REDUCTION AND AGGREGATION OF SILVER IONS IN AQUEOUS GELATIN SOLUTIONS

Radiolytic reduction of silver ions and the subsequent formation of silver clusters were studied in aqueous gelatin solutions and are compared with the parallel processes in aqueous solutions. The presence of gelatin in the solution affects the early processes, via complexation of Ag+ ions with the amino acid moieties of the gelatin. The ratio of Ag+ to gelatin chains predetermines the kinetic consequences to the agglomeration processes. This ratio may accelerate or inhibit any of the processes that involve silver ions (reduction as well as growth). The complexation reduces somewhat the rate of reduction by hydrated electrons. However, when all the ions are complexed to the gelatin, the agglomeration may become very fast; at the extreme the agglomeration rate is determined by the rate of reduction. Some of the small Ag-n(m+) bind to the gelatin stronger than Ag+ ions. Excess silver ions enhance the stability of smaller transient clusters in the presence of gelatin. Three long-lived aggregates of different sizes are stabilized by the gelatin upon complete reduction of the silver ions.