MoS₂ Nanosheet-Coated Carbon Fibers as Strain Sensors in Epoxy Composites

Recent decades have witnessed the massive growth of interest in two-dimensional (2D) nanomaterials. Molybdenum disulfide (MoS2) is one of the most attractive members of the 2D nanomaterial family, as it is semiconducting with a tunable band gap. Previous studies on the use of graphene as a strain sensor show the potential of 2D materials in composite-related applications. Compared with graphene, monolayer MoS2 has an intensive photoluminescence (PL) peak, which shows a large strain-induced shift, making it a preferential candidate as a strain indicator. In this study, we coated MoS2 grown by chemical vapor deposition (CVD) onto the surface of individual carbon fibers to act as strain indicators in a fiber/epoxy model composite, based on the strain-induced PL peak shift. It is demonstrated that the strain sensing ability of the coated MoS2 is highly reproducible during more than 10 cycles of deformation to ∼0.4% tensile strain without significant interfacial damage. The local fiber strain can be detected by the coated MoS2 under deformations up to ∼0.8% matrix strain, which is higher than that of CVD graphene reported previously. In addition, strain reporting along a coated fiber in the model composite can be achieved, from which the strain distribution along the fiber and the stress transfer at the interface can be investigated. This study shows the potential of MoS2 enabled by photoluminescence spectroscopy serving as a viable nanoscale strain sensor, which can be employed in fiber-reinforced composites to monitor local strain over a structure on the microscale.