Modeling and characterization of enhanced piezoelectric PVDF-TrFE/CoFe2O4 nanocomposites

In this study, we combined experimental Piezoresponse Force Microscopy (PFM) analysis with an empirically corrected Furukawa model to predict the piezoelectric behavior of Poly(Vinylidene Fluoride-co-Trifluoroethylene) (PVDF-TrFE) films functionalized with CoFe₂O₄ (CFO) Magnetic Nanoparticles (MNPs). According to our empirical model, the piezoelectric response observed from PFM analysis on the PVDF-TrFE/CFO films was mainly influenced by the interaction between the CFO MNPs and the polymer active β phase of the polymer, providing a high piezoelectric coefficient d₃₃ (~ 6.5 pm/V) at a low CFO concentration of 5 wt%. Experimental observation of the morphological formation of the polar β domains and their phase dependence from the CFO MNPs amounts have been investigated by means of Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Fourier Transform Infrared (FT-IR) spectroscopy analysis. Also, the local magnetic response of the PVDF-TrFE/CFO film at 5 wt% was investigated through Magnetic Force Microscopy (MFM) with a controlled magnetized tip. DC magnetic poling of the PVDF-TrFE/CFO film at 5 wt% resulted in a significant increase in the d₃₃ (~ 34 pm/V) under an applied external magnetic field of ~ 50 mT. A theoretical model of chain aggregate-like structure formation in magnetizable polymer-based nanocomposites was employed to explain the effect of CFO MNP chain unification on the local piezoelectric strain response of PVDF-TrFE/CFO films under low magnetic fields. This finding provide further insight into the implementation of flexible PVDF-TrFE/CFO thin nanocomposites with tailored piezoelectric performance, enhancing their efficiency in energy harvesting and advancing the development of next-generation piezoelectric devices.