Speaker
Description
Phytoglycogen (PG) is a glucose-based polysaccharide produced in the form of compact, monodisperse, electrically neutral nanoparticles in sweet corn kernels. Its highly branched, dendritic architecture leads to interesting and useful properties that make PG ideal as a unique additive in personal care, nutrition, and biomedical formulations. To tailor PG to specific applications, we can modify its properties. In the present study, we covalently attach cationic glycidyltrimethylammonium chloride (GTAC) groups to the PG particles, and we use rheology to measure the mechanical response of aqueous dispersions of GTAC-PG to steady and oscillatory shear. We measured dramatic increases in the relative zero-shear viscosity $𝜂_\text{r}$ with increasing effective volume fraction $𝜙_{\text{eff}}$, which is a characteristic feature of a soft colloidal glass. At low salt concentrations $𝐶_\text{NaCl}$, the divergence in $𝜂_\text{r}$ occurred at much smaller values of $𝜙_{\text{eff}}$ than for native PG due to electroviscous effects. With increasing $𝐶_\text{NaCl}$, the divergence in $𝜂_\text{r}$ approached that for native PG due to screening of the electrostatic interaction. By accounting for the electrostatic interaction by scaling the particle radius by the Debye screening length, the divergence in $𝜂_\text{r}$ revealed a significant increase in the particle stiffness with $𝐶_\text{NaCl}$, corresponding to an increase in the fragility of the glassy GTAC-PG dispersions. The oscillatory shear measurements on concentrated dispersions revealed a transition from a glassy to a liquid-like state with increasing $𝐶_\text{NaCl}$. Our measurements demonstrate the complex, tunable nature of the mechanical properties of aqueous dispersions of soft, charged PG nanoparticles.
| Keyword-1 | rheology |
|---|---|
| Keyword-2 | charged colloids |