# PhD Thesis Defence: Effect of Chemical Modification on the Rheology of Aqueous Dispersions of Phytoglycogen Nanoparticles

## Location

Videoconference
For instructions to join please email: physgrad@uoguelph.ca by Monday, May 30, 2022

Hurmiz Shamana

## Abstract

​Phytoglycogen (PG) is a natural polysaccharide produced in the form of compact, 44 nm diameter nanoparticles (NPs) in the kernels of sweet corn. Its highly branched, dendritic structure and soft, compressible nature leads to interesting and useful properties that make the particles ideal as unique additives in personal care, nutrition, and biomedical formulations. To enhance the practical use of PG NPs towards these applications, it is often desirable to modify their properties. This talk will focus on the effects of three chemical modifications of PG NPs: acid hydrolysis of PG NPs, charge modification of PG NPs by the covalent attachment of positively charged glycidyltrimethylammonium chloride (GTAC) chemical groups to the particles and a hydrophobic modification of PG NPs by the covalent attachment of negatively charged octenyl succinic anhydride (OSA) chains to the particle surface. We have performed rheology measurements to investigate the effects of these chemical modifications on the flow properties and interactions between PG NPs in water, as a function of the effective volume fraction $\phi _{eff}$ of the particles, focusing on measurements of the relative zero-shear viscosity $\eta_r$. The rheology of acid hydrolyzed PG NPs was consistent with softer particles relative to native PG NPs, as indicated by a more gradual increase in $\eta_r$ with increasing $\phi_{eff}$ with a sudden transition from a faster-than-exponential to exponential dependence for $\phi_{eff}$ > 1. Dispersions of the charged GTAC-modified PG NPs were significantly more viscous than those of native PG NPs and showed a much steeper increase in $\eta_r$ with increasing $\phi_{eff}$. GTAC-PG NP dispersions were sensitive to salts and showed a significant reduction in $\eta_r$ with added NaCl. The behaviour of OSA-modified PG NPs was dependent on the degree of substitution (DS) of OSA: for low DS values, the rheology of OSA-modified PG NPs was dominated by electrostatic interactions and behaved analogously to that of GTAC-PG NPs. For higher DS values, hydrophobic interactions were more significant, and we observed evidence for clustering of the particles when NaCl was added to the dispersions. These results highlight the high degree of tunability of PG NPs and suggest promising new applications for the particles.

## Examination Committee

• Dr. Eric Poisson, Chair