Effect of Electrostatic and Hydrophobic Interactions on the Rheology of Aqueous Dispersions of OSA-Modified Phytoglycogen Nanoparticles

Phytoglycogen (PG) is a natural polysaccharide produced in the form of compact, 44 nm diameter, electrically neutral nanoparticles in the kernels of sweet corn. Its highly branched, dendritic structure and hydrophilic nature leads to interesting and useful properties that make the particles ideal as unique additives in personal care, nutrition and biomedical formulations. The applications of PG can be extended by increasing the hydrophobicity of the particles. We have covalently attached charged, hydrophobic octenyl succinic anhydride (OSA) chains to the surface of PG at low (OSA_LDS) and high (OSA_HDS) degrees of substitution, and we have measured the rheology of dispersions of the particles in water. The results for OSA_LDS-modified PG dispersions were dominated by electrostatics: the dispersions developed solid-like rheology at a much smaller concentration (20% w/w) than that for native PG dispersions (32% w/w) but quickly liquified with added NaCl. For OSA_HDS-modified PG dispersions, hydrophobic interactions were more significant and we observed evidence for clustering of the particles with added NaCl. These results highlight the unique interplay between electrostatic and hydrophobic interactions of the particles and suggest new applications for OSA-modified PG.