Airbrushed PVDF-TrFE Fibrous Sensors for E-Textiles

The low-temperature processing, inherent flexibility, and biocompatibility of piezoelectric polymers such as poly(vinylidene fluoride) (PVDF)-based materials enable the creation of soft wearable sensors, energy harvesters, and actuators. Of the various processing techniques, electrospinning is the most widely adopted process to form PVDF nanofiber scaffolds with enhanced piezoelectric properties such that they do not require further post-processing such as mechanical drawing, electrical poling, or thermal annealing. However, electrospinning requires long periods of time to form sufficiently thick PVDF nanofiber scaffolds and requires extremely high voltages to form scaffolds with enhanced piezoelectric properties, which limits the number of usable substrates, thus restricting the integration and use of electrospun PVDF scaffolds into wearable textile platforms. In this work, we propose a facile processing technique to airbrush PVDF-trifluoroethylene (TrFE) nanofiber scaffolds directly onto textile substrates. We tune the polymer concentration (4, 6, and 8 wt %) and the spray distance (5, 12.5, and 20 cm) to understand their effects on the morphology and crystal structure of the fibrous scaffolds. The characterization results show that increasing the polymer wt % encourages the formation of fibrous morphologies and a beta-phase crystal structure. We then demonstrate how the airbrushed PVDF-TrFE scaffolds can be easily integrated onto conductive inkjet-printed nonwoven textile substrates to form airbrushed piezoelectric textile devices (APTDs). The APTDs exhibit maximum open-circuit voltages of 667.1 +/- 162.1 mV under tapping and 276.9 +/- 59.0 mV under bending deformations. The APTDs also show an areal power density of 0.04 mu W/cm(2), which is 40X times higher compared to previously reported airbrushed PVDF scaffolds. Lastly, we sew APTDs into wearable textile platforms to create fully textile-integrated devices with applications in sensing a basketball shooting form.