Preparation of highly thermally conductive polyimide film with hexagonal alumina flakes

The power density of flexible electronics, foldable devices and wearable devices is becoming increasingly high, posing higher requirements for the out-of-plane thermal conductivity of flexible substrates. This paper reports a polyimide (PI) film with excellent out-of-plane thermal conductivity and flexibility prepared with homemade hexagonal alumina (h-Al 2 O 3 ) flakes. With higher crystallinity, more regular geometry and larger diameter-thickness ratio, self-prepared h-Al 2 O 3 is more likely to lap out-of-plane to form a continuous and efficient heat conduction network. The PI/ h-Al 2 O 3 composite film exhibits higher thermal conductivity than that of PI/commercial spherical alumina (c-Al 2 O 3 ) composite film at the same mass fraction. The out-of-plane thermal conductivity of the PI composite film loaded with 40 % h-Al 2 O 3 reaches 1.53 Wm −1 K −1 , 1.91 times higher than that of PI/ c-Al 2 O 3 composite film (0.80 Wm −1 K −1 ). Additionally, PI/h-Al 2 O 3 composite film exhibits excellent electrical insulation, high flexibility and enhanced thermal stability. This work provides an effective method to address the deficiency of out-of-plane thermal conductivity of PI film.