Effects of ionic liquid/water addition and electrospinning conditions on the crystal structures of poly(vinylidene fluoride) nanofibers

Abstract

We investigated the effects of ionic liquids (ILs) and water addition, as well as electrospinning (ES) conditions, on the crystal structure of poly(vinylidene fluoride) nanofiber mats. We used 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMI][TFSI]), which can form hydrogen bonds with a polar polymer, as an IL. A much smaller amount of IL addition (0.25 wt% against the whole solvent) was sufficient to promote β phase formation of PVDF nanofibers, as compared to the previously reported case of PVDF film formation. Additionally, the water addition showed a similar β phase formation effect, but the influence was lower than that for IL addition. As for the ES condition, we examined the effects of applied voltage and rotating collector speed. These ES conditions changed the appearance and the processability of the nanofiber mats; however, they did not have much influence on the crystal structure. Moreover, we examined the piezoelectric properties; the piezoelectric output voltage decreased as the IL concentration increased, but this decrease was prevented by removing the remaining IL from the nanofiber mat sample.