Magnetic alignment of graphite platelets in polyimide matrix toward a flexible electronic substrate with enhanced thermal conductivity

A soft and stable substrate is an essential component for realizing flexible electronics and displays. We fabricated flexible substrate films by compositing iron oxide nanoparticle-conjugated graphite platelets (mGPs) with polyimide (PI). We controlled the microstructure of the composite film by aligning the mGPs with a low magnetic field in the vertical direction during the PI curing process. After magnetic alignment, the through-plane thermal conductivity of the mGP-PI composite film was enhanced by a maximum of 132% with 20 wt% mGP content compared to that without magnetic alignment. The thermal conductivity of the composite film was constant up to 300 °C and increased with the filler content, reaching 11.3 W/mK with 60 wt% mGP content. In addition, the coefficient of thermal expansion (CTE) of the composite film along the in-plane direction decreased with increasing filler content, reaching approximately 9 ppm/K with 40 wt% mGP content. This work demonstrates a pathway toward a flexible electronics substrate with high thermal conductivity, high thermal stability, and low CTE.