Morphologies, structures and properties of electrospun poly(vinylidene difluoride)-based materials

Abstract

Electrospinning is a technique that can be used to produce nanofibers, and it is discovered that it is able to enhance the β-phase of poly(vinylidene difluoride), PVDF. Owing to its highest polarization per unit cell, the β-phase of PVDF exhibits the maximum electroactive properties, i.e., ferro-, pyro- and piezo-electric properties, in comparison with other phases of PVDF. Although researches have shown that the β-phase of PVDF can be improved by (1) alteration of the chemical structure, (2) usage of additives, (3) application of a stretching force and (4) the use of high temperature and pressure treatments, the synergistic effects among (2), (3) and (4) on polymorphism behaviors and electro-active of PVDF have not been studied. Thus, this work was undertaken to study polymorphism behaviors, morphologies and electro-active properties of electrospun poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) nanofibers and P(VDF-HFP)/carbon nanotube (CNT) composite nanofibers, which experienced high extensional forces in the electrospinning and collection processes, as well as high temperature and pressure treatments in supercritical carbon dioxide (SCCO2). Firstly, a modified rotating disk collector is used in electrospinning to provide stronger stretching force to the electrospun P(VDF-HFP) nanofibers. By attaching seperate, parallel electrodes onto a rotating disk collector, well aligned nanofibers of P(VDF-HFP)) and P(VDF-HFP)/CNT nanocomposites can be directly deposited onto flat substrates forming uniform and compact nanofibrous mats. The attachment alters the electric-field distribution on the rotating disk while providing an additional stretching force during the fanning of the fibers. This additional stretching force exerted by the modified rotating disk prevents the relaxation of the polymer chains during solvent evaporation, and hence results in the formation of extended-chain β-chain crystallites with a slightly reduced inter-chain distance, as evidenced by wide angle X-ray diffraction (WAXD) patterns and Fourier transform infrared (FTIR) spectra of the samples.