Thermo-compression-aligned functional graphene showing anisotropic response to in-plane stretching and out-of-plane bending

Flexible and wearable sensors with high sensitivity are being expected for high-precision detection of subtle motions in human joints. In this study, we develop a graphene-based elastomer with tunable dielectric properties, which was further employed to construct a flexible capacitive sensor with highly anisotropic responses to the out-of-plane bending and in-plane stretching. To fabricate such a sensor, functional graphene derivatives are uniformly dispersed in a thermoplastic polyurethane (TPU) matrix and then aligned by a thermo-compression process. The uniform dispersion enables to elevate dielectric performance in composites leading to a high relative permittivity value of 97.3. In addition, adjacent graphene flakes are parallel to the hot plates due to the thermo-compression-induced alignment, thus behaving as microcapacitors to contribute to the sensitivity enhancement in the resulting sensors. Particularly, such sensors exhibit a sensitive response to the out-of-plane bending (30–180^o), but are insensitive to the in-plane stretching (0–40 N). We further demonstrate that this sensor has a potential application in the field of virtual typing output.