Room-Temperature Ferromagnetic Sr3YCo4O10+δ and Carbon Black-Reinforced PolyvinylidenefluorideComposites toward High-Performance Electromagnetic Interference Shielding

摘要

In this study, we fabricated composites of conducting carbon black (CB), room-temperature ferromagnetic Sr3YCo4O10+δ (SYCO) and polyvinylidenefluoride (PVDF) by the solution mixing and coagulation method for the first time. During the nucleation process of PVDF, the presence of SYCO and CB individually facilitates the crystallization of polar β and semipolar γ phases along with the nonpolar α phase in PVDF. The dc electrical conductivity of PVDF raised from 1.54 × 10^–8 to 9.97 S/m with the addition of 30 wt % of CB, and it is nearly constant with respect to the SYCO content. The PVDF/CB/SYCO composites (PCS) possess high permittivity and its variation is in accordance with the content of polar phases in PVDF. Moreover, the complex permittivity and permeability spectra from 10 MHz to 1 GHz indicate that the dielectric loss dictates over magnetic loss in these composites. The electromagnetic interference shielding effectiveness (EMI SE) of PCS composites is higher than that of PVDF/CB and PVDF/SYCO composites in the 8.2–18 GHz region. Addition of SYCO in the PVDF/CB matrix enhances shielding by dominated absorption with minimal reflection. The analysis of theshielding mechanism suggests that in addition to conducting and magneticlosses due to CB and SYCO, respectively, the synergy among CB, SYCO,and PVDF promotes shielding by matching the input impedance to thatof free space, enhancing multiple internal reflections from SYCO andsubsequent absorption by CB, eddy current losses, dielectric dampinglosses, interfacial polarization losses, and so forth. These differentmechanisms result in an enhanced EMI SE of 50.2 dB for the PCS-40composite for a thickness of 2.5 mm.