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

Year: 2014

Authors: Camposeo A., Greenfeld I, Tantussi F., Moffa M., Fuso F., Allegrini M., Zussman E., Pisignano D.

Autors Affiliation: National Nanotechnology Laboratory of Istituto Nanoscienze-CNR, via Arnesano, I-73100 Lecce, Italy; Department of Mechanical Engineering, Technion−Israel Institute of Technology, Haifa 32000, Israel; Dipartimento di Fisica “Enrico Fermi” and CNISM, Universita  di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy; Istituto Nazionale di Ottica INO−CNR, Sezione di Pisa, I-56127 Pisa, Italy; Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Universita  del Salento, via Arnesano I-73100 Lecce, Italy

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.

Journal/Review: MACROMOLECULES

Volume: 47 (14)      Pages from: 4704  to: 4710

More Information: We gratefully acknowledge the financial support of the United States-Israel Binational Science Foundation (BSF Grant 2006061), the RBNI-Russell Berrie Nanotechnology Institute, and the Israel Science Foundation (ISF Grant 770/11). The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 306357 (ERC Starting Grant NANO-JETS). The authors also gratefully thank S. Pagliara for sample preparation, E. Caldi for assistance in the SNOM measurements, S. Girardo for imaging of the polymer jet, and V. Fasano for confocal images.
KeyWords: Electrospun Nanofibers; Molecular-orientation; Mechanical-properties; Conjugated Polymers; Fibers; Spectroscopy; Composites; Anisotropy; State
DOI: 10.1021/ma500390v

Citations: 30
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