A multifaceted heat-switching nanofiller: Design of heat dissipation–insulation switching materials above a critical temperature

As the technological evolution of device miniaturization in electronics continues, interfacial heat management is becoming increasingly crucial for protecting device functionality. Thermal gap fillers are widely used as thermal interface materials (TIMs) because of their high thermal conductivities. However, these fillers primarily dissipate heat and lack insulation properties, making the devices vulnerable to situations such as electrical fires or explosions. In this study, we introduce a multifaceted nanofiller with heat dissipation–insulation switching properties achieved by functionalizing magnetic nanoparticles with flame-retardant biopolymers. The resulting heat-switching nanofiller demonstrates high heat dissipation properties (>0.467 W m⁻¹ K⁻¹) and thermal stability in the epoxy matrix. Importantly, heat transfer occurs effectively in one direction owing to the magnetic alignment of the particles. Moreover, the heat-switching nanofiller forms a nano-char as a heat insulation layer, exhibiting significant insulation properties (<0.171 W m⁻¹ K⁻¹) above 300 °C. Additionally, the nanofiller achieves a high rating in standard flame-retardant tests (UL94 V-0) and a limited oxygen index of 32.7 %, while reducing CO release by 60.4 %. These results suggest that our heat-switching nanofiller can transition from heat dissipation to insulation above a critical temperature, thereby offering a promising solution to the challenges faced by TIMs in electronics.