A flexible piezoresistive pressure sensor based on PVA/GO/carboxylated carbon nanotube composite films

Flexible piezoresistive pressure sensors hold great promise for wearable health monitoring, motion recognition, and human-machine interaction. However, achieving high sensitivity, a broad pressure-response range, and long-term operational stability in composite-film-based devices remains challenging. Herein, we report a flexible piezoresistive pressure sensor based on a poly(vinyl alcohol) (PVA)/graphene oxide (GO)/carboxyl-functionalized carbon nanotube (COOH-CNT) composite film. The sensing film was fabricated by blade coating a homogeneous PVA/GO/COOH-CNT aqueous ink, followed by thermal drying at 60 ^\circ C for 24 h, and the device was assembled into a sandwich structure using Pt/PI electrodes. The composite film exhibited a continuous layered morphology, in which GO sheets provided a lamellar framework and COOH-CNTs acted as conductive bridges for pressure-induced resistance modulation. The sensor exhibited approximately linear current-voltage characteristics over the voltage range from -2 V to 2 V under applied pressures ranging from 0 to 88.4 kPa, with coefficients of determination (R^2 ) ranging from 0.98527 to 0.99289. The normalized current response exhibited three sensitivity regimes, with sensitivities of 152.1 kPa^-1, 39.7 kPa^-1, and 14.5 kPa^-1 over the pressure ranges of 44.2 Pa-8.49 kPa, 8.49-84.07 kPa, and 84.07-309.73 kPa, respectively. The device achieved a low detection limit of 44.2 Pa, a broad pressure-response capability up to 397.89 kPa, and response/recovery times of 333 ms and 267 ms, respectively, determined using the 90% signal-change criterion. Moreover, stable output was maintained over more than 5000 loading-unloading cycles at approximately 4.42 kPa. Wearable demonstrations, including wrist-pulse monitoring, finger and wrist bending detection, and respiration monitoring, confirmed the capability of the sensor to detect both subtle physiological signals and large-amplitude human motions. This work provides a facile strategy for developing flexible composite-film pressure sensors for wearable sensing applications.