This study sheds light on the effect of nitrogen (N) doping of carbon nanotubes (CNTs) on medium-amplitude oscillatory shear (MAOS) response of CNT/polyvinylidene fluoride (PVDF) nanocomposites within a rheologically percolated concentration regime. Custom-synthesized CNTs without and with nitrogen heteroatom (at a nitrogen atomic percent of 3.85 at. %) were incorporated into a PVDF matrix using a miniature melt-mixer at different concentrations. In both cases, as confirmed by TEM investigations, a nanoscopic state of dispersion in the PVDF matrix was achievable using the applied melt mixing procedure. Our results indicated that N-doped nanocomposites, well below their electrical percolation, form a hybrid, load-bearing network structure where network interconnectivity is driven by N-doped CNT domains and near-surface regions of the PVDF phase. This hybrid network formation behavior combined with N-doped CNTs inferior aspect ratio and their higher susceptibility to breakage and length loss during the melt mixing process have led to delayed electrical percolation. In contrast, localized clustering and contact aggregation in a submicrometer scale was the dominant mode of network formation in the undoped CNT/PVDF nanocomposites. These microstructural inferences were further validated in the frame of molecular simulations and optical microscopy investigations.

中文翻译：

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氮掺杂对纳米管/聚偏二氟乙烯纳米复合材料中振幅振荡剪切 (MAOS) 响应的影响：分子模拟、流变学和宽带电导率

这项研究揭示了碳纳米管 (CNT) 的氮 (N) 掺杂对 CNT/聚偏二氟乙烯 (PVDF) 纳米复合材料在流变渗透浓度范围内的中振幅振荡剪切 (MAOS) 响应的影响。使用微型熔体混合器以不同浓度将定制合成的 CNT 不含和含氮杂原子（氮原子百分比为 3.85 原子百分比）并入 PVDF 基质中。在这两种情况下，正如 TEM 研究证实的那样，使用应用的熔体混合程序可以实现 PVDF 基质中的纳米级分散状态。我们的结果表明，N 掺杂纳米复合材料，远低于它们的电渗透，形成混合的、承载网络结构，其中网络互连由 N 掺杂的 CNT 域和 PVDF 相的近表面区域驱动。这种混合网络的形成行为与 N 掺杂的 CNT 较低的纵横比以及它们在熔体混合过程中对断裂和长度损失的更高敏感性相结合，导致电渗透延迟。相比之下，亚微米尺度的局部聚集和接触聚集是未掺杂的 CNT/PVDF 纳米复合材料中网络形成的主要模式。这些微观结构推论在分子模拟和光学显微镜研究的框架中得到了进一步验证。亚微米尺度的局部聚集和接触聚集是未掺杂的 CNT/PVDF 纳米复合材料中网络形成的主要模式。这些微观结构推论在分子模拟和光学显微镜研究的框架中得到了进一步验证。亚微米尺度的局部聚集和接触聚集是未掺杂的 CNT/PVDF 纳米复合材料中网络形成的主要模式。这些微观结构推论在分子模拟和光学显微镜研究的框架中得到了进一步验证。