Aqueous Subphase-Directed Crystallization of β-Phase P(VDF-TrFE)/TiO ₂ Nanocomposite Films without Thermal or Mechanical Treatment for High-Performance Piezoelectric Energy Harvesting

With the rapid development of portable and wearable devices, there is growing interest in long-lasting and efficient power supplies. A flexible piezoelectric nanocomposite Langmuir–Schaefer (LS) film was fabricated to convert mechanical energy into usable electrical energy for energy-storage devices. This study investigates the synthesis and characterization of P(VDF-TrFE)/TiO2 nanocomposite LS films, with a focus on their morphological, structural, and piezoelectric properties. The films were prepared by spreading titanium dioxide nanoparticles (TiO2-NPs) of varying concentrations (2–40 wt %) onto a water subphase and then compressing them to form well-ordered monolayers. Through a detailed investigation of the Langmuir surface pressure–area (π–A) isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy, it was demonstrated that TiO2-NPs effectively promote formation of the β-phase in P(VDF-TrFE) films. The water subphase played a critical role in aligning the polymer chains and enhancing crystallization of the β-phase content 97%, without relying on traditional techniques such as thermal annealing or mechanical stretching. The interaction between the hydrophilic TiO2-NPs and polar P(VDF-TrFE) chains facilitated β-phase nucleation through hydrogen-bonding and dipole–dipole interactions, leading to a highly ordered dipole alignment. The highest output voltage of 68 V and current of 8.6 μA were obtained at 2 wt % filler content and 5 mN/m for two LS films. The output voltage increased upon bending the strain rate from 1 to 2.5 Hz. Additionally, the devices showed promising energy-storage capabilities, with the 2 wt % TiO2 composite storing up to 723 μJ in a 5 μF capacitor. These findings highlight the importance of the filler concentration, subphase conditions, and nontraditional fabrication methods for the development of high-performance flexible piezoelectric nanogenerators and their use for high-performance flexible piezoelectric energy-harvesting applications.