In the Information Age, electronic devices are almost everywhere - pushing developers and researchers to find lighter and more flexible materials that could prevent interference between devices and minimize radiation exposure to humans.
A team of engineers from the University of California, Riverside reported in the latest edition of Advanced Materials the existence of a polymer-based flexible film using quasi-one-dimensional nanomaterial fillers that are surprisingly easy to manufacture and can shield from electromagnetic radiation.
Electromagnetic Radiation Shielding
"These novel films are promising for high-frequency communication technologies, which require electromagnetic interference shielding films that are flexible, lightweight, corrosion resistant, inexpensive, and electrically insulating," explains Alexander A. Balandin, senior author of the study and a distinguished professor of electrical and computer engineering at the Rosemary Bourns College of Engineering at UC Riverside, in a press release.
Electromagnetic interference (EMI), refers to the overlapping of signals - usually from different electronic devices - causing distortion and affecting performance. The most common example includes mobile devices like smartphones and tablets causing static on older television models. This also explains the existence of Airplane Mode on cellphones, which completely cuts off a mobile device's connectivity (BlueTooth, SMS/ MMS, Wi-Fi) to prevent interfering with navigation signals and instrumentation onboard airplanes.
While the existence and nature of EMI have long been discovered, shielding against this phenomenon has remained open to improvements - mainly because conventional shielding devices remain insufficient. Furthermore, more electronic devices in daily living mean humans are getting exposed to greater amounts of electromagnetic radiation. This prompts the need for better shielding materials.
Fabricating a Polymer Flexible Film Shield Against EMI
Balandin and the UC Riverside team used unusual fillers - chemically exfoliated bundles of quasi-one-dimensional van der Waals materials. These are materials composed of strongly-bonded 2D layers that, together, create a 3D structure based on weak dispersion forces. In a scalable synthesis of these composites, researchers created a material that has exception EMI shielding capabilities reaching gigahertz (GHz) and near-terahertz (THz) frequency range, and electrical insulation - properties that could prove significant for the next generation electronics and communications.
Perhaps the most well-known van der Waals material is graphene, which exists as a 2D sheet of strongly bound Carbon atoms. Several of these graphene sheets, coupled together by weaker van der Waals forces, create a bulk graphite crystal.
On the other hand, researchers have also inquired into one-dimensional van der Waals materials, which are bound by strong atomic forces instead of planes that have weaker binding forces. The UC Riverside team, for example, have led pioneering studies of these one-dimensional materials and their unusual properties.
This new and unique composite material was synthesized by doctoral student Zahra Barani and research professor Fariboz Kargar, who also works as a project scientist with Balandin's Phonon Optimized Engineered Materials (POEM) Center. They treated transition metal trichalcogenides - a van der Waals materials that maintain a quasi-one-dimensional crystal structure - using chemicals that made it shed needle-like nanowires.
"There was no standard recipe for exfoliation of these materials. I did many trial and error experiments, while checking the cleavage energy and other important parameters to exfoliate them with high yield," Barani recalls. He adds that the key is to get bundles of these quasi-one-dimensional materials with aspect ratios as high as possible, explaining that electromagnetic waves couple better with longer and thinner strands.
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