Silver-Based Filler Silicone Rubber Composites for Electromagnetic Interference Shielding Applications

Electromagnetic interference (EMI) shielding materials are critical for reducing EMI pollution and enhancing information security. This study presents a systematic comparison of silver-plated copper (Cu@Ag; flake-like morphology; the average particle size D50 = 20.1 μm) and silver-plated aluminium (Al@Ag; spherical morphology; D50 = 47.5 μm) fillers with distinct morphologies incorporated into silicone rubber matrices via Rheomixer blending, open-mill compounding, and peroxide vulcanisation. This work aims to elucidate how filler morphology and multilayer sandwich architecture govern shielding efficiency and related material properties. The flake-like Cu@Ag fillers demonstrated superior low-loading performance. Due to their high aspect ratio and enhanced interfacial contact, Cu@Ag composites reached a critical loading for practical EMI shielding performance at 150 phr. In contrast, spherical Al@Ag fillers required a higher loading of 200 phr to achieve the same effect. Both composites achieved EMI shielding effectiveness exceeding 90 dB at 250 phr filler loading across the X-band frequency range (8.2-12.4 GHz). Innovatively, sandwich-structured composites were fabricated by combining Cu@Ag and Al@Ag layers through co-vulcanization, achieving approximately 110 dB shielding effectiveness, which is a ~33% improvement over single-layer composites at equivalent filler loading (200 phr). Analysis of the shielding mechanisms reveals that this enhancement results from multiple electromagnetic wave interactions, including increased reflection losses at morphologically distinct layer interfaces and enhanced absorption through conductivity gradients. This work demonstrates that a rational combination of flake-like and spherical fillers with contrasting morphologies and conductivity characteristics in multilayer architectures provides a powerful strategy for developing high-performance flexible EMI shielding materials.