Nano-structure of octenyl succinic anhydride modified starch micelle

The micelle nano-structures of octenyl succinic anhydride (OSA-starch) modified starches with different Mw (weight average molecular mass) in aqueous solution were studied. The micelle aggregates observation, maximum dimension (rmax) calculated from Pair Distance Distribution Function p(r) using General Indirect Fourier Transformation (GIFT) and radius of gyration (Rg) obtained from Guinier fitting of the small angle X-ray scattering data indicated the obvious geometric disparity of micelles originated from different OSA-starches. The micelle presented increased monodispersity in more concentrated aqueous solution. The OSA-starch molecules with the highest Mw formed the largest micelle. Hydrodynamic radius (Rh) via dynamic light scattering of the micelle with the highest Mw decreased in larger extent (from 80 nm to 46 nm), as well as more distinct change of Rg/Rh with increasing concentration, from which it could be deduced that the micelle conformation with higher Mw was more flexible and more sensitive to the interparticle electrostatic repulsion. Moreover, the most compact interior structure formed within the micelle with the highest Mw. The p(r) plots show typical profiles yielded from some oblate ellipsoid with a small subunit, long rod with a limited cross-section dimension and flattened prolate ellipsoid. It is anticipated that these nano-structures differences could be close related to stability and other properties of OSA-starch applied in oil-in-water system.

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► Micelle displayed more monodispersity and symmetry with higher OSA-starch/H2O ratio.
► OSA-starch with the highest Mw formed the largest but the most compact micelle.
► The largest micelle was more sensitive to the interparticle electrostatic repulsion.
► Micelle presented long rod, oblate and flattened prolate ellipsoid with diverse size.
► The nano-structure of micelle could largely determine the properties of OSA-starch.