Bioinspired Fabrication of Free-Standing Conducting\nFilms with Hierarchical Surface Wrinkling Patterns

Abstract

Mechanical instability has been shown\nto play an important role\nin the formation of wrinkle structures in biofilms, which not only\ncan adopt instability modes as templates to regulate their 3D architectures\nbut also can tune internal stresses to achieve stable patterns. Inspired\nby nature, we report a mechanical–chemical coupling method\nto fabricate free-standing conducting films with instability-driven\nhierarchical micro/nanostructured patterns. When polypyrrole (PPy)\nfilm is grown on an elastic substrate <i>via</i> chemical\noxidation polymerization, differential growth along with <i>in\nsitu</i> self-reinforcing effect induces stable wrinkle patterns\nwith different scales of wavelengths. The self-reinforcing effect\nmodifies the internal stresses, hence PPy films with intact wrinkles\ncan be removed from substrates and further transferred onto target\nsubstrates for functional device fabrication. To understand the buckling\nmechanics, we construct a model which reveals the formation of hierarchical\nwrinkle patterns.