Rheo-Impedance Behavior during the Gelation Process of a Gelatin Solution
In this report, the internal structural evolution of gelatin during cooling was evaluated in real time using the Rheo-Impedance technique, which enables simultaneous acquisition of rheological and electrical impedance data.
Gelatin aqueous solutions exhibit a reversible sol-gel transition upon heating and cooling. By varying the cooling rate, we found that the sharp increase in the elastic modulus shifted toward lower temperatures and shorter times as the cooling rate increased. The apparent plateau storage modulus (G’p) at the convergence of gelation was higher under slower cooling conditions. The impedance magnitude |Z| increased as the temperature decreased, and the internal resistance R1 obtained from the equivalent circuit analysis exponentially increased from the sol state to the vicinity of the sol-gel transition. Furthermore, R1 showed a proportional relationship with G’p, suggesting that R1 reflects the increase in molecular weight and network density associated with crosslinking. Therefore, the Rheo-Impedance is an effective method for quantitatively evaluating the dynamic transition from sol to gel, which is difficult to capture by only conventional viscoelastic measurements.
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