Unexpectedly high piezoelectricity of electrospun polyacrylonitrile nanofiber membranes

Highlights: • Polyacrylonitrile was electrospun into nanofibrous membranes. • Electrospun polyacrylonitrile membranes showed stronger piezoelectricity than electrospun polyvinylidene fluoride membranes. • The strong piezoelectricity of polyacrylonitrile nanofibers was mainly originated from the planar Sawtooth conformation. • Increasing fiber orientation led to larger piezoelectric outputs. -- Abstract: Polyvinylidene fluoride (PVDF) and its co-polymers are among the best piezoelectric polymer materials owing to the large piezoelectric coefficient and mechanical properties. Processing PVDF polymers into fibrous membranes through electrospinning can largely increase the piezoelectricity. In contrast, polyacrylonitrile (PAN), an amorphous polymer, is known to have a much lower piezoelectricity than PVDF. Herein, we report an unusually-high piezoelectric feature of electrospun PAN nanofiber membranes. When a small piece of PAN nanofiber nonwoven membrane (e.g. 5 cm²) was subjected to compressive impact, it can generate up to 2.0 V of voltage, the electrical outputs of which are even higher than that of PVDF nanofiber membranes at the same condition. Such unexpected piezoelectric properties were found to originate from the high content of planar Sawtooth PAN conformation within nanofibers. Electric charges in PAN nanofibers also contributed to the energy conversion. The energy conversion capability can be further enhanced by increasing fiber orientation within fibrous membrane. Also, the working area and thickness of nanofibrous membranes as well as impact conditions influenced piezoelectric outputs. The energy generated is usable and can power commercial LEDs. These unexpected discovery may inspire to develop novel piezoelectric materials and devices.