Preparation of Ag‐ <scp> CoFe ₂ O ₄ </scp> @ <scp>rGO</scp> Filler for Polar <scp>PVDF</scp> Polymer and Hexadecyltrimethoxysilane‐Modified Ag‐ <scp> CoFe ₂ O ₄ </scp> @ <scp>rGO</scp> Filler for Nonpolar <

ABSTRACT The CoFe 2 O 4 @reduced graphite oxide (rGO) was prepared by a one‐step solvothermal reaction, and then the Ag nanoparticles were deposited on the CoFe 2 O 4 @rGO by a green mild reduction reaction to form the novel Ag‐CoFe 2 O 4 @rGO filler, followed by the modification of Ag‐CoFe 2 O 4 @rGO using hexadecyltrimethoxysilane to form the novel H‐Ag‐CoFe 2 O 4 @rGO filler. The homogeneous distribution of the Ag‐CoFe 2 O 4 @rGO and H‐Ag‐CoFe 2 O 4 @rGO fillers in the polar PVDF plastic polymer and nonpolar SBS elastomer copolymer, respectively, to form the corresponding composites was proved by SEM. The polar crystal content of the PVDF matrix in the Ag‐CoFe 2 O 4 @rGO(10 wt.%)/PVDF composite was 36.13%, while the corresponding value for pure PVDF was 29.38%. The dielectric constant at 1000 Hz of Ag‐CoFe 2 O 4 @rGO(10 wt.%)/PVDF and H‐Ag‐CoFe 2 O 4 @rGO(10 wt.%)/SBS composites was 15.54 and 2.78, respectively, while the corresponding values for pure PVDF and pure SBS were 8.39 and 2.05, respectively. Additionally, although both pure PVDF and pure SBS were non‐magnetic, the magnetization values of Ag‐CoFe 2 O 4 @rGO(10 wt.%)/PVDF and H‐Ag‐CoFe 2 O 4 @rGO(10 wt.%)/SBS composites were 0.83 emu/g and 0.47 emu/g, respectively, at 50,000 Oe. The as‐prepared Ag‐CoFe 2 O 4 @rGO/PVDF and H‐Ag‐CoFe 2 O 4 @rGO/SBS composites should have the potential for different applications including dielectric capacitors, dielectric elastomers, sensors, EMI shielding, and so on.