Interfacial dynamics of a gelatin solution with surfactant

In terms of dynamic surface tension, the interfacial dynamics of gelation solutions with various surfactants are investigated by pendant bubble tensiometry. On the basis of local equilibrium assumption, the thermodynamics of dynamic surface tension is analyzed. The adsorption efficiency of gelatin is low compared to that of small surfactant. However, the surface activity of gelatin may be enhanced due to intrachain and interchain rearrangement at the interface, which results in long relaxation time signature. The interplay between adsorption efficiency and surface activity categorizes our experimental results into two types of dynamic behavior. For type I dynamics, the gelatin molecule is completely displaced from the interface, and the interfacial dynamics is dominated by that associated with surfactant. Nevertheless, the interaction of gelatin with surfactant in the bulk solution can alter the surfactant surface excess and hence the surface tension. For type II dynamics, the gelatin molecule is partially displaced from the surface, and the dynamics displays a long relaxation characteristic. The extent of surface tension decrement due to gelatin conformational change manifests the degree of gelatin displacement from the interface. Our conclusion is able to elucidate the peculiar dynamic surface tension of a solution of gelatin and PEG.