Deformation Mode-Sensitive Piezoelectric Hybrid Nanocomposite Films Based on Anionic Waterborne Polyurethane, Barium Titanate Nanoparticles, and Boron Nitride Nanosheets

We investigate the microstructure and deformation mode-sensitive piezoelectric performance of waterborne polyurethane (WPU)-based hybrid nanocomposite films reinforced with 0-dimensional barium titanate (BT) nanoparticles and 2-dimensional boron nitride (BN) nanosheets. To this end, anionic WPU-based hybrid nanocomposites, including 40 wt % hybrid fillers composed of different BT/BN contents (BN content of 0–10 wt %), are fabricated via a sequential process of aqueous dispersion casting, hot pressing, and electric poling. The BT nanoparticles are characterized as agglomerated in the WPU matrix, while BN nanosheets are randomly distributed. The dielectric constant and loss values are highest for the nanocomposite film with only 40 wt % BT loading, and they decrease with the increment of the relative BN content in 40 wt % hybrid fillers. Under the compression deformation mode, the piezoelectric outputs (voltage, current, and power) of the nanocomposite films decrease with the increment in the relative BN content of the hybrid fillers. On the other hand, under the bending deformation mode, the piezoelectric outputs increased with the increment in the BN loading in the hybrid fillers up to 7 wt %. This deformation mode-sensitive piezoelectric performance of the hybrid nanocomposite films is associated with the difference in dipole moment directions between BT nanoparticles and BN nanosheets. In addition, the WPU/BT/BN-based hybrid nanocomposite films exhibit piezoelectric sensing performance depending on the compressive stress (5–30 kPa) as well as the bending curvature radius (3–15 mm).