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Description
Phytoglycogen (PG) is a highly branched biopolymer that occurs naturally as compact, soft, hydrated and hairy nanoparticles with an underlying dendritic architecture. Collectively, these properties make PG a unique soft colloidal nanoparticle for fundamental studies that is also desirable for personal care, nutrition, and biomedical applications. The functionality of PG can be modified through covalent attachment of chemical groups such as octenyl succinic anhydride (OSA), a negatively charged, hydrophobic molecule. High degrees of substitution (DS) of OSA result in the hydrophobic collapse of OSA-modified chains on the surface of the PG particles [1]. In the present study, we vary the DS value and use rheology to measure the divergence of the zero-shear viscosity of aqueous dispersions of OSA-PG with increasing OSA-PG concentration. We find that the glass transition concentration, at which the relative viscosity is $10^{5}$, changes nonmonotonically with DS: it decreases rapidly with DS for low DS values and then increases more gradually with DS for high DS values. We attribute this nonmonotonic dependence on DS to the competing effects of electrostatics, which dominate at small DS, and hydrophobicity, which dominates at large DS.
[1] J. Simmons et al., Biomacromolecules 21, 4053 (2020).
| Keyword-1 | charged colloids |
|---|---|
| Keyword-2 | amphipathic nanoparticles |
| Keyword-3 | rheology |