Local mechanical properties of electrospun fibers correlate to their internal nanostructure.
American Chemical Society
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The properties of polymeric nanofibers can be tailored and enhanced by properly managing the structure of the polymer molecules at the nanoscale. Although electrospun polymer fibers are increasingly exploited in many technological applications, their internal nanostructure, determining their improved physical properties, is still poorly investigated and understood. Here, we unravel the internal structure of electrospun functional nanofibers made by prototype conjugated polymers. The unique features of near-field optical measurements are exploited to investigate the nanoscale spatial variation of the polymer density, evidencing the presence of a dense internal core embedded in a less dense polymeric shell. Interestingly, nanoscale mapping the fiber Young's modulus demonstrates that the dense core is stiffer than the polymeric, less dense shell. These findings are rationalized by developing a theoretical model and simulations of the polymer molecular structural evolution during the electrospinning process. This model predicts that the stretching of the polymer network induces a contraction of the network toward the jet center with a local increase of the polymer density, as observed in the solid structure. The found complex internal structure opens an interesting perspective for improving and tailoring the molecular morphology and multifunctional electronic and optical properties of polymer fibers.
V. Fasano and G. Potente are acknowledged for confocal and SEM images, respectively. The authors also gratefully thank S. Girardo for high-speed imaging of the polymer jet and E. Caldi for assistance in the SNOM measurements. 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 306357 (ERC Starting Grant “NANO-JETS”).
This is the final version of the article. Available from the publisher via the DOI in this record.
Vol. 13, pp. 5056 - 5062
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