In the electromagnetic spectrum, the Terahertz (THz) frequency band is sandwiched between the microwaves and the infrared. THz radiation travels in a straight line and is non-ionizing. Materials with low polarizability such as plastics absorb THz weakly, those of strong electric polarizability absorb THz radiation substantially, while those of high electrical conductivity act like mirrors and reflect THz radiation highly. Over the years, THz radiation with unique properties has been long studied and stimulated the rapid development of terahertz technologies in various fields. Consequently, the need for electromagnetic interference (EMI) shielding materials toward terahertz radiation has emerged and is required to eliminate radiation leaks and create safe electromagnetic environments. This will ensure delicate electronic devices work properly. In essence, it has been shown that the shielding materials should possess flexibility, minimal thickness, and high shielding efficiency (SE) to meet the increasingly stringent requirements. However, to date, realizing efficient EMI shielding with negligible reflection in an ultrathin shielding material is still rarely reported. In addition, once fabricated, conventional shielding materials exhibit fixed shapes and cannot be re-edited and recycled or recover from damage, impeding the application flexibility and reliability.
Generally, despite tremendous breakthroughs in achieving superb shielding efficiency (SE), conventional shielding materials have high reflectivity and cannot be re-edited or recycled once formed. This results in detrimental secondary electromagnetic pollution and poor adaptability. Therefore, to confront these challenges, a pioneering alternative strategy for developing next-generation high-performance shielding materials beyond the usual design strategies is urgently needed to meet the escalating demands of the increasing complexity of modern devices and service environments. In this regard, researchers from the Trinity College Dublin: Professor Valeria Nicolosi, Dr. Ji Liu and Dr. Jing Jing Wang, in collaboration with Dr. Tong Guo and Professor Xiuzhi Tang at the Central South University, Yunyi Zhu at the Hunan University, designed a new fabrication for hydrogel-type shielding material incorporating MXene and poly (acrylic acid), via a biomineralization-inspired assembly route. The original article is currently published in the research journal, ACS Nano.
Their strategy involved assembling Ti3C2Tx MXene sheets through a biomineralization-inspired assembly method to fabricate a hydrogel-type shielding material with a hybrid structure consisting of MXene, poly (acrylic acid) (PAA), and amorphous calcium carbonate (ACC) (MXene-PAA-ACC). Various characterization techniques, such as SEM, XPS, and XRD were employed to characterize the new designed material. A silicon-on-sapphire photoconductive antenna was also used to detect the terahertz signals during the terahertz shielding and absorption measurements.
The authors reported that the composite hydrogel exhibited excellent stretchability and recyclability, favorable shape adaptability and adhesiveness, and fast self-healing capability, demonstrating great application flexibility and reliability. More interestingly, the shielding performance of the hydrogel showed an absorption-dominated feature due to the combination of the porous structure, moderate conductivity, and internal water-rich environment.
In summary, the study developed a multifunctional MXene composite hydrogel with excellent stretchability and recyclability, favorable shape adaptability and adhesiveness, fast self-healing ability, and sensing capability to provide efficient terahertz EMI shielding. Remarkably, the synergy among the moderate conductivity, porous structure, and internal water-rich environment was seen to enhance the hydrogel with absorption-dominated EMI shielding performance. In a statement to Advances in Engineering, Professor Valeria Nicolosi explained their work provides not only an alternative strategy for designing next-generation EMI shielding material but also a highly efficient and convenient method for fabricating MXene composite on macroscopic scales.
Yunyi Zhu, Ji Liu, Tong Guo, Jing Jing Wang, Xiuzhi Tang, Valeria Nicolosi. Multifunctional Ti3C2Tx MXene Composite Hydrogels with Strain Sensitivity toward Absorption-Dominated Electromagnetic Interference Shielding. ACS Nano 2021, volume 15, page 1465−1474.