SELFORGANIZATION AND SILVER-HALIDE PHOTOLYSIS

We show that certain criteria for selforganizing systems, namely thermodynamic control and structural specificity of the products, determined by weak bonding therein, are met by the photolabile silver halides which yield Ag-n(o) clusters on irradiation. Laser flash photolysis (35 ps pulse, 355 nm) of sub-mu m, cubic photographic emulsion grains, AgBr and Ag(I)Br, dispersed in gelatin, leads to reversible formation of light absorbing transients assigned to these clusters. Under our conditions two unique values, or, at least, narrow distributions of cluster nuclearity appear to obtain. Nucleation and cluster growth occur at the grain surfaces, i.e. AgBr-gelatin interface. Further studies are required to establish size and structure of the clusters which evolve under these conditions to see if the criterion of modular construction, as envisioned in the clusters of clusters model(1), is actually realized in this chemistry.