Mechanical and piezoelectric properties of surface modified (Na,K)NbO₃-based nanoparticle-embedded piezoelectric polymer composite nanofibers for flexible piezoelectric nanogenerators

The degree of transformation from mechanical to electrical energy by flexible piezoelectric nanogenerators (f-PNGs) to power wearable electronics can be significantly enhanced through the synergy between piezoelectric ceramic nanoparticles (PCNPs) and flexible piezoelectric polymers. In this study, we investigated the mechanical and piezoelectric properties of composite nanofibers (c-NFs) of lead-free (Na, K)(Nb, Sb)O₃-BaZnO₃-(Bi, K)ZrO₃ (NKNS-BZ-BKZ) PCNPs embedded in a poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) matrix. A significant reduction in the agglomerate size of the PCNPs and their enhanced interfacial adhesion with the P(VDF-TrFE) matrix were achieved through a tetradecylphosphonic acid (TDPA) surface treatment of the PCNPs. The uniform distribution of the embedded PCNPs made the web of c-NFs have a highly negative relative surface potential and a high effective modulus of approximately 170 MPa. Consequently, the f-PNG with the TDPA surface-treated PCNPs maintained an open-circuit voltage, a high maximum generated power, and an output voltage of approximately 12.2 V, 33.2 nW, and 1.25 V, respectively, despite being bent for 10,000 cycles at a bending radius (r) of 15 mm.