A room-temperature self-healing and mechanically robust siloxane elastomer via synergistic complexation and cation–π interactions for high-performance electromagnetic interference shielding

Abstract

The rapid development of flexible electronic devices and the growing concern over electromagnetic radiation pollution have created an urgent need for electromagnetic interference (EMI) shielding materials with both excellent mechanical performance and room-temperature self-healing capability. However, it is still a big challenge to meet this requirement. In this work, a room-temperature self-healing and mechanically robust supramolecular elastomer is designed by incorporating an electron-rich indole derivative and Fe³⁺ into a siloxane polymer via synergistic short-range complexation interactions between Fe³⁺ and the indole derivative and long-range cation–π interactions between Fe³⁺ and the indole derivative as cross-linking points. The resulting siloxane elastomer exhibits excellent mechanical properties (tensile strength of 2.86 MPa and elongation at break of 487%), strong adhesion (923 kPa), and remarkable self-healing efficiency (99%). Leveraging its adhesive property, the siloxane elastomer is integrated with silver nanowires (Ag NWs) to fabricate a composite film. The composite film demonstrates excellent self-healing and superior EMI shielding effectiveness of up to 70.83 dB. This work presents a convenient and rapid strategy for developing multifunctional materials for next-generation flexible electronics.

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Ying Huang

Ying Huang received her Ph.D. degree from the School of Materials Science and Engineering, Nanyang Technological University, in 2018. Currently, she is an associate professor at Southwest University of Science and Technology. Her research interests focus on the design, synthesis and application of functional composite materials, with an emphasis on enhancing their self-healing and recyclable capabilities through dynamic bonds.

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1. Introduction

In recent years, the trend toward miniaturization and integration in flexible electronic devices has opened up exciting possibilities in applications such as wearable sensors and electronic skin.^1–5 However, these advances are accompanied by increasing challenges, including electromagnetic radiation pollution and interference, which pose risks to human health and impair the performance of sensitive electronic components.^6–12 Extensive research efforts have been devoted to the development of flexible electromagnetic interference (EMI) shielding materials to solve this problem. However, insufficient mechanical properties often limit the practical application of flexible electromagnetic interference materials. Moreover, they are inherently vulnerable to mechanical damage during use, leading to degradation in mechanical integrity and EMI shielding performance.^13,14 Therefore, the self-healing capability of flexible materials is essential for ensuring durability and reliability. This highlights an urgent need for flexible electronic materials that combine mechanical robustness, self-healing ability, and excellent electromagnetic interference (EMI) shielding performance.¹⁵

Flexible and self-healing conductive elastomers represent a promising class of materials for EMI shielding, offering enhanced mechanical reliability, durability, and service life. Among them, siloxane elastomers are considered as ideal matrices for developing self-healing EMI shielding materials due to their favorable properties such as water resistance, chemical resistance, excellent flexibility and biocompatibility.^16–22 However, pure siloxane elastomers lack intrinsic EMI shielding functionality. Incorporating conductive fillers (e.g., graphene,²³ MXene,²⁴ and silver nanowires (Ag NWs)²⁵) into siloxane elastomers is an effective strategy to impart EMI shielding performance. Ag NWs, in particular, offer high conductivity and flexibility, making them widely used in conductive siloxane elastomers. High Ag NW loading is often required to achieve effective EMI shielding performance, but excessive filler content restricts polymer chain mobility and promotes filler aggregation within the matrix, impairing self-healing efficiency and degrading mechanical properties. Many efforts have been made to construct conductive elastomers by coating self-healing siloxane substrates with conductive Ag NW layers. This approach leverages the substrate's intrinsic healing capability to restore conductivity via reconnection of damaged filler networks. For instance, Bai et al.²⁵ introduced oxime–urethane bonds into polydimethylsiloxane (PDMS) to fabricate an elastomeric adhesive (MFEA) with a self-healing efficiency of 91% at 90 °C, and combined it with an adhered Ag NW film to obtain good EMI shielding performance. Sun et al.²⁶ fabricated a tear-resistant and colourless EMI shielding elastomer by embedding Ag NWs within a highly dynamic hydrogen-bonded network, exhibiting high transparency (77.5%), low stiffness (0.1 MPa), satisfactory EMI shielding performance (43.1 dB), and autonomous self-healing performance. Despite progress, some challenges still remain including weak interfacial adhesion between inorganic conductive layers and organic elastomer substrates, limited room temperature self-healing capability and insufficient mechanical properties.²⁷ Therefore, it is highly desirable to develop siloxane elastomers that simultaneously exhibit strong mechanical properties, fast room-temperature self-healing capacity, excellent self-adhesion and outstanding EMI shielding performance through rational structural design.

Current strategies for endowing siloxane elastomers with self-healing properties often rely on reversible dynamic bonds,²⁸ including hydrogen bonds,²⁹ coordination bonds,³⁰ dynamic imines,³¹ Diels–Alder adducts,³² and disulfide bonds.³³ However, many still require long healing times, elevated temperatures, or additional stimuli, which limit practical use. To improve the self-adhesion of siloxane elastomers, biomimetic strategies including gecko feet³⁴ and octopus suckers,³⁵ have been employed, although they often depend on complex lithography. Alternatively, reducing cross-linking density can produce adhesives but typically sacrifices mechanical strength. These limitations have prompted efforts to develop siloxane elastomers that combine high mechanical strength, self-healing ability, and self-adhesive properties. For example, Tang et al.³⁶ reported a siloxane elastomer with a tensile strength of 0.43 MPa and ultrafast self-healing (100% efficiency within 30 s at room temperature). Han et al.³⁷ designed polydimethylsiloxane elastomers with both hydrogen bonding and metal coordination to achieve high toughness and adhesive strength. Other approaches have also advanced the development of siloxane elastomers.^38–43 Nevertheless, most of these elastomers suffer from at least one drawback: low mechanical strength, slow or incomplete healing, reliance on non-ambient conditions, or insufficient adhesion. Cation–π interactions, defined as electrostatic attractions between cations and π-electron systems, are characterized by a large binding area, tunable interaction distance, and dynamic reversibility, making them ideal for energy dissipation and mechanical reinforcement.^44–48 Therefore, the integration of cation–π interactions into siloxane elastomers may be a promising strategy to achieve self-healing, self-adhesion, and robust mechanical performance; however currently, there is limited research in this area.

Herein, we design a siloxane elastomer (INPDMS–Fe-x) by incorporating Fe³⁺ ions and 2-phenyl-1H-indol-3-amine (IN) into a PDMS matrix, forming dynamic cross-linked networks via synergistic complexation interactions between Fe³⁺ and the indole derivative and cation–π interactions between Fe³⁺ and the indole derivative. The Fe³⁺–π interactions provide long-range and reversible bonding, enhancing energy dissipation, elasticity, and self-healing performance. The Fe³⁺–indole derivative complex serves as a short-range interaction that anchors Fe³⁺, facilitating the formation of dynamic cation–π interactions with nearby indole derivatives (Fig. 1). As a result, the optimized INPDMS–Fe-0.8 elastomer exhibits an ideal balance of mechanical performance and self-healing ability. Notably, the as-prepared siloxane elastomer exhibits good adhesion to diverse substrates through synergistic interactions including metal coordination bonds, hydrogen bonds, cation–π interactions, π–π interactions and hydrophobic interactions. Owing to its excellent self-adhesive properties, the as-prepared siloxane elastomer can bond with Ag NW films under ambient conditions to form composite materials with high EMI shielding performance. This multifunctional elastomer material offers a convenient and scalable solution for next-generation flexible electronic devices.

Fig. 1 Molecular structure and preparation strategy of INPDMS–Fe-x.

2. Experimental

2.1 Materials

2-Phenylindole (99%) and sodium dithionite (Na₂S₂O₄, 90%) were purchased from Macklin (Shanghai, China). Iron(III) chloride (FeCl₃), acetic acid (CH₃COOH), sodium nitrite (NaNO₂), sodium hydroxide (NaOH), and tetrahydrofuran (THF) were obtained from Chengdu Chron Chemicals Co., Ltd (Chengdu China). Poly(dimethylsiloxane)diglycidyl ether (PDMS-GE, M_n ≈ 800 g mol⁻¹) was purchased from Sigma-Aldrich. Super-long silver nanowires (Ag NWs-L50; diameter: 50 nm; length: 100 μm) were supplied by XFNANO Materials Tech Co., Ltd (Nanjing, China). All other reagents were of analytical grade and used as received without further purification unless otherwise specified.

2.2 Preparation of INPDMS elastomer

2-Phenyl-1H-indol-3-amine (IN) was synthesized according to previously reported procedures (Fig. S1†).⁴⁹ The linear siloxane elastomer (INPDMS) was prepared following the method described in the literature.⁵⁰ Specifically, PDMS-GE and IN were mixed and stirred at 120 °C to form a homogeneous solution. The mixture was then poured into a preheated polytetrafluoroethylene (PTFE) mold. Degassing was conducted under vacuum at 80 °C for 30 minutes. The mixture was subsequently cured in an oven at 150 °C for 2 hours, followed by an additional 2 hours at 170 °C. The mold was then allowed to cool naturally to room temperature.

2.3 Preparation of INPDMS–Fe-x elastomers

1 g of INPDMS was dissolved in 10 mL of a THF solution containing FeCl₃ and stirred for 12 hours. The solvent was gradually removed by heating the mixture to 60 °C while stirring until a viscous solution was formed. This viscous solution was poured into a PTFE mold and left to dry at room temperature for 2 hours, followed by vacuum drying at 60 °C for 24 hours to remove residual solvent. The resulting elastomer was obtained by demolding. The as-prepared elastomer was denoted as INPDMS–Fe-x, where x represents the molar amount of Fe³⁺ (x = 0.2, 0.4, 0.6, 0.8, 1.0). The specific formulations are summarized in Table S1.†

2.4 Preparation of composite films

The composite films were fabricated through a vacuum filtration and transfer method by combining INPDMS–Fe-0.8 with Ag NWs. First, Ag NW suspensions were prepared by dispersing a certain amount (2, 4, 6, 8 and 10 mg) of Ag NWs in 150 mL deionized water, respectively, followed by vacuum filtration to form continuous Ag NW networks on the surface of microporous filter membranes. Subsequently, the Ag NW-coated microporous filter membranes were transferred onto INPDMS–Fe-0.8 substrates and then heated to 60 °C to ensure robust interfacial adhesion. After cooling to room temperature, the microporous filter membrane was carefully peeled away, resulting in the desired composite films (Ag NWs/INPDMS–Fe-0.8).

3. Results and discussion

3.1 Preparation and characterization of elastomers

The INPDMS elastomer was first synthesized by copolymerizing PDMS-GE with IN in a 1 : 1 molar ratio. Subsequently, INPDMS–Fe-x elastomers were obtained by FeCl₃ treatment, followed by casting (Fig. 1). The chemical structures of IN and INPDMS were confirmed using Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy (Fig. S2 and S3†). The molecular weight of INPDMS was determined by gel permeation chromatography (GPC, Fig. S4†), revealing a number-average molecular weight (M_n) of 24.74 kDa. This relatively low molecular weight is sufficient to prevent excessive chain entanglement,⁵¹ thereby enhancing chain mobility and enabling fast self-healing at room temperature. These results confirm the successful preparation of IN and INPDMS.

Following the introduction of Fe³⁺, energy diffraction spectroscopy (EDS) of INPDMS–Fe-0.8 confirmed the presence of Fe in the prepared elastomer (Fig. S5†). The lack of crystalline peaks in the X-ray diffraction (XRD) pattern confirmed the amorphous state of INPMDS-Fe-0.8 (Fig. S6†). Differential scanning calorimetry (DSC) analysis revealed that INPMDS-Fe-0.8 had a higher glass transition temperature than INPDMS (Fig. S7†), consistent with the formation of a crosslinked network. Thermogravimetric analysis demonstrated that both INPDMS and INPMDS-Fe-0.8 exhibited good thermal stability (Fig. S8†). The characteristic C=C stretching vibration of INPDMS at 1593 cm⁻¹ in the FTIR spectrum underwent a significant blue shift (Fig. 2a), which is attributed to the involvement of the π-electron system of the indole derivative in complexation with Fe³⁺.⁵² The complexation of the indole derivative with Fe³⁺ also alters the π-electron density of the ring, which can be further verified by UV-vis absorption spectroscopy. As shown in Fig. 2b, the UV-vis absorption spectrum of INPDMS–Fe-0.8 exhibits a distinct absorption peak at 468 nm, corresponding to a ligand-to-metal charge transfer (LMCT) transition from the delocalized π-electron system of indole derivative to Fe³⁺.^53–55 Cation–π interactions were further investigated using UV-vis difference spectroscopy. Fig. 2c displays the absorption spectra of INPDMS and INPDMS–Fe-0.8, along with their difference spectrum. A clear pair of negative and positive bands at 233 and 244 nm, respectively, confirms the formation of cation–π interactions between Fe³⁺ and the indole derivative.^45–47 Fluorescence spectroscopy provided additional evidence of synergistic complexation and cation–π interactions. As shown in Fig. 2d, the fluorescence intensity of INPDMS–Fe-0.8 is significantly reduced, and the emission maximum blue-shifts from 450 to 443 nm compared to INPDMS, indicating the formation of the Fe³⁺–indole derivative complex and Fe³⁺–π interaction.^45–47 X-ray photoelectron spectroscopy (XPS) further confirmed the complex, evidenced by a partial reduction of Fe³⁺ to a lower oxidation state within the prepared elastomer (Fig. 2e and f).⁵⁶ To gain deeper insight into the synergistic interactions, density functional theory (DFT) calculations were performed using Materials Studio software. The electrostatic potential map revealed that the indole derivative molecule was electron-rich (Fig. 2g). The calculated highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap of the free indole derivative was 2.572 eV (Fig. 2h). Upon complexation with Fe³⁺, the energy gap dramatically decreased to 0.566 eV, indicating the formation of a stable complex.⁵⁷ This reduction in energy gap was consistent with the observed LMCT transition in the UV-vis absorption spectrum (Fig. 2b).⁵⁸ Finally, radial distribution function (RDF) analysis based on all-atom molecular dynamics simulations was used to quantify synergistic interactions. As shown in Fig. 2i, RDF peaks at 2.05 Å and 4.33 Å correspond to complexation interactions between Fe³⁺ and the indole derivative and cation–π interactions between Fe³⁺ and the indole derivative, respectively.^59,60 These results confirm the coexistence of both short-range complexation interactions and long-range cation–π interactions within the prepared siloxane elastomer.

Fig. 2 Characterization of the multiscale structure of INPDMS–Fe-x. (a) FTIR spectra of INPDMS and INPDMS–Fe-0.8. (b) UV-vis absorption spectra of INPDMS and INPDMS–Fe-0.8. (c) UV-vis difference spectra of INPDMS and INPDMS–Fe-0.8. (d) Fluorescence spectra of INPDMS and INPDMS–Fe-0.8. (e) Full-scan XPS spectra of INPDMS and INPDMS–Fe-0.8. (f) High-resolution XPS spectrum of INPDMS–Fe-0.8. (g) Electrostatic potential map of the indole derivative. (h) HOMO–LUMO orbitals of the indole derivative and its complex. (i) RDF of Fe³⁺ relative to indole groups in INPDMS–Fe-0.8.

3.2 Mechanical properties of INPDMS–Fe-x

The mechanical performance of INPDMS–Fe-x elastomers was evaluated via uniaxial tensile testing at a strain rate of 40 mm min⁻¹ (Fig. 3a). The Fe³⁺ content significantly influenced the mechanical properties of the elastomers (Fig. 3b). Among all samples, INPDMS–Fe-0.8 exhibited the optimal balance of tensile strength and elongation at break, and was therefore selected for all subsequent experiments. Specifically, compared to the uncross-linked INPDMS, INPDMS–Fe-0.8 showed a two-fold decrease in elongation at break (from 933% to 487%) but a remarkable 24-fold increase in tensile strength (from 0.12 MPa to 2.86 MPa). In particular, its toughness and Young's modulus were 8.25 MJ m⁻³ and 4.3 MPa, respectively, which were 13 times and 80 times greater than those of INPDMS, respectively (Fig. 3c). This enhancement can be attributed to the synergistic contributions of complexation interactions (short-range) and cation–π interactions (long-range) (Fig. 1). Under external stress, the dynamic Fe³⁺–π interactions serve as sacrificial bonds that efficiently dissipate energy through rapid rupture and reformation, endowing the elastomer with remarkable strength and toughness.

Fig. 3 Mechanical properties of INPDMS–Fe-x. (a) Tensile stress–strain curves of INPDMS-Fe-x samples. (b) Tensile strength results and elongation at break results for INPDMS–Fe-x. (c) Young's modulus and toughness. (d) Tensile loading–unloading curves of INPDMS–Fe-0.8 under different strains and corresponding dissipated energy (inset). (e) Tensile loading–unloading curves of INPDMS–Fe-0.8 with various rest intervals. (f) Cyclic tensile loading–unloading curves under 100% strain for 50 consecutive cycles. (g) Schematic illustration of network structure changes in INPDMS–Fe-0.8 under different strain levels.

To explore the energy dissipation behavior, tensile loading–unloading tests were conducted at strains ranging from 50% to 300% (Fig. 3d). The large hysteresis loops observed at higher strains confirmed substantial energy dissipation, which increased with applied strain. Cyclic tensile tests under 100% strain with varying resting times were conducted to evaluate elastic recovery (Fig. 3e). With increasing rest time, the stress–strain curves progressively returned to their original shape, indicating excellent elastic recovery. Conversely, when subjected to continuous loading–unloading cycles without rest (Fig. 3f), the material showed a decline in mechanical response after the second cycle, attributed to the rupture of dynamic bonds during the initial cycle and insufficient time for network reformation. Nevertheless, INPDMS–Fe-0.8 retained over 50% of its maximum stress after 50 cycles, demonstrating robust fatigue resistance under repeated deformation.⁶¹ Notably, the stress–strain curve nearly recovered to its initial form after 20 minutes of rest.

The energy dissipation mechanism is illustrated in Fig. 3g. At low strains, molecular chain mobility facilitates the slippage of indole derivative segments, allowing energy dissipation primarily via long-range Fe³⁺–π interactions. As strain increases, these Fe³⁺–π interactions rupture, releasing additional energy. Since Fe³⁺ is anchored to indole derivative units through short-range complexation interaction, it can readily reform cation–π interactions with nearby indole derivatives. This structural arrangement allows for rapid dynamic reorganization and enhances energy dissipation, preserving mechanical integrity and enabling the material to exhibit excellent elastic recovery even under large deformations. In short, the strategic incorporation of short-range complexation interactions and long-rang cation–π interactions into the elastomer networks endows INPDMS–Fe-0.8 with exceptional mechanical properties.

3.3 Self-healing and self-adhesive performance

The self-healing performance of INPDMS–Fe-0.8 was systematically investigated. To evaluate its self-healing capability, a sample was cut in half, rejoined, and incubated at room temperature. The sample healed for 8 hours could be stretched to five times its original length (Fig. 4a). To further demonstrate the room-temperature self-healing ability, a scratch-healing test was performed. A visible artificial scratch on the INPDMS–Fe-0.8 surface gradually became shallower and fully disappeared within 8 hours without the need for external stimuli such as heat or moisture (Fig. 4b). This excellent self-healing capability is attributed to the dynamic and reversible interactions within the polymer network, which can re-establish physical cross-links over time following mechanical damage (Fig. 4c). To further demonstrate the self-healing behavior, we conducted rheological tests on INPDMS–Fe-0.8. The rheological master curves were fist analyzed to examine the chain dynamics at the reference temperatures of 0 °C (near the glass transition temperature) and 25 °C (the self-healing temperature). As shown in Fig. S9a,† a distinct crossover point between the storage modulus (G′) and loss modulus (G′′) is observed. The terminal relaxation time (τ_term) calculated using the 2π/ω_term formula is relatively short for INPDMS–Fe-0.8, suggesting the rapid reconfiguration of the polymer chains.^62,63 At 25 °C, both G′ and G′′ increase with frequency, with G′′ slightly exceeding G′ (Fig. S9b†), indicating that viscous properties dominate over elasticity.⁶⁴ These results further demonstrate that dynamic and reversible interactions within the network structure endow the polymer with excellent room-temperature self-healing capability. Fig. 4d presents representative tensile stress–strain curves for the original and reconnected samples after healing. Remarkably, the sample healed for 8 hours exhibited nearly full recovery, with a self-healing efficiency of 99.30% in strain and a self-healing efficiency of 98.82% in stress (Fig. 4e). A comparative analysis was conducted against other reported self-healing systems. As shown in Fig. 4f, INPDMS–Fe-0.8 exhibits a unique combination of high mechanical performance, rapid self-healing at room temperature, and intrinsic self-adhesiveness, which surpass those of other siloxane elastomers reported in the literature.^{25,27,40,42,43}

Fig. 4 Self-healing and self-adhesive performance of INPDMS–Fe-0.8. (a) Photographs of the self-healing process at room temperature. (b) Optical microscope images showing the scratch-healing process at room temperature. (c) Schematic representation of the self-healing mechanism. (d) Typical stress–strain curves of original and healed INPDMS–Fe-0.8 after different healing times at room temperature. (e) Healing efficiency of INPDMS–Fe-0.8 in terms of stress and strain over different healing times. (f) Comparison of INPDMS–Fe-0.8 with other reported self-healing materials. (g) Photographs showing adhesion of INPDMS–Fe-0.8 to various substrates. (h) Schematic illustration of the lap-shear test setup and adhesion mechanism. (i) Adhesive performance of INPDMS–Fe-0.8 on different substrates. (j) Tensile-shear testing at different curing times. (k) Performance in repeated adhesion–separation cycles.

The self-adhesive properties of INPDMS–Fe-0.8 were systematically investigated. Our elastomer exhibited instant, good, and repeatable adhesion to diverse substrates at room temperature, including both soft and hard surfaces, such as iron, steel, glass, plastic, pigskin, wood, PMMA, rubber, and EPS (Fig. 4g). Notably, INPDMS–Fe-0.8 could bond to a steel sheet, supporting weights of 100 g after 5 minutes and 200 g after 20 minutes (Fig. S10†). Importantly, INPDMS–Fe-0.8 can be cleanly peeled off substrates without losing its adhesive properties, enabling good recyclability (Fig. S11†). Remarkably, INPDMS–Fe-0.8 also displayed robust underwater adhesion. It could adhere to various substrates underwater (Movie S1†) and effectively seal punctured surfaces to prevent leakage (Movie S2†). These exceptional adhesion properties are attributed to synergistic interactions (Fig. 4h). To assess adhesion performance, tensile shear tests were conducted on INPDMS–Fe-0.8. INPDMS–Fe-0.8 exhibited superior adhesion performance on a smooth steel plate compared to a rough wood plate (Fig. 4i). The bond strength gradually increased with increasing adhesion time. Typically, INPDMS–Fe-0.8 reached its final cured state within one day, indicating its rapid bonding (Fig. 4j). Repeated tensile shear tests on peeled adhesives demonstrated consistent bonding performance (Fig. 4k), highlighting its potential for the development of environmental-friendly adhesives.

3.4 EMI performance of composite films

Owing to the excellent self-adhesive properties of INPDMS–Fe-0.8, it readily bonds with silver nanowires (Ag NWs) to form flexible composite films suitable for electronic applications. In this study, EMI shielding films were fabricated by combining INPDMS–Fe-0.8 with high-aspect-ratio Ag NWs using a vacuum filtration and transfer method (Fig. 5a).^25–27 As shown in Fig. 5b, the Ag NWs/INPDMS–Fe-0.8 composite films retain excellent mechanical performance even after Ag NW incorporation. This is attributed to the intrinsic self-adhesiveness of the INPDMS–Fe-0.8 matrix, which ensures strong interfacial adhesion.

Fig. 5 EMI shielding performance of Ag NWs/INPDMS–Fe-0.8 composite films. (a) Schematic illustration of the fabrication process. (b) Tensile stress–strain curves of composite films with different Ag NW loadings. (c) Electrical conductivity as a function of Ag NW content. (d) EMI SE of Ag NWs/INPDMS–Fe-0.8 composite films. (e) SE_T, SE_R and SE_A of Ag NWs/INPDMS–Fe-0.8 composite films. (f) EMI SE of Ag NWs/INPDMS–Fe-0.8 composite films with 10 mg Ag NW loading after self-healing for 8 hours at room temperature. (g) SEM image showing the surface morphology of Ag NWs-10/INPDMS–Fe-0.8 after self-healing.

Electrical conductivity, a key factor influencing EMI shielding effectiveness (SE), increased with higher Ag NW content (Fig. 5c). The high conductivity of Ag NWs/INPDMS–Fe-0.8 composite films renders them highly effective for EMI shielding applications. Correspondingly, EMI SE values across the X-band (8.2–12.4 GHz) also improved with increasing Ag NW loading (Fig. 5d). Notably, even at a low loading of 2 mg Ag NWs, the composite film achieved an EMI SE of 51.4 dB (equivalent to ∼99.999% shielding efficiency) at a frequency of 8.2 GHz, surpassing the threshold for commercial applications (Fig. 5d and S12†). With a further increase in Ag NW content to 10 mg, the EMI SE increased to 70.83 dB at a frequency of 8.2 GHz. The total EMI SE (SE_T), microwave absorption (SE_A) and microwave reflection (SE_R) of Ag NWs/INPDMS–Fe-0.8 composite films calculated from scattering parameters are shown in Fig. 5e. The SE_T values of Ag NWs/INPDMS–Fe-0.8 composite films increased with Ag NW content. Analysis of reflection (R) and absorption (A) coefficients revealed that Ag NWs/INPDMS–Fe-0.8 composite films exhibited a reflection-dominated EMI shielding mechanism (Fig. S13†).

Given that mechanical damage is often inevitable during practical use, the ability of Ag NWs/INPDMS–Fe-0.8 composite films to autonomously recover their mechanical, electrical, and EMI shielding properties is particularly valuable. Like the pristine INPDMS–Fe-0.8 matrix, the composite films recovered over 90% of their mechanical strength after 8 hours of self-healing at room temperature (Fig. S14†). EMI shielding performance also demonstrated significant recoverability. After 8 hours of self-healing, the EMI SE of the composite film remained almost unchanged compared to its initial state. This recovery is attributed to the dynamic migration of the polymer chains, which enables the reorganization of the disrupted Ag NW percolation network. The SEM image (Fig. 5g) visually confirms this mechanism, showing successful reconstruction of the damaged Ag NW network after 8 hours at room temperature. Collectively, these results highlight the potential of Ag NWs/INPDMS–Fe-0.8 composite films as reliable and self-healing EMI shielding materials for next-generation flexible electronic devices.

4. Conclusions

In summary, we have successfully designed and synthesized a room-temperature self-healing and mechanically robust siloxane elastomer via synergistic complexation between Fe³⁺ and an indole derivative and cation–π interactions between Fe³⁺ and an indole derivative for EMI shielding applications. By tuning the Fe³⁺ content, the resulting INPDMS–Fe-x elastomers demonstrated outstanding mechanical performance. INPDMS–Fe-0.8 exhibited high tensile strength (2.86 MPa), outstanding elongation at break (487%) and excellent elastic recovery. The synergy between short-range complexation interactions and long-range cation–π interactions enabled remarkable room-temperature self-healing (∼99% recovery within 8 hours). In particular, INPDMS–Fe-0.8 could adhere immediately and repeatedly to various substrates at room temperature, achieving an adhesion strength of 923 kPa on stainless steel, and it also showed potential for underwater adhesion. Considering its mechanical robustness, strong adhesion, and intrinsic self-healing capability, INPDMS–Fe-0.8 was combined with silver nanowires to fabricate composite films that are highly conductive and self-healing, with excellent EMI shielding effectiveness. This work offers a novel and scalable strategy for the development of flexible electronic materials with high EMI shielding performance, paving the way for broad applications in next-generation flexible electronic devices.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the financial support from the National Natural Science Foundation of China (22006122), the Natural Science Foundation of Sichuan Province (2024NSFSC0291) and the National Innovation and Entrepreneurship Training Program for College Students (202410619031).

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ta03799a

‡ Suting Chen and Ziyi Liu contributed equally to this work.

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