Hybrid Piezo-Capacitive Multimodal Sensors Based on Polyurethane–Poly(vinylidene fluoride) Nanofibers for Wearable E-Textiles

Wearable textiles with integrated multimodal sensors have numerous uses in the healthcare, entertainment, fitness, and fashion industries. However, the majority of reported sensors use different measurement methods to measure different stimuli, i.e., strain, pressure, and temperature. Further, they lack repeatability and stretchability for multimodal sensing. We have solved these issues by fabricating hybrid piezoelectric-capacitive sensors based on the PVDF–PU blend. Though PVDF, being a piezoelectric polymer, can be used as a dielectric layer in a capacitive sensor, it shows a poor piezoelectric coefficient and is mechanically unstable to cyclic deformations. To overcome this problem, we have used a specific blend of PU with PVDF, which has both high stretchability and piezoelectric coefficient. PVDF 79 PU 21 (with 21% PU) nanofiber capacitive sensors showed a multimodal response with an excellent sensitivity of 0.3 kPa –1 for up to 8 kPa pressure stimuli, a good gauge factor ranging between 0.5 and 0.75 for 0–40% cyclic strain, and high sensitivities of 0.8 and 2% °C –1 for 30–60 and 60–100 °C, respectively. They could be used for measuring the human body temperature in the range of 37–40 °C with a sensitivity of 0.9% °C –1 . The prototypes of PVDF 79 PU 21 nanofiber-based capacitive sensors were attached to different body parts to measure extension and flexion movements with high sensitivity, which showed its great potential as a wearable sensor.