Small-angle X-ray and light scattering analysis of multi-layered Curdlan gels prepared by a diffusion method

Area of Science:

• Biopolymer science
• Materials science
• Physical chemistry

Background:

• Curdlan, a microbial polysaccharide, forms complex multi-layered gels with varying turbidity when dialyzed against calcium ions (Ca2+).
• Understanding the microstructure of these diffusion-set gels is crucial for controlling their properties.

Purpose of the Study:

• To elucidate the detailed microstructure of each layer in diffusion-set Curdlan gels.
• To correlate the observed microstructures with the gelation process involving pH and Ca2+ gradients.

Main Methods:

• Small-angle X-ray scattering (SAXS) to analyze nanoscale structures and chain conformations.
• Small-angle light scattering (SALS) to characterize micrometer-scale inhomogeneities.
• Analysis of 2D SAXS patterns to determine structural anisotropy.

Main Results:

• Curdlan chains adopt a helical conformation within the gel, forming fibrils and fibril aggregates.
• Gelation in the outer layer is driven by Ca2+-cross-linked fibril networks, while the inner layer involves aggregation of fibrils during neutralization.
• Fibrils exhibit circumferential orientation in the outer gel region and random orientation in the inner region.
• Inhomogeneous structures in turbid layers have characteristic lengths on the micrometer scale.

Conclusions:

• The distinct layered structure of diffusion-set Curdlan gels arises from spatial variations in pH and Ca2+ during gelation.
• SAXS and SALS provide complementary insights into the hierarchical structure of Curdlan gels, from molecular conformation to macroscopic inhomogeneities.
• The findings offer a deeper understanding of polysaccharide gel formation and structure-property relationships.