CNT loaded PVDF-KNN nanocomposite films with enhanced piezoelectric properties

The emerging smart PVDF-based composites can compensate for the intrinsic property deficiencies in either of their components. The properties of the composite are determined by the properties of the constituents and its fabrication method. In this research, a lead-free piezoelectric ceramic, potassium sodium niobate (KNN), was used as the primary reinforcement, and MWCNTs were added to improve the electrical properties. Solution casting was used to prepare PVDF-KNN-CNT composite films. After phase and structure identification of composites using SEM, XRD, FTIR, and TGA methods, the dielectric, piezoelectric and ferroelectric properties of the products were investigated. The obtained results indicated a strong dependency of dielectric, piezoelectric, and ferroelectric properties of composites on KNN content. Samples with the highest KNN content rendered ε_r, d₃₃ and g₃₃ values of 156, 28 pC/N, and 20.32 mV m/N, respectively. Introducing a small amount of conductive CNT to primary PVDF-KNN composites can drastically affect the electrical properties by severely interfering in the charge distribution within the sample. While the dielectric constant was enhanced by increasing CNT content, both piezoelectric and ferroelectric properties showed their best behavior at a critical CNT loading. Beyond this limit, a percolation path formed, which is responsible for power consumption. At the optimum CNT amount, d₃₃ and g₃₃ reached 50 pC/N and 31.93 mV m/N, respectively. The presence of conducting CNTs gave rise to the formation of more round polarization curves with higher remnant polarization. The present findings give a prospective understanding of smart piezoelectric polymer-based composites that can be used as sensors and energy harvesters.