Effects of Graphene Morphology on Properties of Carbon Nanotube/Polyurethane Film Strain Sensors

The film flexible sensors can convert tiny changes in size or force into electrical signals. They are key components of intelligent devices and wearable devices, and are widely used in human-computer interaction, electronic skin, health monitoring, implantable diagnosis, and other fields. This kind of sensor is generally composed of polymer matrix and conductive components, while carbon nanotubes (CNT) and graphene (GN), as typical one-dimensional and two-dimensional conductive carbon nano-materials, respectively, have been used to build film flexible sensors. In order to explore the relationship between the GN size and thickness, and the performance of film sensors, the GN-CNT/PU composite film sensors were prepared by in situ polymerization of polyurethane (PU) in the presence of GN and CNT. A highly sensitive GN-CNT/PU flexible film sensor was prepared with a high gauge factor (GF) up to 13.15 in a strain range of 0–20%; an exceptionally low percolation threshold of GN is about 0.04 vol% when the CNT content is fixed at 0.2 vol%, which is below the percolation threshold of CNT/PU nanocomposites. The size of the GN layer affects the GFs of the flexible film sensors; a GN with a smaller size can achieve a greater GF. This study paves the way for the better application of different qualities of GN in flexible sensors.