Ionic liquid-functionalized reduced graphene oxide–aramid nanofiber composite films for enhanced thermal conductivity, electromagnetic interference shielding, and mechanical properties

The escalating integration of wireless technologies and compact electronic devices has intensified the demand for high-performance, light weight, thermally conductive and flexible electromagnetic interference (EMI) shielding materials. In this work, 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), a hydrophilic ionic liquid (IL), was used to non-covalently functionalize reduced graphene oxide (rGO), which was further incorporated into an aramid nanofiber (ANF) matrix by vacuum-assisted filtration to fabricate rGO@IL/ANF composite films. Non-covalent functionalization with the IL enhanced dispersion stability while maintaining the intrinsic π-conjugated structure of rGO. Furthermore, the IL improved the interfacial compatibility between rGO and the ANF matrix, promoting the formation of well-aligned, densely packed conductive networks. Consequently, the composite film exhibited an improved EMI shielding effectiveness (EMI SE) of 35 dB in the X-band (8-12 GHz) and a high in-plane thermal conductivity (TC) of 82 W m^-1 K^-1 at a thickness of 30 μm, representing improvements of 45.8% and 54.7%, respectively, compared to the rGO/ANF composite film. Furthermore, the composite film exhibited excellent mechanical properties with a tensile strength of 237 MPa and a Young's modulus of 9.92 GPa corresponding to enhancements of 196.3% and 18.24%, respectively, compared to the rGO/ANF composite film. The rGO@IL/ANF composite film also exhibited long-term performance stability under harsh environmental conditions. This study highlights that IL-functionalized rGO can serve as a practical solution for fabricating high-performance composites in flexible electronic applications.