Highly stretchable strain sensors based on Marangoni self-assemblies of graphene and its hybrids with other 2D materials.

Graphene and other two-dimensional materials (2DMs) have been shown to be promising candidates for the development of flexible and highly-sensitive strain sensors. However, the successful implementation of 2DMs in practical applications is slowed down by complex processing and still low sensitivity. Here, we report on a novel development of strain sensors based on Marangoni self-assemblies of graphene and of its hybrids with other 2DMs that can both withstand very large deformation and exhibit highly sensitive piezoresistive behaviour. By exploiting the Marangoni effect, reference films of self-assembled reduced graphene oxide (RGO) are first optimized, and the electromechanical behaviour has been assessed after deposition onto different elastomers demonstrating the potential of producing strain sensors suitable for different fields of application. Hybrid networks have been then prepared by adding hexagonal boron nitride (hBN) and fluorinated graphene (FGr) to the RGO dispersion. The hybrid integration of 2D materials is demonstrated to become a potential solution to increase substantially the sensitivity of the produced resistive strain sensors without compromising the mechanical integrity of the film. In fact, for large quasi-static deformations, a range of gauge factor values up to 2000 were demonstrated, while retaining a stable performance under cyclic deformations.