Asymmetric Aerodynamic Shear via L-Shaped Needle Directs Cobalt-Domain Assembly in Solution-Blown Carbon Nanofibers for Broadband Microwave Absorption

The spatial distribution of magnetic nanofillers within fibrous carbon scaffolds determines both impedance matching and broadband attenuation, yet the aerodynamic forces governing filler rearrangement during spinning remain unexploited as a design variable. We demonstrate that an L-shaped precursor needle within a solution blow spinning nozzle generates asymmetric aerodynamic shear. This shear converts the near-nozzle gas flow from a symmetric annular jet into a localized asymmetric forcing field. Large-eddy simulations reveal gas-phase shear rates above 3.0 × 10⁵ s⁻¹ and coherent vortical structures absent in conventional nozzles. The near-nozzle extensional stress exceeds the van der Waals cohesion of Co@BCN bundles, consistent with the disaggregated cobalt domains observed after carbonization. Post-carbonization electron microscopy and elemental mapping reveal discrete cobalt domains within the carbon nanofiber matrix, a configuration that enhances interfacial polarization while suppressing percolative conductivity. At 10 wt.% filler loading in the paraffin matrix, the optimized Co@BCN-CF-2 achieves a minimum reflection loss of −69.4 dB at 8.08 GHz (3.4 mm). The effective absorption bandwidth reaches 5.2 GHz (2.2 mm), and the simulated radar cross-section reduction attains 20.98 dB. These findings establish near-nozzle aerodynamic forcing as a demonstrated, tunable processing variable for filler-domain assembly in the present Co@BCN/PAN SBS nanofiber system.