Development and Characterisation of Stretchable Carbon Material Composites and Their Applications

Abstract

Carbonaceous materials (e.g. graphene nanoplatelets (GNP), multi-walled carbon nanotube (MWCNT), carbon black (CB) and graphite (GRP)) have been used in many applications such as flexible electronics, energy storage devices, thermal interface devices and so on due to their excellent electrical, mechanical and thermal properties. Among them, flexible strain sensing application has been widely progressed in the recent decade. To achieve a simple and scalable fabrication process of flexible strain sensors, developing a novel, reliable patterning process of the material is demanding. In this study, flexible strain sensors were fabricated by printing and solution casting processes. Specific properties, such as the piezoresistivity, mechanical properties, durability, electrical conductivity and thermal conductivity (TC) of various carbon fillers mixed with an elastomer, silicone rubber (SR), were explored to investigate their practical applications in strain sensing and thermal interface devices. While many strain sensors have limited stretchability, this study introduces highly stretchable and super flexible strain sensors, which have shown to be applicable as wearable strain sensors for human motion detection. They have demonstrated compatibility with the human body, responsive to various body movements. This research also examines different combinations of fillers and their synergistic effect on thermal, electrical, and piezoresistive properties. The electromechanical performance of each strain sensor shows that the filler morphology plays an integral role in their behaviour. It was observed that MWCNT/SR, CB/SR and polypyrrole (PPy)/SR strain sensors displayed negative temperature coefficients of resistance while GNP/SR and GRP/SR strain sensors exhibited positive temperature coefficients of resistance. The low-temperature coefficients of resistance of the GNP-CB-SR strain sensors make them a suitable candidate for hightemperature applications. Among the various composites studied, MWCNT/SR printed strain sensor, GNP-CB-SR film strain sensor and PPy/SR film strain sensor show excellent sensor characteristics (i.e. durability, flexibility, stretchability), required for wearable strain sensors. The GNP/SR and GRP/SR composites exhibit a TC of 1.27 W m⁻¹ K⁻¹ and 1.07 W m⁻¹ K⁻¹, respectively. The stretchable, flexible, as well as soft GNP/SR and GRP/SR composite films, can transfer heat in a superior manner without affecting the mechanics of the host device, suggesting their potential application in the real world.