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

Abstract

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.

Orientation and Partial Disentanglement in Individual Electrospun Fibers: Diameter Dependence and Correlation with Mechanical Properties

“…In that case, the ⟨P 2 ⟩ values were quantitatively correlated with the fraction of trans conformers associated with the formation of a mesophase made possible by the orientation of the chains. 40 These results highlight the reality of the distribution of structural characteristics for fibers of a given diameter and, thus, the requirement of probing large quantities of fibers for an accurate diameter−orientation correlation to emerge. It should be stressed that the large distribution of ⟨P 2 ⟩ values in Figure 2A is highly reminiscent of that observed for mechanical properties measured at the single fiber level, suggesting that they share the same origin in the chaotic nature of jet elongation in the whipping zone during the electrospinning process.…”

“…Nevertheless, acquiring four polarized spectra on micro-or nanoscale fibers is extremely time-consuming considering the numerous experiments that must be rejected based on previously described criteria. 40 Not respecting these stringent conditions could induce large errors in the ⟨P 2 ⟩ values of individual fibers. To circumvent this issue, a calibration curve enabling the quantification of ⟨P 2 ⟩ using a single polarized Raman spectrum was established using 35 fibers and validated by seven oriented films (see Figures S1 and S2 in the Supporting Information).…”

Structural Organization of Insulin Fibrils Based on Polarized Raman Spectroscopy: Evaluation of Existing Models

“…79 The procedure for determining the orientation of chemical groups based on polarized Raman spectroscopy has been previously reported. 35,80,81 Briefly, this method is based on acquiring four polarized Raman spectra (I ZZ , I ZX , I XX , and I XZ ) in the backscattering configuration 35 (see the Supporting Information).…”

IR Absorption, Raman Scattering, and IR-Vis Sum-Frequency Generation Spectroscopy as Quantitative Probes of Surface Structure

“…IR (28)(29)(30)(31)(32), Raman (33)(34)(35)(36)(37)(38)(39), second-harmonic generation (SHG) (40)(41)(42)(43)(44)(45), and SFG (18,(46)(47)(48)(49)(50)(51)(52)(53)(54)(55) spectroscopy have all been developed into quantitative techniques for structural determination using polarized light. Many studies have explored the surface specificity of SHG/SFG (18,19,45,(56)(57)(58), but there have been only a few reports that discuss the technique in comparison to IR and Raman approaches for the same molecules (43,(59)(60)(61)(62)(63).…”