Stress-induced structural changes in electrospun polyvinylidene difluoride nanofibers collected using a modified rotating disk

By attaching separate, parallel electrodes onto a rotating disk collector, well aligned electrospun polyvinylidene difluoride (PVDF), PVDF/carbon nanotube nanocomposite and vinylidene fluoride-trifluoroethylene copolymer nanofibers are directly deposited onto flat substrates forming relatively large, uniform and compact fibrous thin films. The attachments alter the electric-field distribution on the rotating disk, which fosters the fanning of the nanofibers, while the electric field between the separate electrodes and the mechanical force exerted by the rotational disk facilitate the alignment. X-ray diffraction and infrared spectroscopic studies show that the specific environment and force fields created on the modified rotating disk cause the electrospun fibers being effectively stretched to form highly oriented β-form crystallites with slightly reduced inter-chain distance. They also lead to slight increases in crystallinity and crystal size. A mechanism is proposed to account for the structural alteration induced by the modified rotating disk collector. Ferroelectricity of the aligned electrospun PVDF fibrous thin films is also demonstrated.