Department of Materials Engineering, Indian Institute of Science , Bangalore, India 560012.
ACS Appl Mater Interfaces. 2015 Nov 18;7(45):25448-63. doi: 10.1021/acsami.5b08333. Epub 2015 Nov 6.
Engineering blend structure with tailor-made distribution of nanoparticles is the prime requisite to obtain materials with extraordinary properties. Herein, a unique strategy of distributing nanoparticles in different phases of a blend structure has resulted in >99% blocking of incoming electromagnetic (EM) radiation. This is accomplished by designing a ternary polymer blend structure using polycarbonate (PC), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) to simultaneously improve the structural, electrical, and electromagnetic interference shielding (EMI). The blend structure was made conducting by preferentially localizing the multi-wall nanotubes (MWNTs) in the PVDF phase. By taking advantage of "π-π stacking" MWNTs was noncovalently modified with an imidazolium based ionic liquid (IL). Interestingly, the enhanced dispersion of IL-MWNTs in PVDF improved the electrical conductivity of the blends significantly. While one key requisite to attenuate EM radiation (i.e., electrical conductivity) was achieved using MWNTs, the magnetic properties of the blend structure was tuned by introducing barium ferrite (BaFe) nanoparticles, which can interact with the incoming EM radiation. By suitably modifying the surface of BaFe nanoparticles, we can tailor their localization under the macroscopic processing condition. The precise localization of BaFe nanoparticles in the PC phase, due to nucleophilic substitution reaction, and the MWNTs in the PVDF phase not only improved the conductivity but also facilitated in absorption of the incoming microwave radiation due to synergetic effect from MWNT and BaFe. The shielding effectiveness (SE) was measured in X and Ku band, and an enhanced SE of -37 dB was noted at 18 GHz frequency. PMMA, which acted as an interfacial modifier in PC/PVDF blends further, resulting in a significant enhancement in the mechanical properties besides retaining high SE. This study opens a new avenue in designing mechanically strong microwave absorbers with a suitable combination of materials.
工程共混结构与定制分布的纳米粒子是获得具有特殊性能材料的首要要求。在此，通过设计使用聚碳酸酯（PC）、聚偏二氟乙烯（PVDF）和聚甲基丙烯酸甲酯（PMMA）的三元聚合物共混结构，将纳米粒子分布在共混结构的不同相中，从而实现了对入射电磁（EM）辐射的>99%阻挡。这是通过设计使用聚碳酸酯（PC）、聚偏二氟乙烯（PVDF）和聚甲基丙烯酸甲酯（PMMA）的三元聚合物共混结构来实现的，以同时改善结构、电和电磁干扰屏蔽（EMI）。通过优先将多壁纳米管（MWNTs）定位在 PVDF 相中，使共混结构具有导电性。利用 MWNTs 的“π-π堆积”，MWNTs 被非共价地用咪唑鎓基离子液体（IL）修饰。有趣的是，IL-MWNTs 在 PVDF 中的增强分散显著提高了共混物的电导率。虽然使用 MWNTs 实现了衰减 EM 辐射（即电导率）的一个关键要求，但通过引入钡铁氧体（BaFe）纳米粒子来调整共混结构的磁性，这些纳米粒子可以与入射 EM 辐射相互作用。通过适当修饰 BaFe 纳米粒子的表面，可以根据宏观加工条件来调整其定位。由于亲核取代反应，BaFe 纳米粒子在 PC 相中以及 MWNTs 在 PVDF 相中精确定位，不仅提高了导电性，而且由于 MWNT 和 BaFe 的协同效应，促进了入射微波辐射的吸收。在 X 和 Ku 波段测量了屏蔽效能（SE），在 18GHz 频率下，注意到 SE 增强了-37dB。PMMA 作为 PC/PVDF 共混物中的界面改性剂，除了保持高 SE 外，还进一步提高了机械性能。这项研究为设计具有合适材料组合的机械强度高的微波吸收剂开辟了新途径。
