Porous polyimide-based phase change materials with enhanced mechanical properties, thermal conductivity, and thermal shock resistance through precisely designed triple-functional layers

Numerous scenarios of direct contact between electronic components and skin appear in wearable electronic devices. As the “second skin” that lies next to the biological skin of the human body, flexible wearable devices need to be equipped with thermal protection. However, the use of flexible phase change materials(PCMs) for wearable devices remains a challenge due to their low thermal conductivity, weakened mechanical strength, and liquid leakage. Herein, we developed a multilayered polyimide(PI) composite film integrating stable latent heat absorption, high thermal conductivity, and enhanced mechanical strength. This single piece of material achieved more prominent hotspot protection than traditional foams. The in-plane thermal conductivity of the resultant substrate layer is up to 2.655 W/(m K), which provides a fast response and in-plane dissipation for heat flow. The deliberately arranged interlayer of the material significantly improved the tensile strength(37.6 MPa) of the composite film,representing 128.9% greater strength than that of a bilayer film without a dense layer. The top layer with abundant pores provides reversibly latent heat storing and releasing function after being well infiltrated with paraffin wax. The resulting synergistic effect between three functional layers shows superb heat-suppressing performance in the thickness direction in both thermal shockresistant tests and simulation results. Impressively, the maximum temperature drop reached 40.2℃ compared with the pure PI film. The heating time was delayed by 12 s, providing sufficient warning time for human emergency response. This strategy can potentially pave the way for the design and fabrication of multifunctional films for wearable electronics in thermal protection applications.