Scanning electron microscopic (SEM) image of Ti3C2Tx/polystyrene composite film showing insertion of polystyrene beads within Ti3C2Tx MXene layers and (right) EMI SE versus interface area of Ti3C2/polystyrene nanocomposites. Absorption dominant EMI shielding is obvious in the plot where increasing interface area increases absorption and total EMI shielding, however reflection contribution remains constant.
Scanning electron microscopic (SEM) image of Ti3C2Tx/polystyrene composite film showing insertion of polystyrene beads within Ti3C2Tx MXene layers and (right) EMI SE versus interface area of Ti3C2/polystyrene nanocomposites. Absorption dominant EMI shielding is obvious in the plot where increasing interface area increases absorption and total EMI shielding, however reflection contribution remains constant.

A new lightweight composite material could shield electromagnetic (EM) pollution, according to researchers from Korea and the USA [Iqbal et al., Composites Science and Technology 213 (2021) 108878, https://doi.org/10.1016/j.compscitech.2021.108878 ]. Electronic devices and communications systems all produce EM radiation, which interferes and causes secondary EM pollution that degrades the performance of sensitive equipment. Shielding materials that suppress electromagnetic interference (EMI) are vital for communications systems, as well as defense and industrial equipment.

Transition metal carbides, nitrides and carbonitrides known as MXenes are now drawing attention as potential EMI shielding materials. These solution processable conductive materials are mechanically strong and combine low density with a large surface area. Moreover, MXenes can be combined with polymers, nanotubes, nanofibers, and nanowires to produce a diverse range of composites. The internal interfaces between the MXene matrix and the polymer or nanomaterial, which have very different refractive indices, scatter EM waves and lead to internal absorption.

“Absorption can be improved and systematically controlled by the microstructure of composites,” points out Chong Min Koo, who led the effort at Korea Institute of Science and Technology, Korea University, and Drexel University.

To do this, the researchers combined highly conductive two-dimensional MXene Ti3C2Tx with polystyrene beads of different sizes. While the addition of polymer beads reduces the overall conductivity of the composite, the increase in the number of internal interfaces and large difference in refractive indices between the materials boost internal scattering and absorption of EM waves. Moreover, the Ti3C2Tx/polystyrene interface creates a mini capacitor-like structure under an external electric field that improves EM absorption further.

“We set out to improve the absorption of EM waves in Ti3C2Tx/polystyrene composite films and successfully enhanced the absorption contribution by controlling the size and composition of the polymer beads,” explains Koo.

The researchers found that smaller polystyrene beads, less than 0.5 microns in diameter, have a greater effect because of the relative increase in surface area and scattering sites. The absorption factor of composites with smaller polystyrene beads is higher and better able to mitigate the effects of secondary EM pollution.

“Our Ti3C2Tx/polystyrene composite films exhibit higher absorption of EM waves because of their controlled structural design,” says Koo.

The researchers believe that the new composite films are potential candidates for EM pollution screening of highly integrated electronic devices, military equipment, and stealth technology. They are now working on improving the mechanical properties of the composite films and experimenting with other conducting materials like graphene and insulating inclusions.

“We are planning to apply this concept to many other conducting materials and polymers to find the best system for real applications,” Koo told Materials Today.