Silver emulsion, conventional

Comparison of Conventional Silver Emulsion and Unconventional Polymer Image Recording... 

Pearlman and associates (63) found that sprayed emulsions prepared from silver bromide could be sulfur-sensitized by conventional means, but the increase in sensitivity was only twofold. The increase for grains prepared with 99% AgBr plus 1% Agl, on the other hand, was tenfold. They did not detect a difference in structure between the pure bromide and the iodo-bromide grains. The response of equimolar chlorobromide grains to S-sensitization also was greater than that of the pure bromide. 

The number of dye molecules adsorbed by a silver halide grain in conventional sensitized emulsions is large. If the area occupied by an adsorbed molecule is 60 A2, an area close to that estimated for several cyanine and carbocyanine dyes, the number of molecules per square micron at monolayer coverage would be... 

With old-style emulsions, such as Efke 25, 50, and 100, it was possible to use methods found in the 2nd edition of the Cookbook, such as the Hydrogen Peroxide Pushing Method or Acetic Acid Intensification, to create a true increase in film speed. Unfortunately, modern emulsions, whether they are conventional or flat-grained, rely on color dye sensitization to achieve their sensitivity as much as upon silver sensitivity. Color dyes do not respond to these speed increasing techniques. Hydrogen peroxide will do little or nothing and acetic acid latensification may ruin your film. I no longer recommend either. 

To obtain a Russell image, flat objects can be placed in direct contact with the film overnight. With thin, flat objects this imaging can be done conveniently inside an X-ray cassette. The film is developed by using conventional fixer and developer, in this case Ilford Phenisol and Hypam, respectively, each diluted to 20 by volume of the stock concentration. The mechanism of sensitization to hydrogen peroxide is not clear but may be due to an increase in silver ion concentration in the photographic emulsion (14). 

The increased interest in energy sensitive polymers probably evolves from the shortcomings of the conventional image recording media-silver halide emulsion. It is both difficult and expensive to apply emulsion films as protective layers or use as printing plates or etch resists. Synthetic polymers are one to two orders of magnitude less radiation sensitive than halide emulsion, but their unique properties of chemical and physical resistance easily overcome this disadvantage, ( ., Table IV). 

Figure 18 Schematic representation of the preparation of Ag SPEB(PS-PAA) composite particles in situ. PS core particles are first prepared by a conventional emulsion polymerization. In the second step, the PS cores are covered with a thin layer of photoinitiator HMEM. In the third step, the shell of polyelectrolyte brushes is formed by photoemulsion polymerization Shining light on the aqueous suspension of these particles generates radicals at their surface, which initiate the radical polymerization of the functional monomer (silver acrylate) on the surface of the core particles. Concomitantly, the silver anions embedded in the PAA brushes are reduced to Ag-NP under UV irradiation. Reprinted with permission from Lu, Y. Mei, Y. Schrinner, M. etal.

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