The Interactions Between Gelatin and Surfactants — A Rheological Study

Abstract

Gelatin and surfactants are ubiquitous in photographic products. Addition of surfactants to gelatin solutions may have little effect or may lead to dramatic changes in physical properties. Here, a rheological study of gelatin solutions in the presence and absence of surfactant is reported. Simple viscometry-shear rate data is supplemented by investigations of the complex rheology using oscillation, stress relaxation, stress growth and pulse shearometry. The effects of ionic (AOT, SDS and CTAB) surfactants and nonionic (alkyl polyether) surfactants on the rheology of gelatin solutions are compared. Anionic surfactants, at con-centrations above the CMC (in gelatin), lead to a greater increase in viscosity than do cationic surfactants. Nonionic surfactants have little effect on the viscosity of gelatin solutions. All solutions exhibit similar complex rheology. At low frequencies (w < 1000 s^-1) the behaviour is dominated by the loss (viscous/liquid) rather than the storage elastic/solid) component. There is a characteristic relaxation time at 35-55ms and, for the elastic properties, there appears to be a relaxation time in the range 0.1- lms. Mechanisms for the above processes are dis-cussed.