The results of an investigation of the sites of silver halide formation on the surface of silver carboxylate crystals, modeled by silver stearate and prepared by the standard in situ process used for thermally developed photographic materials, are reported. For the first time the structure of a silver halide/silver carboxylate interface has been clearly observed. Silver bromide is found to form on the edges of the silver stearate crystal during the initial stages of the reaction. The influence of the nature of the halide source on The silver halide shape and location on the silver carboxylate crystal and the presence of defects in the silver halide crystals are discussed.
The purpose of this paper is to establish that significant differences exist between mechanisms of latent image formation in conventional silver halide emulsions and in dry processed, photothermographic silver media. We develop our analysis in two ways: (1) through a review of salient literature; and (2) by highlighting areas of research that clearly delineate between conventional silver halide and photothermographic media, involving mathematical modeling, laser spectroscopy, and photocharge studies. We conclude that catalytic juxtaposition of a silver carboxylate phase with a silver halide phase leads to profound changes in the photophysics of the silver halide. Thus characteristically different latent-image-forming mechanisms prevail in thermally developed media, compared with conventional, negative-working silver halide photographic films, and transfer of technology from one to the other is not obvious.
We have carried out electrochemical, sensitometric, and electron microscope investigations of the reactions of the photosensitive phase of a thermally developable photomaterial. We have found that formation of icrocrystals of silver bromide by metathetical reaction of silver stearate with bromide in aqueous solution leads to precipitation of silver bromide as a separate phase, accompanied by dissolution of silver stearate microcrystals. The size of the AgBr microcrystals increases with increasing concentration of the brominating agent, but does not exceed 0.07 μm. Latent image centers formed by the AgBr microcrystals are capable of catalyzing thermal development if the microcrystals have been formed in the presence of the carboxylate. The process of thermal amplification of the latent image centers may, however, be achieved on AgBr crystals having no physical contact with silver stearate. We propose that thermal development of latent image centers on AgBr crystals proceeds by diffusion of silver stearate-derived “droplets” to the development centers. Fog formation, on the other hand, nucleates independently of the AgBr microcrystals.
The morphology of thiacarbocyanine and oxacarbocyanine dye J-aggregates adsorbed on (001) surfaces of AgBr microcrystals grown in gelatin was observed by atomic force microscopy. No residue of fibrous gelatin was found on the specimen. The cyanine dyes grew in islands or stripes by means of the Volmer- Weber growth mode, rather than by monolayer adsorption. The thickness of stripes varied from 0.5 nm (monolayer) to 30 nm, and the stripes were constructed of many rectangles [20 ×(35−50) nm]. The rectangles were regarded as elementary crystallites or J-aggregate particles photoelectrically separated from one another.
The crystal and molecular structure of [bis-(2-tribromomethylsulfonyl-benzothiazole)-silver(I)-tetrafluoro-borate·(acetone)] solvate, [Ag{(C7H4NS)SO2CBr3}2BF4·Me2CO], has been determined by single crystal x-ray analysis. The space group is P21/c, a = 16.985(5) Å, b = 10.426(3) Å, c = 19.693(4) Å, β = 111.78(2)°, V = 3238 Å3. Chelation by the 2-tribromomethyl-sulfonyl) benzothiazole ligand occurs through the ring nitrogen and sulfone oxygen, resulting in a distorted tetrahedral configuration around the silver atom. This complex is proposed as part of an alternative model for fog center removal in silver halide photographic constructions, in contrast to the theory of bromine radical formation from tribromomethyl compounds. Compounds containing tribromomethyl groups, which also possess sites capable of coordinating with a silver halide surface, may act as ligands to position the bromine on the silver halide surface. This placement of the bromine near the fog centers is suggested as a route to enhance the efficiency of this class of compounds as antifoggants.
The experimental reproduction of the whole process invented by Nicéphore Niépce around 1824 is presented. This work is based exclusively on the original manuscripts of Niépce from 1816 to 1833. The true principle of this invention is explained, and the different steps of Niépce's research are detailed. The sensitivity of the process and the resolution of the images are determined. All the results confirm that Niépce is the inventor of photography and also of photoengraving processes.
A review of color holography is presented as an introduction. A new method of recording and processing high-quality color holograms in an ultrahigh-resolution silver halide emulsion has been developed. Color reflection holography presents no fundamental problems with regard to the geometry of the recording setup, but the final result is highly dependent on the recording material used and its processing. By the introduction of extremely high-resolution panchromatic emulsions it has become possible to obtain high-quality, large-format color reflection holograms. The use of three laser wavelengths on a single-layer emulsion in the recording process makes the holographic recording technique similar to the early Lippmann photography technique of the last century. That combination not only promotes good color rendition, but, additionally, because no dyes or pigments are used in the emulsion of the final hologram, high archival color stability can be predicted for the image. The recording procedure, employing a Denisyuk setup and three laser wavelengths, and the processing technique are described. The processing of such holograms is critical to obtain high diffraction efficiency and good color rendering. In particular, the prevention of emulsion shrinkage is extremely important. Color holograms up to 30 × 40 cm have been recorded.
A new technology for printing three-dimensional solid objects from computer-generated images is described. The technology is based on extrusion of a thermoplastic polymer melt as small fibers that bond to form the solid object. This technology is referred to as thermoplastic melt extrusion rapid prototyping (RP). Polymer materials for thermoplastic melt extrusion RP must have the ability to form the structural building blocks of the part. These building blocks are walls, shelves, and bridges. The flow and deformation (rheology) of the melt as it is extruded through the circular die and adheres to the layers already in place govern the process. At this exploratory stage of development, there is no model to specify the extrusion conditions and materials properties relationship to RP performance. Ten marginally acceptable RP materials were identified through extensive RP testing. This study presents the preliminary rheological and thermal analytical characterization of these materials. Characterization of the melt properties is fundamental to the development of a constitutive equation for modeling and to an understanding of the process. The most promising RP materials were found to be crystallizing polymers. Isothermal rheometry and calorimetry measurements were performed to study the crystallization kinetics. Solidification due to crystallization during extrusion is expected to play a key role in RP materials performance.