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

Wearable textiles with integrated multimodal sensorshave numeroususes in the healthcare, entertainment, fitness, and fashion industries.However, the majority of reported sensors use different measurementmethods to measure different stimuli, i.e., strain, pressure, andtemperature. Further, they lack repeatability and stretchability formultimodal sensing. We have solved these issues by fabricating hybridpiezoelectric-capacitive sensors based on the PVDF-PU blend.Though PVDF, being a piezoelectric polymer, can be used as a dielectriclayer in a capacitive sensor, it shows a poor piezoelectric coefficientand is mechanically unstable to cyclic deformations. To overcome thisproblem, we have used a specific blend of PU with PVDF, which hasboth high stretchability and piezoelectric coefficient. PVDF79PU21 (with 21% PU) nanofiber capacitive sensors showeda multimodal response with an excellent sensitivity of 0.3 kPa(-1) for up to 8 kPa pressure stimuli, a good gauge factorranging between 0.5 and 0.75 for 0-40% cyclic strain, and highsensitivities of 0.8 and 2% degrees C-1 for 30-60and 60-100 degrees C, respectively. They could be used for measuringthe human body temperature in the range of 37-40 degrees C witha sensitivity of 0.9% degrees C-1. The prototypesof PVDF79PU21 nanofiber-based capacitive sensorswere attached to different body parts to measure extension and flexionmovements with high sensitivity, which showed its great potentialas a wearable sensor.