Effects of Deformation on the Properties of Emulsion Grains

Abstract

Emulsion grains have been deformed by bending an emulsion layer coated on film, and the effects of deformation on the dispersity ol photolytic silver and on the number and distribution of development centres have been studied. The observations show thai a major effect of such treatment is to increase the number of sues within a grain at which silver specks can be nucleated.

The usual sensitomelric effect of such changes is to increase sensitivity on internal-image development at the expense of sensitivity on surface-image or conventional development. However, it is shown that surface desensitizalion may be accompanied sometimes by internal desensitization rather than sensitization. The internal desensitization can be attributed to competition between the increased number of internal sensitivity centres. Support for this view was obtained from the fact that changes in the effect of deformation on storage prior to exposure (decrease of surface desensitization. decrease of internal sensitization or desensitization I were associated with a reduction in the number of centres ,il which internal silver could be nucleated.

A further effect of deformation noted with coatings of lodohromide emulsions (but probably general with respect to halide) is to decrease the luminescence intensity at low temperatures, particularly at low intensities of excitation, and to increase the time required for luminescence to reach maximum intensity. These observations show that deformation introduces new recombination centres and electron traps into emulsion grains The connection between the effects of deformation on sensitomelric properties and luminescence properties have been studied as a function of grain size and chemical sensitization in a series of animoniacal emulsions. The findings confirmed that damage to the grains is responsible for the loss of sensitivity on conventional development, and that chemical sensitization, though reducing desensitization hv deformation, has no influence on the grain disorder introduced by this latter treatment. 11 is thought unlikely that the new recombination centres play any significant part in the desensitization by deformation of emulsions chemically sensitized so as lo be al or near optimal speed, but some contribution would appear feasible in the case of emulsions at a low level of sensitization.