High thermally conductive polyimide film designed with heterostructural Cring-C3N4 filler and multilayer strategy

Abstract

With the emerging of advanced flexible electronic, the PI film with excellent thermally conductive, flexible, lightweight, electrically insulating qualities is in high demand as a potential substrate and encapsulation material. Conventional thermally conductive fillers such as ceramic, metal and carbon material with high hardness, high density or electrical conductivity are unsuitable to prepare the advanced PI film. Furthermore, the confined loading of thermally conductive filler in PI matrix limited by its film-forming property is another obstacle to optimizing the thermal conductivity of PI film. In this work, the development of novel filler (carbon nitride in-plane grafted by two-dimensional carbon material, Cring-C3N4) with intrinsic thermal conductivity and a design of three-layer structure for the introduction of high filler loading have dramatically improved the thermal conductivity of PI film. Benefitting by the planar heterostructure construction of g-C3N4 and Cring, the existence of Cring increases the phonon transfer rate in g-C3N4, and the presence of g-C3N4 prevents the electron movement in the facet of Cring-C3N4 endowing its excellent electrical insulation property. The design of three-layer structure in which the first and third layers served as mechanical support layers with a fixed filler content (20 wt%). The second layer has the higher filler content to enhance the quantity of thermally conductive filler in PI film. Resultantly, the maximum out-of-plane thermal conductivity of the PI/Cring-C3N4 composite film is 1.35 Wm−1K−1, which is 10 times higher than the pure PI film. In addition, the PI/Cring-C3N4 composite film exhibit excellent photothermal conversion ability in which the saturation temperature of PI/Cring-C3N4 can reach 283.6 °C under 0.75 W/cm2 laser radiation being 6 times higher than that of the corresponding PI film. After the incorporation of Cring-C3N4, the PI composite film still has excellent thermal stability, low CTE, electrical insulation and mechanical properties. This work provides a novel idea for the preparation of advanced high thermal conductivity PI film.