Flexible, Stretchable, and Thin Films Based on Functionalized Carbon Nanofiber/Graphene Nanostructures for Electromagnetic Interference Shielding

Flexible electromagnetic shielding materials (ESMs) are becoming progressively important to flexible and conformal electronic devices operating in civil, aerospace, and military industries. There is a legitimate need to fabricate flexible, thin, featherweight, and stretchable materials with higher electromagnetic interference shielding effectiveness (EMI SE) that can handle harsh environments. Graphene nanoplatelets (GNPs) are synthesized by microwave-supported exfoliation of graphite proceeded by water-bath sonication, whereas functionalized carbon nanofibers (FCNFs) are synthesized via acid functionalization using HNO3. The effects of conventional CNF, FCNF, and GNP are observed by embedding in the polyurethane (PU) matrix to obtain flexible, highly stretchable (>400%), lightweight, and thin (300 mu m) nanocomposites for enhanced EMI shielding performance. The GFCNF/PU nanocomposite showed uniform distribution and excellent microwave properties at low weight%. An improvement in the total EMI SE (SET) value is noticed by adding GNP (2, 4, and 6 wt %) in FCNF4, and a maximum SET value of 60.55 dB is obtained for FCNF/GNP (4/6 wt %). A negligible change in the value of EMI SE is observed after 500 mechanical bending cycles and bathsonicating the nanocomposites in distilled water, confirming the efficiency of operating in the complex environmental condition. Further, the value of SET is measured by placing the nanocomposites at different bending radii inside the waveguide to verify the practical applicability of fabricated nanocomposites in conformal devices. EMI shielding is also calculated for nanocomposites through simulation in the CST microwave studio tool (in the X-band), further extending the analysis for broadband frequency (1- 18 GHz).