Gel point determination of gelatin hydrogels by dynamic light scattering and rheological measurements

The sol-gel transition of gelatin aqueous solutions has been investigated in terms of time-resolved dynamic light scattering (DLS) and rheological measurements during the cooling process. A drastic increase in the scattering intensity, ergodic-nonergodic transition, and a power-law behavior in the scattering intensity-time correlation function were observed at the gelation temperature $T_{\mathrm{gel}}$. Thus obtained “microscopic” $T_{\mathrm{gel}}$ was confirmed to be in good agreement with a “macroscopic” $T_{\mathrm{gel}}$ obtained by rheological measurements irrespective of gelatin concentration $C$. The fractal exponent $D_{\mathrm{p}}$ evaluated by DLS was found to be $q$ and $C$ independent and was also in good agreement with that obtained by rheology $\left(n\right)$, i.e., $D_{\mathrm{p}}\cong n\cong 0.73$, where $q$ is the magnitude of the scattering vector.