Abstract
Self-supported conducting polymer films with controlled microarchitectures are highly attractive from fundamental and applied points of view. Here a versatile strategy is demonstrated to fabricate thin free-standing crack-free polyaniline (PANI)-based films with stable wrinkling patterns. It is based on oxidization polymerization of pyrrole inside a pre-wrinkled PANI film, in which the wrinkled PANI film is used both as a template and oxidizing agent for the first time. The subsequently grown polypyrrole (PPy) and the formation of interpenetrated PANI/PPy networks play a decisive role in enhancing the film integrity and the stability of wrinkles. This enhancing effect is attributed to the modification of internal stresses by the interpenetrated PANI/PPy microstructures. Consequently, a crack-free film with stable controlled wrinkles such as the wavelength, orientation and spatial location has been achieved. Moreover, the wrinkling PANI/PPy film can be removed from the initially deposited substrate to become free-standing. It can be further transferred onto target substrates to fabricate hierarchical patterns and functional devices such as flexible electrodes, gas sensors, and surface-enhanced Raman scattering substrates. This simple universal enhancing strategy has been extended to fabrication of other PANI-based composite systems with crack-free film integrity and stabilized surface patterns, irrespective of pattern types and film geometries.
Highlights
As a typically non-lithographic micro/nano-fabrication method, surface wrinkling has attracted intense interest owing to its simplicity, universality, low cost and so on[8,9,10,11]
The disappearance of surface wrinkles and appearance of cracks happen once the wrinkled PDMS(n:1)/PANI film is dried (II)
The wrinkled PANI film is converted into the fully oxidized state of pernigraniline base (PB), and acts both as the template and oxidizing agent to induce the oxidative polymerization of pyrrole into PPy (III)
Summary
As a typically non-lithographic micro/nano-fabrication method, surface wrinkling has attracted intense interest owing to its simplicity, universality, low cost and so on[8,9,10,11] This instability-driven patterning usually occurs on a film/substrate bilayer system with a rigid film bound to a compliant substrate (e.g., polydimethylsiloxane (PDMS)), once the driving force exceeds the bilayer material-defined critical value. Based on this intrinsic stress-relief characteristic, different surface wrinkling morphologies (e.g. herringbone, labyrinth and dimple) and switchable wrinkled/dewrinkled surfaces have been obtained by changing the stress state of the film/substrate system[13,14,15] These instable patterns have internal limitations when involved in specific fields such as friction[16] and contact[17]. This work will pave the way to fabricate various self-supported crack-free patterned films for multi-functions and unprecedented applications
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