The formation of an epitax between silver carboxylates and silver bromide in the initial stages of silver soap crystallization

The presence of an epitaxial interface between the silver carboxylate and silver bromide nanocrystals in photothermographic imaging materials has been debated for many years. This type of an interface has been observed in model systems, and the reaction conditions used to prepare the silver soap (in the presence of the silver bromide) are conducive to the formation of that interface. In order to determine if this interface can be detected at any stage of formation of the silver soap during its preparation in the presence of silver bromide nanocrystals, we have undertaken cryogenic TEM investigations to freeze the reaction and reveal the formation of the silver stearate (AgSt) microstructure at the very initial stages of the reaction, which precedes significant crystal lattice formation. We found 5 nm-sized AgSt micelles, which aggregate to produce larger (50-100 nm in size), loosely packed crystals, but AgSt nucleates on AgBr when 50 nm cubic grains are added to the NaSt dispersion prior to the AgNO₃. After nucleation, the AgSt micelles form structures via an epitaxial interface on at least one corner of every available AgBr cubic crystal. Complete details of this reaction process and the implications to subsequent silver soap crystal growth will be discussed in this talk.