CrystaI Habit and Rounding of Cubic Silver Bromide Grains

摘要

The results of two analytical procedures, viz., percent cubicity by dye adsorption and supersphere roundness index, Q, by electron image analysis (electron microscopy) were compared for a series of cubic AgBr emulsions. A linear, least square, correlation, /100 cubicity = -110.7 Q + 99.96, was obtained in the range 0.25 < Q < 0.65. The zwitterionic dye, 3-ethyl, 3'-(3-sulfo-butyl)-9- methyl-thiacarbocyanine, as used in the cubicity test, adsorbs on rounded AgBr cubes either as single molecules or as J-aggre- gates. When cubes are slightly or moderately rounded, the demarcation of these two modes of adsorption can be identified with a "tilt" of the grain surface between 9 and 13: only small deviations from the (100} crystal habit suffice to cause the dye to adsorb as J-aggregates.