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 (30–180o), 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.
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We thank Dr. Su Shimei for support with dielectric measuring, and we gratefully acknowledge the financial support from the key research project plan of Higher Learning Institutions of Henan Province (17B430008), the National Natural Science Foundation of China (51573169 and 61704155) and the Startup Research Fund for Young teachers of Zhengzhou University (F0000907 and F0000992).
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Xu, B., Yang, H., Dai, K. et al. Thermo-compression-aligned functional graphene showing anisotropic response to in-plane stretching and out-of-plane bending. J Mater Sci 53, 6574–6585 (2018). https://doi.org/10.1007/s10853-018-2021-1