rheological behavior of the dispersion is still lacking. This The flow behavior of aqueous gelatin dispersions containing creates problems during the production process.
latex particles with different surface characteristics is studied as
The dispersions consist of hydrophobic color couplers a function of the concentration of anionic surfactants. The work which are usually dissolved in an oily solvent and are then describes the nature and strength of interactions occurring in the dispersed in an aqueous gelatin solution under high pressure.
system. The study of the effects of individual components may
The color coupler dispersion is mixed with the photographic help to gain information on the flow behavior of commercial photosilver halide dispersion and cast as a thin layer onto a polygraphic color coupler dispersions. Due to interactions with the mer support or paper. The film casting is a critical step in gelatin, the flow behavior of a dispersion of latex particles in 4.6% which problems such as schlieren formation, film rupture, (w/w) aqueous gelatin solution depends strongly on charge and surface characteristics of the particles. For hard particles with or imperfect wetting can occur. It is known that the wettabilnonionic hydrophilic shells, the flow behavior can be described by ity is strongly dependent on the nature of the surfactant (2, the theory of hard spheres. If anionic surfactants such as sodium 3). Since a high casting rate is desirable, the characterization i-dodecylbenzenesulfonate (DBS) or sodium di-sec-butylnaphthaof the shear rate dependence of the casting dispersions is lenesulfonate (BXG) are added, the rheological behavior is mainly also important. determined by the interactions between the gelatin and the surfac-A first, important step in analyzing the various interactions tants in the continuous phase. If soft particles with ionic shells in a gelatin color coupler dispersion is a detailed study of are dispersed in the aqueous gelatin, the viscosity is more strongly the interactions between gelatin and surfactants in aqueous increased than predicted by the hard sphere model. Upon further solution. Previous studies (4-7) indicate that the viscosity addition of a surfactant, the primarily pseudoplastic flow behavior of aqueous gelatin solutions is increased upon addition of becomes more and more Newtonian, presumably due to depletion anionic surfactants depending on their hydrophobic chain of originally surface-adsorbed gelatin molecules. The stabilization of the latex is changed from steric to electrostatic. If large amounts length. This is due to formation of so-called ''micellar gelaof surfactant are added, depletion flocculation is most likely to tin-surfactant complexes.'' At high surfactant concentraoccur. A model of the gelatin-latex-surfactant interactions is pretion, the viscosity decreases again, because free micelles are sented which takes into account the surface characteristics of the formed in the solution. The next important step is a study particles. ᭧ 1997 Academic Press of the effect of a dispersed phase on the flow behavior of Key Words: rheology; gelatin; latex particles; anionic surfacaqueous gelatin solutions. A few attempts in that direction tants; interactions; depletion flocculation. have already been undertaken. Chen and Dickinson studied protein-surfactant interactions in model emulsion systems with n-hexadecane at gelatin concentrations below 1% (w/