AgBr Particles Research Articles

Fluorescence Quenching of Cyanine Dyes Adsorbed onto the Surface of Colloid Semiconductors

AbstractThe kinetics of interfacial energy transfer have been studied with colloidal TiO2 and AgBr particles, which form transparent aqueous dispersions. The fluorescence spectra and decay for both systems have been determined and discussed. The quenching of fluorescence emission of a sensitizing dye by a supersensitizer has been observed. The super-sensitizer shortens the fluorescence lifetime of the supersensitizing system, which has been determined by nanosecond time-resolved fluo-rescence spectroscopy. It is concluded that the Dye-Dye interaction plays an important role in the photographic process. Some rigidized cyanine dyes nave also been studied.

The theory of the nucleation of monodisperse particles in open systems and its application to agbr systems

The theory of the nucleation process has been developed for monodisperse sparingly soluble colloidal particles in an open system, where the monomer source (a combination of the reactants or a single reactive component to be reacted with a counterpart in the system) is introduced from outside at a constant molal feed rate ( Q), and the rates of growth and dissolution of the particles are both limited by the diffusion of the monomer complexes. The theory is based on a nucleation model where stable nuclei as origins of the product particles are produced through a kind of Ostwald ripening from stationary unstable nuclei that are in a quasi-steady state of balance between the generation of their embryos by instantaneous reaction of the introduced reactants and either dissolution or growth. It leads to the final particle number, n + ∞, the mean radius of the stable nuclei at the end of the nucleation, r + n , and the nucleation time for the production of the stable nuclei, t n; i.e., n + ∞ = 1.567QRT 8πDσV m C ∞ , r + n = 1.638 r p, and t n = 5.097RTv p 8πDσV m 2C ∞ , where R is the gas constant, T is the absolute temperature, D is the diffusion coefficient of the monomers, a is the specific surface energy of the solid, V m is the molar volume of the solid, C ∞. is the solubility of the solid, and r p and v p are the maximum radius and the maximum volume, respectively, of the embryos within their size distribution range. The theoretical conclusions have been confirmed by experiment for the formation of monodisperse AgBr particles, and the mean radius as well as the maximum radius of their embryos was evaluated.

THE EFFECT OF ALKANES ON THE FORMATION OF ULTRAFINE SILVER BROMIDE PARTICLES IN IONIC W/O MICROEMULSIONS

ABSTRACT Ultrafine AgBr particles formed in w/o microemulsions with different chain length of alkanes were studied by UV-VIS spectrophotometry, stopped-flow spectrophotometry and transmission electron microscopy. The ultrafine particles of AgBr (5-7 nm in diameter) were obtained by mixing two separately prepared microemulsion systems both containing AOT, n-hexane and an aqueous solution of either AgNO3 or NaBr.The size distribution of the nearly spherical AgBr particles broadened from 5 to about 10 nm as chain length of alkane was increased from n-hexane to n-octane. When n-dodecane or a higher alkane was used, the microemulsion system became increasingly unstable causing precipitation of AgBr.

Mechanism of halide conversion process of colloidal AgCl microcrystals by Br − ions : I. Observation of the dynamic changes in shape, structure, and composition

The mechanism of the halide conversion process in suspension of AgCl microcrystals by bromide ions was studied by electron microscopy, X-ray diffractometry, and electron-beam diffractometry. The typical conversion process after the introduction of Br − was found to consist of more than three distinctive steps. The first step was an almost instantaneous reaction within a few seconds for a surface conversion without apparent morphological change of the original particles. The second step was a very rapid epitaxial growth process of virtually pure AgBr crystals on every corner and partly on the edges of the AgCl cubic microcrystals with dissolution of their own {100} faces, which was finished in about 1 min at 25°C. The third step was a much slower process of about 2 h at 25°C (ca. 5 min at 45°C) for the formation of an AgCl 0.5Br 0.5 solid solution developing from the joints of AgBr guest and AgCl host by simultaneous dissolution of the guests and the hosts. After the complete dissolution of the AgBr guests, a further recrystallization process that formed a solid solution richer in chloride content followed. Finally, the conversion virtually stopped midway to yield double-structured particles of Ag(Cl, Br) shell/AgCl core. However, when the initial molar ratio of [Br −] 0 [AgCl] 0 was so high as to exceed unity, the original AgCl particles were totally decomposed into about eightfold AgBr particles in number. In this case the steps later than the second one were missing. Also, it was suggested from the subsidiary study on open systems, where bromide ions were added continuously, that the kinetics was basically controlled by the deposition rate of the solute of the AgBr component of the growing parts, though it was switched to being limited by the dissolution rate of the host AgCl crystals when their open surface area for dissolution was extremely diminished.

Sodium Dodecylsulphate Electrophoretic Demonstration of Selective Adsorption of Gelatin Polypeptides on Silver Halide Particles-A Qualitative Examination

AbstractThe gelatin fraction adsorbed on silver iodobromide particles was recovered by dissolution of the particles with sodium thiosulphate. The sodium dodecylsulphate, SDS, electrophoretic pattern of the recovered fraction was clearly different from that of the original gelatin. This is a direct indication of selective adsorption. Extraction of the adsorbed gelatin from the particles was examined with several reagents. Among them, the SDS extract gave a similar electrophoretic pattern to that of the fixation-recovered fraction. Electrophoretic patterns of SDS-extracted fractions from AgCl, AgBr and Agl particles indicate that the absorptions by these silver halides are selective and selectivity by each silver halide is different.

DEPOSITION OF METALLIC and SEMICONDUCTING LAYERS ONTO BILAYER LIPID MEMBRANES

In this paper the phenomenon of inorganic substances deposited onto the bilayer lipid membrane is described. Metallic copper and semiconducting compounds such as CuS, FeS, CdS and also AgBr were deposited onto the bilayer lipid membrane. The cyclic voltammetry technique was used for determining electrochemical and photoelectrical properties of coated membranes. Considerable increase of stability and drastic changes of membrane properties were observed. Also investigated were the photoelectrical properties of bilayer lipid membrane with dispersed CdSe or AgBr particles in the absence and presence of pigments.

Determination of gelatin-layer thickness on AgBr by means of a disk centrifuge

The usefulness of the disk centrifuge in the determination of adsorption-layer thicknesses was demonstrated on aqueous dispersions of AgBr with particle diameters in the tenths of micrometers. The hydrodynamic thickness ( L) of the gelatin layer was calculated from the sedimentation rates of the gelatin-covered and of the hare AgBr particles from which gelatin had been removed by enzymatic decomposition. Depending on the sample, at low ionic strength (1 m M NaNO 3, pH ∼ 6) great differences of L were observed, ranging from 0.024 to 0.148 μm. In most cases L decreased significantly with increasing ionic strength. The variation of L with pH was studied with two samples. One showed a minimum at the isoelectric point, the other a monotonic decrease of L with pH through the isoelectric point. The high values of L observed in some of the samples suggested multilayer formation in the presence of free gelatin. Multilayers could be detected under altered experimental conditions, but in all likelihood did not affect our results.

Stable crystal habits of general tetradecahedral microcrystals and monodisperse agbr particles. II. Steady forms in open systems

The kinetic theory of the habit modification of general tetradecahedral particles was developed for the following typical cases in open systems: (a) both growth rates of (100) and (111) faces are reaction controlled; (b) one is reaction controlled while the other is diffusion controlled; (c) both are diffusion controlled. The theory led us to the conclusion that if both (100) and (111) faces grow by ideal diffusion control, the steady growth form is equal to the equilibrium form. Also, a graphic method to determine the steady forms in general open systems has been established. Moreover, non-steady growth forms were considered in contrast with the steady forms. As an application of the non-steady diffusion-controlled growth a method to estimate absolute values of specific surface energies of (100) and (111) faces for a tetradecahedral microcrystal was proposed. The experimental results as to the crystal habit of AgBr particles in open systems and the effect of ammonia were elucidated in the light of the above theoretical consideration.

Stable crystal habits of general tetradecahedral microcrystals and monodisperse agbr particles: I. Equilibrium forms and steady forms

A general theory of the stable forms of tetradecahedral microcrystals has been developed by introducing the surface chemical potentials of the (100) and (111) faces. The theory describes the dynamic nature of the equilibrium form and the steady form defined as a growth form in the steady state and the relationship between them. Experiments were conducted on monodisperse AgBr microcrystals, and both stable forms of AgBr were determined as functions of p Br in gelatinous aqueous solution by use of a dye adsorption method. The experimental results were elucidated in the light of the theory.

The use of film methods in small-angle X-ray scattering

Various sources of random deviations occurring in the determination of X-ray intensities with the aid of film methods are discussed and corresponding mathematical expressions are derived. From a comparison with experimental values of the standard deviations obtained from measurements on homogeneously exposed films, it follows that the deviations are primarily caused by the variations of the X-ray photon flux due to the stochastic nature of the X-ray emission process. The accuracy attainable with most X-ray films is found not to be limited by saturation of the number of excited AgBr particles occurring at increasing exposures, but at low exposures film methods are at a disadvantage because of the presence of fog. If, however, small signals superimposed on a high sample background have to be measured, relatively high exposures are required; in this case film registration is found to be much faster than methods involving step-scanning counters, and in general little slower than registration with the aid of a position-sensitive counter. It is also shown that the dynamic range of the film method may be extended without sacrificing accuracy by resorting to slower films.

On the Crystal Habit and Particle Size Distribution of AgBr Emulsions Prepared in the Presence of Synthetic Colloids

AbstractAn account is given of the further experiments concerning the particle size distribution and crystal habit of AgBr particles in emulsions prepared in the presence of synthetic colloids such as polyacrylamide. paly-N-methylacrylamide and polr-N,N-dimethylacrylamide. The data have been obtained by examination of the emulsion with on electron microscope.