Electrospinning Machine| Robust PI composites with high-connected AgNPs for multifunctional electromagnetic interference shielding in harsh environment

With the rapid development of modern 5G technology, electromagnetic radiation pollution has become a critical factor threatening the reliable operation of electronic devices and human health. Simultaneously, heat accumulation generated by high-power devices significantly reduces equipment performance and lifespan. Developing multifunctional materials with both efficient electromagnetic interference (EMI) shielding and thermal management capabilities has become a core requirement to ensure the stable operation of electronic systems in complex electromagnetic environments. Although durable EMI shielding materials have attracted much attention, the interfacial resistance between conductive fillers severely limits their performance breakthroughs.

Recently, the team of Prof. Liu Chuntai and Associate Prof. Su Fengmei from Zhengzhou University published a research paper titled "Robust PI composites with high-connected AgNPs for multifunctional electromagnetic interference shielding in harsh environments" in Composites Part B: Engineering. This work utilized an in-situ deposition-low-temperature sintering technique to construct a highly interconnected silver nanoparticle (AgNPs) network on the surface of electrospun polyimide (PI) nanofibers (Fig. 1), successfully preparing PI@Ag-S nanofiber composites with breakthrough achievements:
(i) The sintered interconnected silver network significantly increased conductivity from 49 S/cm to 154 S/cm;
(ii) Excellent EMI shielding effectiveness (86.7 dB) with SSE/t reaching 14,985 dB·cm²·g⁻¹;
(iii) Outstanding in-plane thermal conductivity (2.6011 W/(m·K)), an 8670% improvement over pure PI;
(iv) Superior electrothermal performance, achieving a steady-state temperature of 144°C at 1.5 V, enabling rapid defogging/de-icing.

Additionally, the composite, protected by an 8 μm PI coating, exhibits exceptional environmental adaptability, including resistance to extreme temperatures, strong acid/alkali corrosion, and flame retardancy, enabling efficient EMI shielding and thermal management in harsh environments.

Fig. 1: Preparation and properties of PI@Ag-S films.

After preparing PI@Ag films via electrospinning combined with chemical deposition (Fig. 1c), the material was subjected to low-temperature sintering at 200°C. As shown in Fig. 1d, AgNPs self-sintered through surface diffusion and grain boundary migration, forming cross-scale conductive pathways between adjacent fibers. This process increased conductivity by 214% (from 49 S/cm to 154 S/cm). Benefiting from the 3D interconnected silver network, the composite achieved an EMI shielding effectiveness (EMI SE) of 86.7 dB (Fig. 1e) while maintaining flexibility (bending radius <2 mm) and hydrophobicity (contact angle >135°), along with significantly enhanced electrothermal conversion performance (Fig. 1e).

Fig. 2: Morphology and structural characterization.

Material morphology and structure were characterized via SEM, XRD, and XPS. SEM confirmed that AgNPs were uniformly anchored on PI@PDA fibers after chemical reduction (Fig. 2i-j), with fiber diameter increasing to ~0.9 μm (Fig. 2c-d). High-resolution SEM revealed gaps between AgNPs in unsintered samples, whereas the sintered Ag layer became denser and smoother due to surface diffusion and grain boundary migration at 200°C, forming cross-fiber connections (Fig. 2e-f).

Fig. 3: EMI shielding performance and comparisons.

The interconnected AgNPs on PI nanofibers enhanced conductivity, improving EMI SE. As shown in Fig. 3c, PI@Ag-S (86.7 dB) far outperformed PI@Ag (47.9 dB) in EMI shielding, attributed to reduced interfacial resistance and lattice defects in AgNPs after sintering.

Fig. 4: Thermal conductivity.

As shown in Fig. 4, pure PI had an in-plane thermal conductivity (TC) of only 0.003 W/(m·K), which increased to 2.2804 W/(m·K) after silver coating and further to 2.6011 W/(m·K) post-sintering. This improvement stems from AgNPs' high intrinsic TC and enhanced connectivity, reducing interfacial thermal resistance and optimizing phonon transport.

Fig. 5: Electrothermal performance.

The conductive network also significantly improved Joule heating performance. As shown in Fig. 5a-d, PI@Ag-S achieved steady-state temperatures of 39°C, 81°C, and 144°C at 0.5 V, 1 V, and 1.5 V, respectively, maintaining uniform heating even when bent (Fig. 5e). Thus, PI@Ag-S films can serve as Joule heaters for rapid defogging/de-icing in extreme environments (Fig. 5f).

Fig. 6: Performance in extreme environments.

The PIAS composite, fabricated via hot pressing, PAA solution impregnation, and thermal imidization, exhibited a sandwich structure with a 41 μm PI@Ag layer and an 8 μm PI surface layer (Fig. 6b). It retained high EMI shielding performance after exposure to high/low temperatures, strong acids/alkalis, and ultrasonication, along with excellent mechanical strength and flame retardancy for harsh environments.

ln summary, combining electrospinning-chemical deposition-low-temperature sintering, we developed a flexible, lightweight PI@Ag-S composite film with breakthrough properties:EMI SE: 86.7 dB (X-band);In-plane TC: 2.60 W/(m·K);Joule heating: 144°C at 1.5 V (response time <15 s).The material also demonstrates exceptional environmental tolerance and flame retardancy, maintaining stability in extreme conditions.

Paper link: https://doi.org/10.1016/j.compositesb.2025.112735