The conformational evolution of elongated polymer solutions tailors the polarization of light-emission from organic nanofibers

TL;DR

This study investigates how the conformational evolution of elongated polymer solutions influences the polarization of light emitted from organic nanofibers, revealing nanoscale molecular organization and enabling tailored optical properties.

Contribution

It provides the first detailed analysis of nanoscale molecular orientation in electrospun fibers and links this to controllable light polarization properties.

Findings

Polymer chains stretch almost fully within 1 mm during electrospinning.

Nanoscale mapping shows a core-sheath structure with different molecular orientations.

Fiber properties, including light polarization, can be tailored through processing conditions.

Abstract

Polymer fibers are currently exploited in tremendously important technologies. Their innovative properties are mainly determined by the behavior of the polymer macromolecules under the elongation induced by external mechanical or electrostatic forces, characterizing the fiber drawing process. Although enhanced physical properties were observed in polymer fibers produced under strong stretching conditions, studies of the process-induced nanoscale organization of the polymer molecules are not available, and most of fiber properties are still obtained on an empirical basis. Here we reveal the orientational properties of semiflexible polymers in electrospun nanofibers, which allow the polarization properties of active fibers to be finely controlled. Modeling and simulations of the conformational evolution of the polymer chains during electrostatic elongation of semidilute solutions demonstrate that the molecules stretch almost fully within less than 1 mm from jet start, increasing polymer axial orientation at the jet center. The nanoscale mapping of the local dichroism of individual fibers by polarized near-field optical microscopy unveils for the first time the presence of an internal spatial variation of the molecular order, namely the presence of a core with axially aligned molecules and a sheath with almost radially oriented molecules. These results allow important and specific fiber properties to be manipulated and tailored, as here demonstrated for the polarization of emitted light.