Silver aggregates

Fig. 12. A possible mechanism for the dye-induced photooxidation of a silver center, x represents the distance across a silver haUde surface to which aggregated dye molecules are adsorbed. Steps 1, 4, and 5 represent the photohole (Q) formation, photohole migration, and silver oxidation processes which can ultimately lead to the total regression of the silver aggregate ( ) represents an energy state occupied by an electron.

Welker, T., 1978. Optical absorption of matrix isolated silver aggregates and microcrystals, Ber. Bunsenges. Phys. Chem., 82, 40-41. 

Interestingly, non-metallic silver clusters, depending on their sizes, may act either as electron donors or as electron acceptors. Using sulfonatopropyl-viologen, SPV (E° for SPV/SPV- = — 0.41 V/NHE), pulse radiolysis established that small silver clusters (n < 4) acted as electron donors (Le. E° for (Ag /Agn < E° for SPV/SPV - ) while, conversely, large silver clusters (n 2 4) were electron acceptors (i.e. E° for Ag/ /Agn > E° for SPV/SPV- ) [511]. Size-dependent electrochemical potentials of silver aggregates have been elucidated (Fig. 82) [506]. 

Because the critical size of a silver aggregate for latent image aggregates becomes smaller with increasing intensity of the exposing radiation, Moisar holds that not only is low-intensity reciprocity failure explained, but it is required. 

Properties of Linear Silver Aggregates Calculated by CNDOa... 

Electronic Properties. When the silver aggregate grows, its properties become more like those of bulk silver. These calculations for Ag atoms added at lattice positions show that a single atom on the crystal has a charge of +0.52, which is comparable to the average AgBr lattice cation charge of +0.55 calculated by... 

Another example of the determination of a redox equilibrium by pulse radiolysis is the measurement of the reduction potential of silver aggregates, Ag , as a function of the aggregation number n. Such measurements are of intrinsic value in understanding photographic development processes [70],... 

Mostafavi et al. [92] generate very small silver aggregates by a pulse radiolysis method and follow their aggregation and growth in the presence of an electron donor, the radical anion of sulfonatopropyl viologen (SPV) generated in the same pulse. They use this method to study the size dependence of the electrochemical potential of small silver clusters and conclude that a critical silver aggregate is Ag5+/Ag5, which has E° = —410 mV (NHE). 

Danilova, Y.E., Lepcshkin, N.N., Rautian, S.G., Safonov, V.P. Excitation localization and nonlinear optical processes in colloidal silver aggregates. Physica A 241, 231—235 (1997)... 

MOSTAFAVI, M., MARIGNIER, J. L., AMBLARD, J., BELLONI, J., Size-Dependent Thermodynamic Properties of Silver Aggregates. Simulation of the Photographic Development Process , Z. Phys. D 1989,12, 31-35. 

W. D. Balgord Several questioners seem to have interpreted our comments on p. 143 to mean that we actually observed monatomic Ag in the analcite. No effort was made to detect Ag atoms. In fact, the paragraph does not mention them as such. It does seem reasonable, however, that silver, if initially present as individual Ag+ ions in the restricted analcite cavities, may have existed as discrete Ag° atoms, if only momentarily, at one step in the mechanism by which the metallic silver aggregated. 

Yu. E. Danilova, Localization of Optical Excitations in Colloidal Silver Aggregates PhD Thesis (Institute of Automatics and Electrometry RAS, Novosibirsk, 1999). 

PEG is flexible, and water-soluble neutral polymer can serve as a dispersant because of its ability to bind water. In this work bare or coated with PEG (Mw - 8000, 5 mg/ml) silver nanoparticles were heated at 90°C for 20 min. Heating of bare silver nanoparticles resulted in silver coagulation and formation of the large aggregates (Fig. 3a) while heating of PEG modified silver nanoparticles lead to the destruction of silver aggregates and effective stabilization of single nanoparticles (Fig. 3b). 

Figure 9.10 Surface area distribution based on spherical particles compared with the surface area distribution for silver aggregates using the theory of Lall et al. [138] for idealized aggregates. Primary particle size 18.5 3.5 nm. Reproduced with permission of Elsevier.

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