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.