A better shield

University of Virginia engineering professor Mool C. Gupta and his team have used carbon nanotubes to unite the virtues of plastics and metals in a new ultra-lightweight, conductive material that may revolutionise electromagnetic shielding.

Sensitive electronic devices like cell phones and computers require shielding from electromagnetic interference (EMI). Such shielding - which must be electrically conductive - has traditionally been made of metal, which poses a weight problem in the push to miniaturise and lighten electronics. In response, Gupta led a team that has developed an ultra-lightweight nanocomposite that outperforms conventional shielding.

This new nanocomposite material is a mixture of plastic, carbon nanotubes and a foaming agent, making it extremely lightweight, corrosion-proof and cheaper to produce than metal. The carbon nanotubes play a key role in creating these unique properties, explained Gupta.

Most notably, experiments revealed that only 1 percent to 2 percent of the material's composition needed to be comprised of nanotubes to increase the electrical conductivity by 10 orders of magnitude. The addition of carbon nanotubes also increased the material's thermal conductivity, improving its capacity to dissipate heat.

‘Metal is not only heavy; it corrodes easily,’ Gupta said. ‘And plastic insulators are lightweight, stable and cheaper to produce, but cannot conduct electricity. So the goal, originally, was to take plastic and make it electrically conductive.’

After experimenting with adding metal powder to plastics without impacting the weight of the material significantly, Gupta turned to carbon nanotubes.

With their ultra-small diameter, high aspect ratio, high mechanical strength, good electrical and thermal conductivity and light weight, Gupta and his team found that carbon nanotubes had all of the properties necessary to accomplish the objective.

‘The long length and small diameter of carbon nanotubes forms an interconnectivity within the plastic that makes it electrically conductive,’ said Gupta. ‘The structures work well for electromagnetic interference shielding. Once we reached this milestone, we began investigating ways to reduce the weight even further.’

Gupta's team then added a foaming agent - a chemical that creates air pockets - to the material. The results astounded even the researchers; this extra step reduced the weight of the material by 50 percent and increased its flexibility.