School of Materials Science and Engineering, Beihang University , Beijing 100191, China.
Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology , Beijing 100191, China.
ACS Appl Mater Interfaces. 2017 Dec 27;9(51):44839-44846. doi: 10.1021/acsami.7b14751. Epub 2017 Dec 12.
Design of composites with ordered fillers arrangement results in anisotropic performances with greatly enhanced properties along a specific direction, which is a powerful tool to optimize physical properties of composites. Well-aligned core-shell SiC@SiO whiskers in poly(vinylidene fluoride) (PVDF) matrix has been achieved via a modified spinning approach. Because of the high aspect ratio of SiC whiskers, strong anisotropy and significant enhancement in dielectric constant were observed with permittivity 854 along the parallel direction versus 71 along the perpendicular direction at 20 vol % SiC@SiO loading, while little increase in dielectric loss was found due to the highly insulating SiO shell. The anisotropic dielectric behavior of the composite is perfectly understood macroscopically to have originated from anisotropic intensity of interfacial polarization based on an equivalent circuit model of two parallel RC circuits connected in series. Furthermore, finite element simulations on the three-dimensional distribution of local electric field, polarization, and leakage current density in oriented SiC@SiO/PVDF composites under different applied electrical field directions unambiguously revealed that aligned core-shell SiC@SiO whiskers with a high aspect ratio significantly improved dielectric performances. Importantly, the thermal conductivity of the composite was synchronously enhanced over 7 times as compared to that of PVDF matrix along the parallel direction at 20 vol % SiC@SiO whiskers loading. This study highlights an effective strategy to achieve excellent comprehensive properties for high-k dielectrics.
具有有序填充排列的复合材料设计可导致各向异性性能，沿特定方向具有大大增强的性能，这是优化复合材料物理性能的有力工具。通过改进的纺丝方法，在聚偏二氟乙烯（PVDF）基体中实现了具有良好取向的核壳 SiC@SiO 晶须。由于 SiC 晶须的高纵横比，在 20vol% SiC@SiO 负载下，观察到与垂直方向（71）相比，平行方向（854）的介电常数具有很强的各向异性和显著增强，而由于高度绝缘的 SiO 壳，介电损耗几乎没有增加。基于两个串联 RC 电路的等效电路模型，宏观上完美地理解了复合材料的各向异性介电行为，该模型源自界面极化强度的各向异性。此外，在不同外加电场方向下，对取向 SiC@SiO/PVDF 复合材料中局部电场、极化和漏电流密度的三维分布进行有限元模拟，明确揭示了具有高纵横比的定向核壳 SiC@SiO 晶须可显著改善介电性能。重要的是，与 PVDF 基体相比，在 20vol% SiC@SiO 晶须负载下，复合材料的热导率沿平行方向同步提高了 7 倍以上。该研究强调了一种实现高介电常数复合材料优异综合性能的有效策略。
