Perceived color of undoped electrospun polyacrylonitrile nanofibers

Abstract

This work reveals influence of electrospinning of polyacrylonitrile-N,N-dimethylformamide solution of different concentrations on nanofiber web color parameters, molecular structure, and heat stability. It is found that fiber diameters depend on concentration through the power law relationship; however, the medium concentration-based web is characterized by a green-yellow hue, representative of the chromophore color; while, the solvent-rich and solvent-poor solution-based webs give rise to Stokes shifts and ultraviolet-blue emission bands, attributed to fluorescence. The chromophore structure, present in the neat powder, undergoes changes as a result of electrospinning reflected by the enamine-to-ketonitrile conversion and the fraction of C=N conjugation. Blue-shifting of the C=N conjugation is indicative of a reduction of the pi-electron system, which is coincident with the decreased color saturation value but observed only in the nanofibers prepared from the medium concentration solution. A decrease in the glass transition and an increase in cyclization temperatures also support these findings.