Fabrication and Performance Evaluation of Piezoelectric Strain Sensors Made from PVDF/MWNT Nanocomposites

In this study, we fabricated piezoelectric strain sensors from multi-walled carbon nanotubes (MWNTs) and PVDF nanocomposites, i.e., PVDF/MWNT for measuring dynamic strains. The influence of MWNT loading on the sensor performance was evaluated by changing the MWNT loading as 0.0wt%, 0.05wt%, 0.2wt%, and 0.3wt%. To increase MWNT dispersion in PDVF matrix, a mixing process by using a planetary stirring machine and sonication processing by using an ultrasonic mixer were firstly employed together to produce nanocomposite films. Then, these films were stretched under uniaxial loading and poled under 60MV/m to fabricate the strain sensors. Moreover, crystallinity of the PVDF/MWNT nanocomposites was analyzed by using X-ray diffraction (XRD) analysis, and the fractured surfaces of pre-stretched PVDF/MWNT nanocomposites were observed by using a polarized optical microscope (POM). The piezoelectricity and signal tracking capability of the PVDF/MWNT nanocomposites sensors in vibration were investigated. From experimental results, the piezoelectricity, i.e., the sensor output voltage of the PVDF/MWNT nanocomposites reaches to a maximum peak value at 0.05wt% MWNT loading, and then decreases with further more addition of MWNTs. The result of XRD intensity was consistent with the piezoelectric sensor output results of PVDF/MWNT nanocomposites. From POM observations, compared to that of pure PVDF, the spherulite’s size in the PVDF/MWNT nanocomposites becomes smaller and its number increases. Moreover, there should exist an optimum content of MWNTs, which can result in high piezoelectric properties of the nanocomposite strain sensors.