Orientation and Structure of Single Electrospun Nanofibers of Poly(ethylene terephthalate) by Confocal Raman Spectroscopy

The ability to characterize individual electrospun fibers is essential in order to understand and control this complex process. In this paper, we demonstrate that confocal Raman microscopy is a powerful method to quantify molecular orientation and structure at the individual fiber level using poly(ethylene terephthalate) as a model system. Highly reproducible polarized spectra with an excellent signal-to-noise ratio were measured in 1 min or less for fibers with a diameter as little as 500 nm. The orientation of smaller fibers can also be probed using a calibration procedure. Our results reveal a very broad distribution of molecular orientation and structure within the samples: some individual fibers are completely isotropic and amorphous while others present a < P-2 > orientation parameter as large as 0.75. The development of this large orientation is accompanied by a gauche-to-trans structural conversion into the mesomorphous phase. Even the most highly oriented fibers only present a very small degree of crystallinity.