Adhesion enhancement of conductive graphene/PI substrates through a vacuum plasma system

Abstract

Flexible electronics is regarded as a promising solution to stretchable/wearable devices given its light weight and high deformation ability. As a conducting layer, a widely utilized transparent conducting film, namely, indium tin oxide (ITO), is approaching its limitation on flexible applications given its high stiffness and brittle characteristics. Thus, this study proposes a highly flexible bi-layered architecture composed of polyimide (PI) substrate and coated graphene ink. This architecture is considered to replace the foregoing ITO film. A vacuum plasma system with different treatment parameters is taken into account to enhance the interfacial adhesion of graphene/PI substrates. Furthermore, a fracture-based finite element model of patterned graphene/PI substrates with various line widths are constructed to ensure the applicability of the presented stacked structure to actual flexible applications. This model aims to analyze the interfacial cracking energy under several designed bending radii of curvature through a modified virtual crack closure technique. To determine the fractured criterion of graphene/PI interfacial adhesion, a series of pull-off and lap shear tests are performed while requiring a comparison with simulated predictions. Results show that the peeling mode dominates the interfacial delamination of graphene/PI substrates, and the critical pull-off energy is appropriated to judge the fractured occurrence in accordance with the corresponding results of experimental bending tests. The adoption of vacuum plasma treatment contributes to enhancing the interfacial adhesion of the concerned interface and preventing the delamination failure occurrence during operating flexural loads.