Flexible electromagnetic interference shields made of silver flakes, carbon nanotubes and nitrile butadiene rubber

The recent advances in portable and flexible electronic devices demand integration of flexibility into future electromagnetic interference shielding materials. Here we synthesized flexible adhesive shields made of microscale silver flakes (Ag flakes), multi-walled carbon nanotubes decorated with nanoscale silver particles (nAg-MWNTs), and nitrile butadiene rubber (NBR). The addition of nAg-MWNTs into the Ag flake-NBR mixture significantly enhanced both conductivity and shielding effectiveness. Long nanotubes electrically linked microscale Ag flakes embedded in the NBR matrix, and nanoscale silver particles further improved the contact interface. There was a logarithmic relationship between the conductivity and shielding effectiveness. The dominant mechanism of electromagnetic interference shielding was reflection. The achieved maximum shielding effectiveness was about similar to 75 dB at 1 GHz. The flexible adhesive shield printed on a polyimide film was wrapped around a cylindrical rod with a radius of 4 mm. The shielding effectiveness decreased about 20% after 100 wrapping cycles. The conductivity and shielding effectiveness could be adjusted by changing the Ag flake concentration. There was an excellent agreement between the theoretically predicted shielding effectiveness and the experimental data. (C) 2013 Elsevier Ltd. All rights reserved.