Abstract
Polyvinylidene fluoride (PVDF) shows piezoelectricity related to its β-phase content and mechanical and electrical properties influenced by its morphology and crystallinity. Electrospinning (ES) can produce ultrafine and well-aligned PVDF nanofibers. In this study, the effects of the presence of carbon nanotubes (CNT) and optimized ES parameters on the crystal structures and piezoelectric properties of aligned PVDF/CNT nanofibrous membranes were examined. The optimal β content and piezoelectric coefficient (d33) of the aligned electrospun PVDF reached 88% and 27.4 pC/N; CNT addition increased the β-phase content to 89% and d33 to 31.3 pC/N. The output voltages of piezoelectric units with aligned electrospun PVDF/CNT membranes increased linearly with applied loading and showed good stability during cyclic dynamic compression and tension. The sensitivities of the piezoelectric units with the membranes under dynamic compression and tension were 2.26 mV/N and 4.29 mV/%, respectively. In bending tests, the output voltage increased nonlinearly with bending angle because complicated forces were involved. The output of the aligned membrane-based piezoelectric unit with CNT was 1.89 V at the bending angle of 100°. The high electric outputs indicate that the aligned electrospun PVDF/CNT membranes are potentially effective for flexible wearable sensor application with high sensitivity.
Highlights
With different demands from many consumers and advancing technology, smart textiles and portable electronic devices that sense human motion and environmental changes have become important research topics
The results showed that mechanical stretching could induce polyvinylidene fluoride (PVDF) crystal arrangement in the polarization structure (β phase), and that the mechanical stretching and electrical poling provided simultaneously in ES could further polarize the crystal structure into the β phase
It is evident that individual carbon nanotubes (CNT) are well dispersed in the PVDF nanofibers
Summary
With different demands from many consumers and advancing technology, smart textiles and portable electronic devices that sense human motion and environmental changes have become important research topics. Electrospun fibrous membranes collected on a fixed collector screen are randomly oriented [19] Wang and his co-workers used a rotating drum collector in ES to produce PVDF nanofibrous membranes [20]. Under the applied loading frequency of 7 Hz, the generated average peak voltage output value of the prepared piezoelectric unit was 76 mV Another aligned electrospun PVDF nanofiber mat was incorporated into a piezoelectric unit by Yu et al [23]. In the applied gas pressure range between 0.145 MPa and 0.165 MPa, the piezoelectric unit exhibited a sensitivity of 178 mV/kPa. In the aforementioned research on the piezoelectric performance of electrospun PVDF fibrous membranes, the application directions of mechanical forces to the PVDF samples were similar.
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