Small Angle Neutron Scattering Studies of Native and Chemically Modified Phytoglycogen Nanoparticles
Phytoglycogen is a highly branched polymer of glucose produced as soft, compact nanoparticles by sweet corn. Properties such as softness, porosity, and mechanical integrity, combined with nontoxicity and biodegradability, make phytoglycogen nanoparticles ideal for applications involving the human body. We used small angle neutron scattering (SANS) to study the structure, hydration and interaction of these nanoparticles. SANS measurements on dilute dispersions of highly purified, native phytoglycogen nanoparticles revealed that the particles are well described by the core-chain model in which the core of radius 21.0 nm is decorated by linear, “hairy” chains. SANS measurements of concentrated dispersions of native particles were consistent with a hard sphere model using the Percus-Yevick approximation, allowing the determination of the concentration dependence of the interparticle spacing. Hydrophobic modification of the particles with octenyl succinic anhydride (OSA) using a high degree of substitution resulted in the observation of a distinctive high-q scattering feature that we associated with the hydrophobic collapse of the hairy chains to form “seeds” on the outer surface of the particles within the context of the raspberry particle geometry. This SANS measurement of OSA-modified particles allowed the determination of the average length and packing density of the hairy chains on the native particles. SANS measurements of concentrated dispersions of OSA-modified particles revealed complex interparticle interactions due to the soft, sticky and charged nature of the OSA-modified particles. Hydrolysis of the particles using either hot acid or the amyloglucosidase enzyme resulted in smaller particles, increased polydispersity and increased hydration water, with interparticle interactions similar to those for the native particles. Collectively, the SANS results presented in this thesis provide new, unique, fundamental information on the structure, hydration and interactions of native and chemically modified phytoglycogen nanoparticles, establishing a quantitative basis for the development of new applications of this promising sustainable nanotechnology.