Carbon nanotube/ZnO nanowire/polyvinylidene fluoride hybrid nanocomposites for enhanced electromagnetic interference shielding

Microwave-assisted ZnO-decorated carbon urchin resembling 'shish-kebab' morphology with self-healing and enhanced electromagnetic shielding properties

Herein, inspired by Acacia auriculiformis fruit, the shish-kebab-like growth of ZnO on carbon urchin (ZnO@CU) was designed using microwave radiation, thus leading to a hierarchal 3D structure that can promote multiple internal reflections through polarization centers. This hierarchal structure was then dispersed in a designer polyetherimide (PEI) matrix containing dynamic covalent bonds that can undergo metathesis, triggered by temperature, to harness self-healing properties in the composite. Such key attributes are required for their potential use in EMI shielding applications where frequent repairs are indispensable. Morphological investigation revealed that the ZnO flower was periodically nucleated like 'shish-kebab' structures on CU surfaces. CU was designed from short carbon fibers using a facile modified method. The EMI shielding performance of the resulting composites was investigated in the X-band, illustrating a shielding effectiveness of -40.6 dB for 2 wt% of ZnO@CU loading, and the composite can be preserved after the self-healing procedure. The ZnO 'kebabs' on 'CU shish' facilitated multiple scattering and numerous polarization centers to improve the EMI shielding performances at extremely low filler contents. In addition, the mechanical and thermal properties of the composite showed improved structural integrity and superior resistance to extreme temperatures, respectively. Overall, the proposed ZnO@CU/PEI composite has great potential to fulfill the increasing demands for lightweight EMI shielding materials in many fields.

Lightweight ZnO/Carbonated Cotton Fiber Nanocomposites for Electromagnetic Interference Applications: Preparation and Properties

Electromagnetic wave pollution has become a significant harm posed to human health and precision instruments. To shelter such instruments from electromagnetic radiation, high-frequency electromagnetic interference (EMI) shielding materials are extremely desirable. The focus of this research is lightweight, high-absorption EMI shielding composites. Simple aqueous dispersion and drying procedures were used to prepare cotton fiber (CF)-based sheets combined with various zinc oxide (ZnO) contents. These composites were carbonated in a high-temperature furnace at 800 °C for two hours. The obtained CF/ZnO samples have densities of 1.02-1.08 g/cm3. The EMI shielding effectiveness of CF-30% ZnO, CF-50% ZnO, and CF-70% ZnO reached 32.06, 38.08, and 34.69 dB, respectively, to which more than 80% of absorption is attributed. The synergetic effects of carbon networks and surface structures are responsible for the high EMI shielding performance; various reflections inside the interconnected networks may also help in improving their EMI shielding performance.

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.

Mechanical, Thermal, Electrical Characteristics and EMI Absorption Shielding Effectiveness of Rubber Composites Based on Ferrite and Carbon Fillers

In this work, rubber composites were fabricated by incorporation of manganese-zinc ferrite alone and in combination with carbon-based fillers into acrylonitrile-butadiene rubber. Electromagnetic parameters and electromagnetic interference (EMI) absorption shielding effectiveness of composite materials were examined in the frequency range 1 MHz-3 GHz. The influence of ferrite and fillers combination on thermal characteristics and mechanical properties of composites was investigated as well. The results revealed that ferrite imparts absorption shielding efficiency to the composites in tested frequency range. The absorption shielding effectiveness and absorption maxima of ferrite filled composites shifted to lower frequencies with increasing content of magnetic filler. The combination of carbon black and ferrite also resulted in the fabrication of efficient EMI shields. However, the EMI absorption shielding effectiveness was lower, which can be ascribed to higher electrical conductivity and higher permittivity of those materials. The highest conductivity and permittivity of composites filled with combination of carbon nanotubes and ferrite was responsible for the lowest absorption shielding effectiveness within the examined frequency range. The results also demonstrated that combination of ferrite with carbon-based fillers resulted in the enhancement of thermal conductivity and improvement of mechanical properties.