Tough polyimide composites synergistically reinforced by carbon nanofiber-grafted carbon fiber and rGO for improved heat dissipation and electromagnetic interference shielding

The rapid miniaturization and a consequent increase in electromagnetic wave(EM)and heat emission in integrated electronic devices are now urgently desiring for multifunctional polymer composites that simultaneously possess high mechanical properties,excellent electromagnetic interference(EMI)shield-ing ability and heat dissipation capability.Herein,a series of novel polyimide-based composite films were constructed by rationally assembling the carbon nanofiber-grafted carbon fiber(NCF)and reduced graphene oxide(rGO)into a highly electrically and thermally conductive pathway within polyimide ma-trix via a sequential bidirectional freezing casting and hot-pressing strategy.The combination of high tensile strength and toughness was obtained by incorporating rGO into the NCF-reinforced PI composite,giving rise to a hierarchical reinforcing structure of NCF and crack deflection induced by rGO nanosheets.The high electrical conductivity(7.0×10^(3) S m^(-1))endows the PI/NCF30/rGO3.5 composite film with a good EMI shielding effectiveness of 45 dB.Moreover,the well-aligned thermally conductive NCF and rGO and strong interfacial bonding between the polymer matrix and reinforcing fibers give rise to improved thermal conductivity(λ),particularly along the in-plane direction.Typically,the PI/NCF30/rGO3.5 exhibits an in-plane thermal conductivity of 5.18 W m^(-1) K^(-1),∼4.7 times increment compared to the pure PI(0.91 W m^(-1) K^(-1)).Besides,the resultant PI/NCF30/rGO3.5 composite film presents a superior Joule heat-ing performance with some features of fast thermal response,ease of regulation and sufficient reliability.Accordingly,the developed multifunctional polyimide-based composite films demonstrate high potential as advanced EMI shielding materials with excellent heat dissipation.