Silk fibers have attracted tremendous practical interest, thanks to their excellent mechanical properties. It is essential to study the connection between their macromolecular structure and functional properties, to better understand these fibers.
Hierarchical models are available, and small angle / wide angle x-ray scattering (SAXS/WAXS) is a highly effective method for examining this type of sample. SAXS/WAXS allows the analysis of structural parameters such as crystallite size and orientation, which affect the strength of the silk.
Measurements and Results
The Xeuss 2.0 SAXS/WAXS system was used to measure a bundle of
B. mori cocoon silk fibers in simultaneous SAXS/WAXS mode. The SAXS range gives the morphological structure data in nanoscale (Figure 1).
Figure 1. 2D anisotropic SAXS pattern from B. mori cocoon silk fibers.
The high anisotropy observed can be explained by the distinct correlation lengths based on the fiber direction:
Equatorial direction d = 9.32 nm
Meridional direction d = 18.32 nm
These dimensions are inferred from the Porod illustration of the 1D curves acquired from the 2D pattern. Figure 2 shows a schematic view of the fiber with an illustration of the crystalline portion and characteristic dimensions.
In addition, azimuthally regrouped WAXS intensity is plotted as a function of the q-vector (Figure 3). Comparison of these results from Riekel et al.
1, obtained at ESRF, on B. mori cocoon silk, makes it possible to classify the crystalline peaks.
Figure 2. Schematic representation of a silk fiber.
Figure 3. 1D WAXS curve from B. mori cocoon silk fibers.
The silk structure and its mechanical properties are greatly influenced by the spinning method of the silk fiber itself. In-situ experiments of silk structure as a function of the speed drawings have already been carried out on synchrotron beamlines.
The ergonomics and versatility of the Xeuss 2.0 system enables air experiments with a large sample volume and instantaneous SAXS/WAXS measurements.
Riekel C. and al., J. Am. Chem. Soc. vol. 130, 2008, p.17070-17074.
Du N et al. Biophysical Journal, Volume 91, December 2006, 4528-4535.
This information has been sourced, reviewed and adapted from materials provided by Xenocs.
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