Crack propagation design in transparent polymeric conductive films via carbon nanotube fiber-reinforcement and its application for highly sensitive and mechanically durable strain sensors

Abstract

Conductive thin films are typically subject to crack formation and propagation under tensile strain, turning into insulating films due to complete breakage at large strain. However, if such crack propagation can be intentionally designed, repetitive resistance change can be obtained and used for implementation of high-performance strain sensors that are suitable for biocompatible and stretchable electronic applications. In this work, therefore, we introduce a fiber-reinforced region, which is formed by additionally inkjet-printing a single-walled carbon nanotube thin film, in a poly(3, 4-ethylenedioxythophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS) thin film. The fiber-reinforced region well suppresses the crack propagation in the film under the tensile strain. The engineered PEDOT:PSS films are used to fabricate a strain sensor with a high gauge factor of ∼9 (at 50% strain) and an excellent working range of 70% even after 1000 cycle test at 50% tensile strain. Such a high-performance is explained via different fracture mechanisms between the fracture-designed and the fiber-reinforced regions in the PEDOT:PSS films. Our strategy of designing crack propagation using the inkjet-printing process enables not only to fabricate high-performance strain sensors that can detect human motions but also to provide a new insight for highly contuctive, but relatively brittle, materials toward the stretchable electronics applications.