Synthesis and applications of conductive electrospun polymer fibers

Abstract

Electrospinning is a convenient and versatile method used for the production of high aspect-ratio nanostructures. This is one of the most widely adopted techniques to produce fibers with diameters in the nanometer to a few microns range. The synthesized fiber mats are extremely light-weight, have high porosity, and high specific surface area-to-volume ratio. It is a very simple, scalable, and cost-effective technique to synthesize nanomaterials with outstanding physical and chemical properties. These electrospun fiber mats have been used in a wide variety of applications spanning from healthcare and biomedical engineering to electronics and energy harvesting and storage. Moreover, high conductivity makes electrospun polymer fibers promising candidates for such applications.

All the synthesized fibers were subjected to thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to study the thermal properties of these novel composites. The physical characterization of all the electrospun fibers prepared in the current work was evaluated using scanning electron microscopy (SEM), x-ray diffraction (XRD), ultraviolet-visible (UV-VIS) spectroscopy and Fourier-transform infrared spectroscopy (FTIR).

Secondary dopants incorporated into polyaniline have generally been limited to solutions and films of the polymer so far. In this work, we study novel, non-toxic secondary dopants of polyaniline that can be used to electrospin PANI-PEO fibers with high electrical conductivity. This study highlights the different parameters that need to be considered for electrospinning PANI-PEO with secondary dopants in order to achieve high conductivity. The roles that pKa values, dipole moments, and electron donating propensity of these dopants in changing the electrical properties of PANI-PEO fibers have been investigated in this work. Chloroxylenol dopant ended up being the best of the set we tested.

Chloroxylenol, an established anti-microbial agent was studied as a new secondary dopant of PANI to make the surface of the polyaniline fiber positively charged. In this work, the effect of positively charged polymer fiber mats as antibacterial gauze is studied using electrospun poly(ε-caprolactone) and polyaniline nanofibers. Both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli are used to investigate the antibacterial activity of the positively charged and uncharged polymer surfaces. The results show that the polyaniline surface can inhibit the growth of both bacteria even when chloroxylenol is used below its minimum inhibitory concentration. This study provides new insights allowing the better understanding of dopant-based, intrinsically conducting polymer surfaces for use as antibacterial fiber mats.

A novel corrugated, rotating electrospinning mandrel was designed successfully to facilitate synthesizing polymer fibers from high boiling point solutions which has been a challenge to the field. The mass transfer was studied and analyzed to optimize the mandrel design. Using this mandrel collector, conducting polyaniline fibers with high conductivity values and high charge storage capacity were successfully synthesized. Intrinsically conductive polymers (ICPs), such as polyaniline (PANI), show higher conductivities with the use of secondary dopants like m-cresol. However, due to the low volatility of most secondary dopants, it has not been possible to electrospin secondary doped ICP fibers. In this work, the concept of secondary doping has been applied for the first time to electrospun fibers. Using a novel design for rotating drum electrospinning, fibers were efficiently and reliably produced from a mixture of low and high volatility solvents. The conductivity of electrospun PANI-PEO fibers prepared was 1.73 S/cm, two-orders of magnitude higher than average value reported in the literature. These conductive fibers were tested as electrodes for supercapacitors and were shown to have a specific capacitance as high as 3121 F/g at 0.1 A/g, the highest value reported, thus far, for PANI-PEO electrospun fibers.