Fabrication of poly (vinylidene fluoride) films by ultrasonic spray coating; uniformity and piezoelectric properties

Piezoelectric Poly (vinylidene fluoride) (PVDF) films with high flexibility are a suitable and promising replacement for rigid ceramic piezoelectric materials. However, for this purpose, enhancing piezoelectric properties and adopting an industrial fabrication method are of great importance. In this study, 5–9 µm thick PVDF films were fabricated by a nozzle-less ultrasonic spray coating (USC) system, followed by an annealing process at 100 °C. By applying proper spraying parameters, we could obtain highly uniform films with large d33 values (48 pm/V) and 56% crystallinity. Results show that the uniformity of the films plays an important role in the final piezoelectric properties. Thus, ultrasonic spray coating method can be used for fabrication of large-scale piezoelectric films with no need for poling or stretching processes

From synthesis to application: High-quality flexible piezoelectric sensors fabricated from tetragonal BaTiO3/ P(VDF-TrFE) composites:High-quality flexible piezoelectric sensors fabricated from tetragonal BaTiO₃/ P(VDF-TrFE) composites

In this work, a simple process for fabrication of piezoelectric BaTiO3 /P(VDFTrFE) composites from synthesis to its application as a wearable piezoelectric sensor is presented. Addition of 10 wt% synthesized tetragonal BaTiO3 particles (200 nm in diameter) enhanced the mechanical and piezoelectric properties of P(VDF-TrFE) better than commercial cubic phase particles (&lt;100 nm in diameter). Although P(VDF-TrFE) and tetragonal BaTiO3 have opposite piezoelectric coefficients, BaTiO3 improved the performance of the final piezoelectric sensor by modifying the distribution of stress in the P(VDF-TrFE) matrix, reducing the viscosity, and causing the mechanical reinforcement of the composite films. This requires the uniform distribution of particles in the polymer matrix, which was succeeded by prior surface modification of the particles. Inverse piezoelectric properties of BaTiO3 /P(VDF-TrFE) composites were enhanced by obtaining a higher polarization (Pr = 6.18 µC/cm2) and dielectric constant value (εr = 30.3) compared to pure P(VDF-TrFE)(Pr = 4.23 µC/cm2, εr = 8.8). Furthermore, the ferroelectric and switching behavior in the composites happened at lower electric fields. With respect to direct piezoelectric properties, the voltage coefficient of this composite is 30% higher than the pure P(VDF-TrFE). By fabricating simple wearable piezoelectric sensors for finger joint movement detection, the composite device showed an enhancement in output voltage (2.1 times), power (4.6 times), and sensitivity (1.6 times) in comparison to the pure P(VDF-TrFE) sensor. The composite sensor with a sensitivity of 10.16 mV/N, is able to produce a maximum peak-to-peak output voltage of 400 mV by bending the finger without the need for any amplification or post-processing.</p