A study of effect of cyanine dyes on ionic conductivity of AgBr grains

Abstract

(1) On adsorption to cubic AgBr grains, both a 9-methyl-thiacarbocyanine (dye 1) and a 5,5′-dichloro-9-ethyl-thiacarbocyanine (dye 2), increased the conductivity of the grains with interstitial silver ions as carriers, repelling silver ions at the surface kink sites into interstitial positions. (2) On adsorption to octahedral AgBr grains, both dyes 1 and 2 increased the conductivity of the grains with mobile silver ions on the surface as carriers, whereas neither dyes 1 nor 2 increased the conductivity of the grains with interstitial silver ions as carriers. It is considered that the dye molecules repelled silver ions at surface sites, not into interstitial positions, but into surface sites where silver ions are mobile. (3) Dye 1 was preferably adsorbed to (100) faces on the surface of tetradecahedral AgBr grains, increasing the conductivity of the grains with interstitial silver ions as carriers, and was then adsorbed to the (111) faces after the saturation of the (100) faces by the dye, giving little influence on the ionic conductivity. On the contrary, dye 2 was preferably adsorbed to the (111) faces, giving little influence on the conductivity, and was then adsorbed to the (100) faces after the saturation of the (111) faces by the dye, increasing the conductivity. This result provided a method to examine the kind of faces on the surface of silver halide grains. (4) The observation of preferential adsorption on different crystal faces was successfully used to prove the presence of (100) faces on the side surfaces of a twinned tabular grain.