Hierarchical electroactive polypyrrole-carbon nanotube composite microstructures by high resolution vat polymerization and soft template electropolymerization

The Organic Mechatronics and Smart Materials Laboratory has previously reported a photosensitive electroactive polypyrrole (PPy) composite resin. The photosensitivity of this resin overcame common issues associated with conjugated polymer device fabrication such that complex 3D structures can now be fabricated via light-based additive manufacturing methods. While this resin formulation enabled the fabrication of previously achievable structures and devices, it also required the introduction of copolymers bisphenol A ethoxylate dimethacrylate and polyethylene glycolmethyl ether methacrylate (BEMA-PEGMA). These copolymers improved the mechanical stability of 3D structures with a concomitant trade-off with the electroactive properties of the composite. This study investigates the introduction of PPy coated carbon nanotubes (CNTs) to improve the electrical and electrochemical properties of the composite material. The effect on performance of the composite was investigated by creating stable dispersions of PPy-CNTs at loading factors from 1 - 9 mg/mL directly into the pyrrole monomer. The electrical conductivity, electroactive response, and suitability for 3D fabrication of the composite has been assessed. 3D transducers fabricated using this new formulation are shown to exhibit feature resolution comparable to the original resin formulation. Finally, the improved electrical conductivity of the material is assessed to enable the post-hoc deposition of PPy microstructures via soft template electropolymerization. In this process, hydrogen gas bubbles are formed on the working electrode of 3-electrode electrochemical cell, and upon subsequent application of a positive potential PPy is polymerized around the bubble templates. The resulting hierarchical PPy microstructures on the vat polymerized composite films are shown to increase surface area and consequently improve electroactive response.