Exploring a novel treatment method to enhance polar phases in electrospun PVDF nanofibers

Abstract

Poly (vinylidene fluoride) (PVDF) has drawn much attention due to the attractive properties such as piezo-, pyro-, and ferroelectricity, which are rarely exhibited in other polymers. The β phase has the largest spontaneous polarization (p) per unit cell of all polar phases and thus exhibits the highest piezo-, pyro and ferroelectric activities. This project aims to enhance β phase of PVDF through electrospinning and novel treatments.

Supercritical carbon dioxide¬ (scCO2) was utilized in the treatment of electrospun films and the effects of the experiment parameters such as temperature and pressure of scCO2 were examined through characterization. It showed that the β phase enhancement increased with increasing pressure. Additionally, the enhancement in β phase was also observed to increase with increasing treatment temperature when the temperature was below 80 ºC. This polymorphic behavior was possibly due to the nucleation of β form crystal with existing β phase as nucleus promoted by supercritical CO2.

Subsequently, multi-walled carbon nanotubes (MWCNTs) were added into PVDF solution with various weight percentages (PVDF/MWCNTs). It was found that the MWCNTs could promote β phase enhancement for PVDF via both electrospinning and spin-coating. Furthermore, supercritical CO2 treatment was utilized to the electrospun and spin-coated PVDF/ MWCNTs and found to further promote β phase enhancement.