the piezoelectric potential of PVDF: a study on phase transformation from gamma (γ) to beta (β) phase through thermal contact poling
Polyvinylidene fluoride (PVDF) is known for its piezoelectric properties. This material has different crystalline phases, alpha (α), beta (β) and gamma (γ), where the β-phase, in particular, is related to the piezoelectric behavior of PVDF. While the transformation from the α-phase to β-phase in PVDF is well-documented and widely studied, the transformation from γ- to β-phase has not yet been fully explored. However, when PVDF is produced by certain solution-based methods it can adopt its γ-form, which is not as piezoelectric as the β-phase. Hence, this study aims to bridge this gap by investigating the transformation from γ- to β-phase in PVDF nanocomposites films obtained from solution-based techniques. Our PVDF nanocomposite is made by solvent evaporation-assisted 3D printing of PVDF's nanocomposite with barium-titanate nanoparticles (BTO). To achieve the γ- to β-phase transformation, we first highlight the importance of annealing in the successful poling of PVDF samples. We then perform an in-depth analysis of the α-, β- and γ-crystallographic phases of PVDF-BTO using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). We observed that after annealing but before poling, the PVDF-BTO nanocomposite contains 76% of β + γ phases, the majority of which is the γ-phase. Poling of these samples resulted in the combination of the β + γ phases reaching 93% with the appearance of 40% of absolute fraction of the β-phase. We then demonstrated that the fraction of β-phase in the nanocomposite – as indicated by the 1275 cm−1 peak in PVDF's FTIR spectra – is not uniform on the surface area of the film. Additionally, the value of the absolute β-phase content also depends on the poling field's direction. Our work reveals that while considering PVDF's piezoelectric behavior, it is critical to be aware of these nuances and this article offers essential insights on how to address them. Overall, this study provides a step-by-step guideline to enhance the piezoelectricity of PVDF-based nanocomposites for sensing applications.