The Colloidal Stability of Spectrally Sensitized 3-D AgClI Emulsions

Abstract

The colloidal stability of silver halide emulsions precipitated in aqueous gelatin media is predominantly electro-steric in nature and is provided by gelatin adsorbed on the silver halide grains. It is believed that gelatin provides adequate colloidal stability for spectrally sensitized silver halide emulsions, where the sensitizing dyes compete with gelatin for the silver halide surface. We have examined the details of the interaction of gelatin with unsensitized and sensitized 3-D AgClI emulsions by evaluating the interfacial potential of the emulsions and their colloidal stability as a function of pH and ionic strength. The interfacial potential of the emulsions has been determined using electrokinetic sonic amplitude (ESA) measurements and the colloidal stability of the emulsions was studied using filterability measurements. The unsensitized and sensitized emulsions do not show any appreciable differences in their electrokinetic properties, while they do exhibit differences in their filterability properties upon pH cycling. It is surmised that gelatin is more easily desorbed from the surface of sensitized emulsions than unsensitized emulsions upon pH cycling, leading to aggregation. Hence, we conclude that the weaker adsorption of gelatin on silver halide emulsions is the root cause of the diminished colloidal stability of spectrally sensitized silver halide emulsions. The results suggest that sensitized silver halide emulsions are more prone to destabilization due to process variations than unsensitized silver halide emulsions.