Negative permittivity is a key characteristic of the distinctive metamaterials, a novel class of artificial materials with particular electromagnetic properties. Negative permittivity has been realized in metallic structures with special designs, but rarely achieved in polymer nanocomposites. Our recent studies discover that negative permittivity can be attained from randomly distributed carbon nanofiber (CNF) filled poly(vinylidene fluoride) (PVDF) composites over a wide frequency range, and the negative permittivity values are strongly influenced by CNF and PVDF crystalline structures. The effects of CNF on the crystallization of PVDF, and the resultant negative dielectric permittivity of CNF/PVDF composites influenced by crystallization of PVDF and CNF, are investigated. It is revealed that the introduction of CNF not only affects the dielectric permittivity directly, but also causes indirect effects to the dielectric permittivity through influencing the crystallization of PVDF. In particular, due to addition of more CNF, a α‐ to β‐phase transformation in PVDF is found to affect permittivity of the nanocomposites. Furthermore, the permittivity of CNF/PVDF composites are increased considerably (“more negative”) with more CNF, and is affected noticeably by crystalline structures of PVDF. The lowest negative permittivity achieved is −2,500 for the nanocomposite with 5 wt% CNF at 5 kHz.

中文翻译：

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碳纳米纤维和聚合物结晶引起的PVDF纳米复合材料的负介电常数

负介电常数是独特的超材料的关键特征，超材料是具有特殊电磁特性的新型人造材料。负介电常数已在具有特殊设计的金属结构中实现，但很少在聚合物纳米复合材料中实现。我们最近的研究发现，从很宽的频率范围内，随机分布的碳纳米纤维（CNF）填充的聚偏二氟乙烯（PVDF）复合材料可以获得负介电常数，并且负介电常数值受CNF和PVDF晶体结构的强烈影响。研究了CNF对PVDF结晶的影响，以及CNPV / PVDF复合材料在PVDF和CNF结晶作用下产生的负介电常数。揭示了CNF的引入不仅直接影响介电常数，而且通过影响PVDF的结晶而间接影响介电常数。特别是，由于添加了更多的CNF，发现PVDF中的α相到β相转变会影响纳米复合材料的介电常数。此外，CNF / PVDF复合材料的介电常数随着CNF的增加而显着增加（“更负”），并且明显受到PVDF晶体结构的影响。对于具有5wt％CNF的纳米复合材料，在5kHz下，获得的最低的负介电常数是-2,500。发现PVDF中的α相到β相转变会影响纳米复合材料的介电常数。此外，CNF / PVDF复合材料的介电常数随着CNF的增加而显着增加（“更负”），并且明显受到PVDF晶体结构的影响。对于具有5wt％CNF的纳米复合材料，在5kHz下，获得的最低的负介电常数是-2,500。发现PVDF中的α相到β相转变会影响纳米复合材料的介电常数。此外，CNF / PVDF复合材料的介电常数随着CNF的增加而显着增加（“更负”），并且明显受到PVDF晶体结构的影响。对于具有5wt％CNF在5kHz的纳米复合材料，所获得的最低的负介电常数是-2,500。