Cr3+/COO-Complexation Induced Aggregation of Gelatin in Dilute Solution

Abstract

The Cr3+/COO- complexation induced aggregation of linear gelatin chains in aqueous solutions under different conditions, such as the Cr3+ and gelatin concentrations, was investigated by a combination of static and dynamic laser light scattering (LLS). The results reveal a competition between the intrachain and interchain complexation. For a given gelatin concentration, there exists a “critical” Cr3+ concentration at which the interchain complexation became dominant. The intensity I(q) of the light scattered from the resultant aggregates was scaled to the scattering vector q as I(q) ∝ q-dq with dq = 1.61−1.84, suggesting that the aggregation was a diffusion-limited process. The variation of the Cr3+ concentration had less influence on the structure of the resultant aggregates. On the other hand, the decrease of the gelatin concentration led to an increase of dq from 1.61 to 2.04, indicating that the aggregation changed from a diffusion-limited process to a reaction-limited one. Precipitation is independent of the size of the aggregates but closely related to the gelatin concentration as well as the Cr3+/gelatin molar ratio. Two-dimensional AFM topographs of the aggregates revealed a clear growing fractal, supporting the results observed by LLS.