Influence of stretching on the properties of laser-induced graphene on polyurethane strain sensors

In today’s digital age, the interest in wearable electronics has been growing distinctively. However, the fabrication of lightweight, stretchable and reasonably priced conductors is still challenging. Due to its high electrical conductivity, and three-dimensional porous structure, laser-induced graphene (LIG) is predestined as one of the active materials of choice in flexible sensors. With the laser-induced transformation of carbonic precursors, a low-cost, time-efficient, facile and scalable production technique of graphene like materials has emerged. Herein, we used this method to generate laser-induced graphene on the surface of polyimide (PI) using a CO2 laser with a wavelength of 10.6 µm and subsequently transferring the pattern to Fixomull®, a commercial medical grade polyurethane (MPU). Afterwards, a detailed characterization of the elastomeric conductive polymer composite LIG/Fixomull under different deformation levels was performed. Scanning electron microscopy (SEM), Raman spectroscopy and van der Pauw sheet resistance measurements gave a better understanding of the performance of the LIG-based strain sensor as a function of the stretching degree in correlation to the changes that the porous structure of the material was undergoing. Our flexible LIG/Fixomull sensor demonstrates high stretchability of min. 80%, a linear range up to 30% strain and reliable data acquisition up to 60% strain as well as a stable signal output for 20 subsequent stretch-release cycles to 30% strain.