From synthesis to application: 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 (<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.