Effects of functionalized latex particles and anionic surfactants on the flow behavior of aqueous gelatin dispersions

The flow behavior of aqueous gelatin dispersions containing latex particles with different surface characteristics is studied as a function of the concentration of anionic surfactants. The work describes the nature and strength of interactions occurring in the system. The study of the effects of individual components may help to gain information on the flow behavior of commercial photographic color coupler dispersions. Due to interactions with the gelatin, the flow behavior of a dispersion of latex particles in 4.6% (w/w) aqueous gelatin solution depends strongly on charge and surface characteristics of the particles. For hard particles with nonionic hydrophilic shells, the flow behavior can be described by the theory of hard spheres. If anionic surfactants such as sodium i-dodecylbenzenesulfonate (DBS) or sodium di-sec-butylnaphthalenesulfonate (BXG) are added, the rheological behavior is mainly determined by the interactions between the gelatin and the surfactants in the continuous phase. If soft particles with ionic shells are dispersed in the aqueous gelatin, the viscosity is more strongly increased than predicted by the hard sphere model. Upon further addition of a surfactant, the primarily pseudoplastic flow behavior becomes more and more Newtonian, presumably due to depletion of originally surface-adsorbed gelatin molecules. The stabilization of the latex is changed from steric to electrostatic. If large amounts of surfactant are added, depletion flocculation is most likely to occur. A model of the gelatin-latex-surfactant interactions is presented which takes into account the surface characteristics of the particles. (C) 1997 Academic Press.