Absorption Dominated Directional Electromagnetic Interference Shielding through Asymmetry in a Multilayered Construct with an Exceptionally High Green Index

Synergistic Layered Design of Aerogel Nanocomposite of Graphene Nanoribbon/MXene with Tunable Absorption Dominated Electromagnetic Interference Shielding

Electromagnetic pollution presents growing challenges due to the rapid expansion of portable electronic and communication systems, necessitating lightweight materials with superior shielding capabilities. While prior studies focused on enhancing electromagnetic interference (EMI) shielding effectiveness (SE), less attention is given to absorption-dominant shielding mechanisms, which mitigate secondary pollution. By leveraging material science and engineering design, a layered structure is developed comprising rGOnR/MXene-PDMS nanocomposite and a MXene film, demonstrating exceptional EMI shielding and ultra-high electromagnetic wave absorption. The 3D interconnected network of the nanocomposite, with lower conductivity (10-3-10-2 S/cm), facilitates a tuned impedance matching layer with effective dielectric permittivity, and high attenuation capability through conduction loss, polarization loss at heterogeneous interfaces, and multiple scattering and reflections. Additionally, the higher conductivity MXene layer exhibits superior SE, reflecting passed electromagnetic waves back to the nanocomposite for further attenuation due to a π/2 phase shift between incident and back-surface reflected electromagnetic waves. The synergistic effect of the layered structures markedly enhances total SE to 54.1 dB over the Ku-band at a 2.5 mm thickness. Furthermore, the study investigates the impact of hybridized layered structure on reducing the minimum required thickness to achieve a peak absorption (A) power of 0.88 at a 2.5 mm thickness.

'Donor-acceptor', 'interpenetrating polymer network' and 'electrostatic self-assembly' work in tandem to achieve extraordinary specific shielding effectiveness

The exploration of 'electrostatic self-assembly' on solid surfaces has garnered significant interest across various fields. With the sophistication of gadgets, managing electromagnetic interference (EMI) from stray signals, especially in stealth applications, necessitates materials that can absorb microwaves. A promising approach involves integrating lightweight self-healing polymeric materials. This study employs electrostatic self-assembly to design a carbon nanotube structure on an interpenetrating polymer network (IPN) made of PVDF and bismaleimide (BMI)-grafted dopamine hydrochloride, enhancing mechanical integrity through well-formed IPNs. Graphene oxide (GO) is introduced before IPN formation to facilitate an 'acceptor-donor' interaction via the Diels-Alder adduct between BMI and GO, which binds with multi-walled carbon nanotubes (MWCNTs). MWCNTs, modified with PQ7 or PDDA for a positive charge, self-assemble onto the IPN-GO construct, creating a lightweight and chemically stable structure capable of absorbing electromagnetic radiation. The 21 μm thick construct exhibits enhanced microwave absorption within the X-band (8.2-12.4 GHz), with a specific shielding effectiveness of 8637 dB cm2 g-1 and a green index (gs ≈ 1.41). The construct is coated with self-healable polyetherimide (PEI) containing exchangeable disulfide bonds to address maintenance challenges, providing heat-triggered self-healing properties. These innovative structures offer solutions for 5G and IoT applications where lightweight, durable, and multifunctional properties are essential for effectively shielding electronic devices from stray signals.

Enhanced Mechanical and Self-Healing Properties of Carbon Fiber-Reinforced Epoxy Laminates Using In Situ-Grown ZnO Nanorods and Thermo-Reversible Bonds

Advanced hierarchical carbon fiber epoxy laminates with an engineered interface using in situ-grown ZnO nanorods on carbon fiber resulted in strong mechanical interlocking with the matrix. To further strengthen the interface, "site-specific" modification was realized by modifying the ZnO nanorods with bismaleimide (BMI), which facilitates "thermo-reversible" bonds with graphene oxide (GO) present in the matrix. The resulting laminates exhibited an improvement in flexural strength by 20% and in interlaminar shear strength (ILSS) by 28%. In order to gain a mechanistic insight, few laminates were prepared by "nonselectively" modifying the ZnO-grown carbon fiber (CF) with BMI. The "nonselectively" modified laminates showed flexural strength and ILSS improvement by 43 and 39%, respectively. The "nonselective" modification resulted in a strong improvement in mechanical properties; however, the "site-specific" modification yielded a higher self-healing efficiency (81%). Raman spectroscopy, scanning electron microscopy (SEM) micrographs, atomic force microscope (AFM) analysis, and contact angle analysis indicated a strong interaction of the modified CFs with the resin. Enhanced surface area and energy, along with a decrease in segmental molecular mobility observed from dynamic mechanical analysis, confirmed the mechanism for a better performance. Microscopic images revealed an improved interfacial behavior of the fractured samples, indicating a higher interfacial adhesion in the modified laminates. Besides mechanical properties, these laminates also showed excellent electromagnetic interference (EMI) shielding performance. The laminates with only ZnO-modified CF showed a high shielding effectiveness of -47 dB.

Layered polymer composite foams for broadband ultra-low reflectance EMI shielding: a computationally guided fabrication approach

The development of layered polymer composites and foams offers a promising solution for achieving effective electromagnetic interference (EMI) shielding while minimizing secondary electromagnetic pollution. However, the current fabrication process is largely based on trial and error, with limited focus on optimizing geometry and microstructure. This often results in suboptimal electromagnetic wave reflection and the use of unnecessarily thick samples. In this study, an input impedance model was employed to guide the fabrication of layered PVDF composite foams. This approach optimized the void fraction (VF) and the thickness of each layer to achieve broadband low reflection. Moreover, hybrid heterostructures of SiCnw@MXene were incorporated into the PVDF composite foams as an absorption layer, while the conductive PVDF/CNT composite foams served as a shielding layer. Directed by theoretical computations, we found that combining 2.2 mm of PVDF/SiCnw@MXene composite foam (50% VF) and 1.6 mm of PVDF/CNT composite yielded EMI shielding effectiveness of 45 dB, with an average reflectivity (R) of 0.03 and an effective absorption bandwidth of 5.54 GHz (for R < 0.1) over the Ku-band (12.4-18 GHz). Importantly, the corresponding peak R was only 0.000017. Our work showcases a theoretically guided approach for developing absorption-dominant EMI shielding materials with broadband ultra-low reflection, paving the way for cutting-edge applications.

A universal approach to 'host' carbon nanotubes on a charge triggered 'guest' interpenetrating polymer network for excellent 'green' electromagnetic interference shielding

The widespread use of miniaturized electronic gadgets today faces stiff reliability obstacles from factors like stray electromagnetic signals. The challenge is to design lightweight shielding materials that combine small volume and high-frequency operations to reliably reduce/eliminate electromagnetic interference. Herein, in the first of its kind, a sequential interpenetrating polymeric network (IPN) membrane was used to host a CNT construct through a stimuli-responsive trigger. The proposed construct besides being robust, sustainable, and scalable is a universal approach to fabricate a CNT construct where conventional strategies are not amenable. This approach of self-assembling counter-charged CNTs also maximizes the number of CNTs in the final construct, thereby greatly enhancing the shielding performance dominated by 90% absorption in a wide frequency band of 8.2-26.5 GHz. The IPN-CNT construct achieves specific shielding effectiveness in the range of ca. 1607-5715 dB cm² g^-1 by tuning the thickness of the CNT construct with an endearing green index (g_s ≈ 1.8). The performance of such an ultra-thin, light-weight IPN-CNT construct remained unchanged when subjected to 10 000 bending cycles and on exposure to different chemical environments, indicating outstanding mechanical/chemical stability.