RESUMO
Electromagnetic interference (EMI) has been recognized as a new sort of pollution and can be considered as the direct interference of electromagnetic waves among electronic equipment that frequently affects their typical efficiency. As a result, shielding the electronics from this interfering radiation has been addressed as critical issue of great interest. In this study, different hybrid nanocomposites consisting of magnetite nanoparticles (Fe3O4) and reduced graphene oxide (rGO) as (conductive/magnetic) fillers, taking into account different rGO mass ratios, were synthesized and characterized by XRD, Raman spectroscopy, TEM and their magnetic properties were assessed via VSM. The acquired fillers were encapsulated in the polyurethane foam matrix with different loading percentages (wt%) to evaluate their role in EMI shielding. Moreover, their structure, morphology, and thermal stability were investigated by SEM, FTIR, and TGA, respectively. In addition, the impact of filler loading on their final mechanical properties was determined. The obtained results revealed that the Fe3O4@rGO composites displayed superparamagnetic behavior and acceptable electrical conductivity value. The performance assessment of the conducting Fe3O4@rGO/PU composite foams in EMI shielding efficiency (SE) was investigated at the X-band (8-12) GHz, and interestingly, an optimized value of SE -33 dBw was achieved with Fe3O4@rGO at a 80:20 wt% ratio and 35 wt% filler loading in the final effective PU matrix. Thus, this study sheds light on a novel optimization strategy for electromagnetic shielding, taking into account conducting new materials with variable filler loading, composition ratio, and mechanical properties in such a way as to open the door for achieving a remarkable SE.
RESUMO
Nanoparticle synthesis (~10-50 nm) of HCl-doped polyaniline elucidates the impact of limiting solvent (water) and oxidizing agent (ammonium peroxydisulfate) on morphology (XRD and TEM), chemical structure (FTIR), conductivity (two-point DC) and electromagnetic shielding effectiveness (SE) in microwave frequencies (i.e., X-band S-parameter measurements). Detailed comparison of these properties with respect to three distinct polymerization environments indicate that a solvent-free or limited solvent polymerization accomplished through a wet grinding solid-phase reaction produces superior conductivity (27 S/cm) with intermediate crystallinity (66%) for the highest EM shielding-an order of magnitude improvement over conventional polymerization with respect to EM power transmission reduction for all loadings per shielding area (0.04 to 0.17 g/cm(2)). By contrast, the classic oxidation of aniline in a well-dispersed aqueous reaction phase with an abundance of available oxidant in free solution yielded low conductivity (3.3 S/cm), crystallinity (54%), and SE, whereas similar solvent-rich reactions with limiting oxidizer produced similar conductivity (2.9 S/cm) and significantly lower SE with the highest crystallinity (72%). This work is the first to demonstrate that limiting solvent and oxidizer enhances electromagnetic interactions for shielding microwaves in polyaniline nanopowders. This appears connected to having the highest overall extent of oxidation achieved in the wet solid-phase reaction.
