In this study, we report the dependence of the nanoparticle dispersion on the zero-conversion initiator efficiency in the nanocomposites formed by poly(N-vinyl carbazole) (PNVK) and acrylic acid-modified iron oxide (AA-Fe₃O₄) nanoparticles via free radical solution polymerization of the precursor solution, that is, a thorough mixture of 28.5 wt% AA-Fe₃O₄ nanoparticles and the N-vinyl carbazole (NVK) monomer with the solvent dimethylformamide and azobisisobutyronitrile as an initiator. Here three different types of the dispersion state of AA-Fe₃O₄ nanoparticles in the PNVK matrix have been distinguished by a combined approach of transmission electron microscopy and small-angle X-ray scattering coupled with real-space models of the nanoparticle assemblies. When the polymerization proceeded with a higher zero-conversion initiator efficiency (f°) by pre-polymerization at 115 °C, the generation of a large amount of free radicals could efficiently induce the dominant surface-initiated polymerization of the NVK monomer with the vinyl groups of tethered acrylic acids; in this case, the constitution of “shorter multiple grafted PNVK chains” threaded AA-Fe₃O₄ nanoparticles to form particle branches and the branches were joined together from branching points along each branch, thereby forming the network structure. However, once the polymerization was conducted at a lower f° by pre-polymerization at 75 °C, a significant reduction in the generation of free radicals likely greatly reduced the efficiency in the occurrence of surface-initiated polymerization at particle surfaces; nevertheless, the self-polymerization of the NVK monomer could still take place to induce a local demixing between the polymerizing longer PNVK chains and AA-Fe₃O₄ nanoparticles via the attractive depletion mechanism, thus locally leading to the formation of small aggregates. While if the f° was controlled to be intermediate by polymerization at 100 °C, an optimal balance between the rates of the surface-initiated polymerization and the self-polymerization induced a collective construction built from the network and aggregate structures, exhibiting the structural characteristics of large aggregates. Furthermore, the magnetic coercivity of PNVK/AA-Fe₃O₄ nanocomposites was found to depend on the dispersion state of the AA-Fe₃O₄ nanoparticles, presenting a tendency towards enhanced coercivity as the dispersion state changed from large aggregates to small aggregates to network structure.

中文翻译：

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聚（N-乙烯基咔唑）/ Fe3O4纳米复合材料的层级结构及相关的矫顽力

在这项研究中，我们报告了纳米颗粒分散体对聚（N-乙烯基咔唑）（PNVK）和丙烯酸改性的氧化铁（AA-Fe ₃ O ₄）纳米颗粒形成的纳米复合材料中零转化引发剂效率的依赖性。通过前体溶液的自由基溶液聚合，即28.5 wt％的Aa -Fe ₃ O ₄纳米颗粒和N-乙烯基咔唑（NVK）单体与溶剂二甲基甲酰胺和偶氮二异丁腈的完全混合物作为引发剂。在这里，AA-Fe ₃ O _4的三种不同分散状态PNVK基质中的纳米颗粒通过透射电子显微镜和小角度X射线散射的结合方法与纳米颗粒组件的真实空间模型相结合而得到了区别。通过在115°C下进行预聚合使聚合反应以更高的零转化引发剂效率（f °）进行时，大量自由基的产生可以有效地诱导NVK单体与乙烯基的主要表面引发聚合反应束缚丙烯酸组；在这种情况下，“短接枝多个PNVK链”的AA-Fe ₃ O ₄螺纹构成纳米粒子形成粒子分支，并且分支沿着每个分支从分支点连接在一起，从而形成网络结构。然而，一旦通过在75℃下的预聚合在较低的f °下进行聚合，自由基的显着减少可能会大大降低颗粒表面发生表面引发聚合的效率。尽管如此，NVK单体的自聚合仍然可以通过引诱的耗尽机制在聚合的较长PNVK链和AA-Fe ₃ O ₄纳米粒子之间引起局部分解，从而局部导致形成小的聚集体。而如果˚F通过在100°C下进行聚合，可将°控制在中间，在表面引发的聚合速率和自聚合速率之间的最佳平衡导致了由网络和聚集体结构构成的集体构造，展现出大聚集体的结构特征。此外，发现PNVK / AA-Fe ₃ O ₄纳米复合材料的磁矫顽力取决于AA-Fe ₃ O ₄纳米颗粒的分散状态，随着分散状态从大聚集体变为小聚集体，呈现出矫顽力增强的趋势。网络结构。