Study of conductive and self-healing nanostructured films for application in flexible electronics

Author(s)

Gabriel Gaál

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2022-04-29

Examining board members

Varlei Rodrigues; Francisco das Chagas Marques; Italo Odone Mazali; Lucas Fugikawa Santos; Gregório Couto Faria

• Advisor: Varlei Rodrigues

Abstract

The controlled engineering of polymeric materials allows the development of new multifunctional interfaces with unique properties for various technological applications. In this context, the integration of self-healing properties with electrical conductivity allows the development and integration of biomimetic devices such as electronic skins, creating a seamless interface between biological and electronic materials. In the present work, we explored the integration of graphene-based hybrid materials, conductive polymers and self-healing materials to develop these interfaces. These structures were layer-by-layer (LbL) assembled by physical adsorption. This LbL technique allows the development of distinct molecular architectures by exploring different properties of materials for the creation of multifunctional nanostructures having unique properties. In the first part of this work we present the characterization of the self-healing matrix composed by poly(iminoethylene) (PEI) and poly(acrylic acid) (PAA). We associate the exponential and linear growth regimes of (PEI/PAA) with changes in the electrical characteristics acquired after each step of the LbL film formation. We demonstrated the central role of trapped water on the electrical, mechanical and morphological properties of such films. At the same time, together with Prof. Antônio Riul Júnior, we studied the electrical and mechanical properties of conductive and self-healing films based on (PEI/PAA) doped with reduced graphene oxide (rGO) sheets, poly(3, 4-ethylenedioxythiophene) sulfonated polystyrene (PEDOT:PSS), Multi Walled Carbon Nanotubes (MWCNTs) and gold nanorods. We showed that the insertion of these materials does not change the intrinsic self-healing ability of such materials. We then developed an electronic tongue device that was able to distinguish the five basic tastes, in addition to distinguishing different levels of glucose in samples of artificial sweat. We used such conductive and self-healing films to develop a biosensor capable of detecting the ex-vivo heartbeat of a zebrafish, with a signal-to-noise ratio of 30 dB. We also verified that composite LbL films of (PEI/PAA) doped with rGO and PEDOT:PSS show high electrical anisotropy. We observed an in-plane conductivity 5 orders of magnitude higher than the cross-plane value, resulting in the highest anisotropic ratio reported to date for multilayered materials. We explored such high anisotropic electrical behavior in a novel transistor architecture where the anisotropic film operates simultaneously as a dielectric layer and as transistor semiconductor channel, with the cross-plane electric field modulating the in-plane conduction. Finally, we used these same films to study the impact of PEDOT:PSS and water trapped in composite film structures on their supercapacitive properties. We showed that the capacitance of as prepared films depends on the amount of PEDOT:PSS in the film structure, however, in hydrated films, the water trapped in the materials, dominates the electrical response of the devices (AU)

• FAPESP's process: 17/19862-3 - Study of nanostructured conducting and self-healing films for flexible electronics application
• Grantee: Gabriel Gaál
• Support Opportunities: Scholarships in Brazil - Doctorate