The Adsorption of Gelatin to a Silver Powder

A silver powder was prepared by borohydride reduction of freshly precipitated silver bromide. Its surface area was estimated by dye adsorption to be 1·6m²g.^–1. The adsorption of gelatin from solution at pH6 was studied and isotherms were derived at 25° and 35°C. The results showed features typical of polymer adsorption generally. For gelatin concentrations below about 0·25 per cent, adsorption was not detectably dependent on temperature. Above this level, adsorption is greater at 25°, which is attributed to the effect of gelling forces in the adsorbed layer. A Langmuir plot of the 35° isotherm was approximately linear. The adsorbed gelatin could not be desorbed. The last fact does not necessarily forbid the application of equilibrium thermodynamic theory, since the apparent irreversibility may reside solely in the need to desorb many polymer segments simultaneously. Heat of adsorption was investigated with the aid of a microcalorimeter. With a 0·2 per cent gelatin solution, a slow heat evolution was observed over 40 mins., amounting to 2·1 millicals., or 420cal./100g., based on the weight of gelatin adsorbed. Passage of solvent then caused the heat consumption of 0·5 millicals., which, since there is no associated gelatin desorption must be ascribed to a purely entropic effect. The picture given by these heat measurements is similar to that reported previously for adsorption to silver bromide (Chem. & Ind., 1964, p. 2057). The heat of adsorption in the latter case was 1,500cal./100g. This may represent a genuine difference, but caution is nesessary because of the following factors. Heat will probably have been consumed due to desorption of solvent molecules. The average number of segments of a gelatin molecule attached to the adsorbent and the relevant energies of the possibly various groups are unknown.     

Convective Diffusion of Water in Gelatin Layers: Application of Theory to Process Optimization

Abstract

A review of the analytical theory of the convective diffusion of water in a swelling gelatin layer is presented, together with an outline of the effect of varying hardness on times of imbibition and drying. Development time is calculated using the Danckwerts' method and the appropriate diffusion coefficient, assuming that developer begins to diffuse into the layer when it is fully swollen and that a constant mass of silver is produced without significant halide loss. The total processing time is then considered as a function of layer hardness.     

The Influence of Gelatin on the Growth of Silver Halide Macrocrystals

The morphological influence of gelatin on the growth, from ammoniacal solutions, of macrocrystals of silver bromide and silver chloride has been studied.

When silver bromide grows in gelatin, tabular crystals are formed. Laue’s patterns of these crystals present a well marked asterism, resulting from an intense adsorption of gelatin.

AgCL a crystals are limited by (100) faces in the presence of gelatin and by (111) faces when there is no gelatin; the experimental conditions being of course identical in both cases.

Some ideas are presented concerning mechanisms that are likely to lead to the observed phenomenons.     

Improvements of Some Physical Properties in Gelatin Layers

The effect of copolymer formation in situ in the photographic layer by the reaction between the gelatin, a cyclodextrin derivative and a diepoxy crosslinking agent was investigated. The melting point increase, the swelling ability and the optical rotatory dispersion were determined. The photographic characteristics were investigated in silver bromide layers containing gelatin-cyclodextrin copolymer.

It has been found that the copolymer makes rapid diffusion of the developing agent possible at a low water absorption and high degree of hardening of the layer. This feature can be explained by the decrease of the hydration of polypeptide chains by copolymer formation and the favourable. spatial structure of the copolymer molecules.     

Investigation of Refractive-index Profiles of Ion-exchanged Planar Waveguides in Glass

Abstract

New data concerning the refractive-index profiles in Ag/Na ion-exchanged waveguides are obtained using a parabolic-segment reconstruction method. The profiles can be described as second-order polynomials, but with a mean curvature b = 2·8 which is significantly greater than the originally suggested value 0·64. The profile so obtained agrees very well with the common diffusion equation for the silver ion concentration only if one assumes a simple linear relationship between the diffusion coefficient and the concentration. This fact necessitates changes in present ideas about the ion-exchange mechanism in sodalime glasses.     

Physical and Photographic Properties of Polyethylene Oxides

In the presence of gelatin no adsorption of the unsubstituted polyethylene oxides {PEO) on silver or silver bromide could be detected and it must be assumed that the concentration of PEO in the adsorbed gelatin layer is the same as in the bulk emulsion. It is supposed that the adsorbed gelatin layer is made more hydrophilic by PEO. This results in: (a) an accelerated fixation of a silver bromo-iodide emulsion in a concentrated sodium sulphite solution. Especially the solution of the iodide-rich parts of the grain surface is increased probably due to a stronger hydration of the silver ions. The iodide-rich phase is important in development on account of locally formed latent image. This explains, why developers in which solution physical development plays the prominent part, are strongly activated by PEO especially in the case of iodide-containing silver bromide emulsions ; (b) a decrease of the adsorption of hydrophilic developing agents. This applies to the di-anion of hydroquinone and explains the PEO-inhibition of alkaline hydroquinone development.     

An Ellipsometric Study of the Adsorption of Gelatin on Silver Bromide

Optically-polished surfaces of silver bromide were examined by ellipsometry to establish their optical properties. The adsorption of gelatin onto the surfaces from an aqueous solution at 40° C was then followed ellipsometrically. Measurements were carried out as a function of time and as a function of pH at pBr 3. From the measurements, it was possible to obtain the adsorption excess of the gelatin at the surface, the optical thickness of the adsorbed layer and the concentration of gelatin in the adsorbed layer. The optical thickness of the adsorbed layer was found to vary significantly with pH and to reach a maximum value of ca. 400 A at the isoelectric point of the gelatin.     

The Adsorption of Gelatin to Silver Bromide Microcrystals

A strong bond formation between the aspartic acid residues of gelatin molecule and the silver bromide surface in various conditions gives good reason to believe that these residues are the groups by means of which the gelatin adsorbs to the silver bromide; this must be a true chemisorption. Such assumption allowed one (a) to calculate the length of a segment (ioop) of a single-chain gelatin molecule between the possible points of adsorption and (b) to draw some conclusions on the thickness and structure of gelatin adsorption layer on the silver bromide microcrystals. These results are in good agreement with the data of other authors.     

The Penetration Rate of Photographic Chemicals into Gelatin Layers and into Emulsion Layers under Development

The infiltration rate of water through dry gelatin layers and the penetration rate of developing agents, OH^-, HCHO and other organic and inorganic developer ingredients through gelatin layers, gel or emulsion layers were determined by five methods.

The penetration of OH^- through gelatin layers depends considerably on pH, ionic strength and total alkalinity and, in spite of its high mobility in water, it penetrates slower than developing agents at the pH and ionic strength of normal developers due to consumption by gelatin.

Under diffusion-controlled development of emulsion layers, the distance of penetration of developing agents was roughly proportional to the square root of the penetration time, but the apparent rate was 1 or 2 orders of magnitude slower than that for a simple gelatin layer, depending on Agx/gelatin ratio and degree of hardening of the layer.

The results from direct comparison of penetration of developing agents and OH^- in the same emulsion layer under diffusion-controlled development showed that, higher swelling, lower hardener content and higher Agx concentration proved more favorable to the reduction controlled by penetration of developing agent, rather than by that of OH^-.

The experiments also show that, in rapid processing by developer of high pH and high ionic strength, the rate of water infiltration becomes important for the rate of development, in its early stages.     

Experimental Design Applied to the Study of the Flocculation of Modified Gelatin

This paper describes the use of the experimental design methodology in order to compare the flocculation behaviour of two types of modified gelatins [phenylcarbamyl gelatin (CNP type) and phthalyl gelatin (PH type)I in a medium con-taining silver halides and during two successive flocculation steps.

The influence of five parameters has been studied: the total quantity of gelatin added; the type of modified gelatin used; the ratio of inert gelatin to modified gelatin; the temperature of precipitation of the silver halide; and the acid used for flocculation pH adjustment.

Three main conclusions can be drawn.

The dominant parameters controlling flocculation are the type of modified gelatin chosen and its ratio to inert gelatin during flocculation.

The pH for flocculation in the first flocculation step is always equal to, or lower than, the pH in the second one.

The pH for flocculation in the second step is higher when using the phenylcarbamyl-type (pH max = 4.7) as compared to the phthalyl-type gelatin (pH max = 4.3).     

Rheological investigation and its correlation with permeability coefficient of drug loaded carbopol gel: influence of absorption enhancers

Context: The present study was planned to investigate the effect of absorption enhancers on the microstructure of Losartan potassium gel and hence its influence on the diffusion of Losartan potassium across nasal mucosa.

Method: Losartan potassium loaded carbopol gel (1% w/v) with and without absorption enhancers was prepared. Polyethylene glycol (PEG) 4000 and ethanol were used as absorption enhancers. Microstructural elucidation of prepared gels was done using shear rheology. Ex vivo drug release studies were performed on the prepared gels.

Results: It was observed that the absorption enhancers PEG 4000 and ethanol altered the gel microstructure. The prepared gels were viscoelastic in nature suggesting their suitability for topical application. Permeability coefficient of Losartan potassium loaded into gels was found to be inversely proportional to the storage modulus. Thus increase in storage modulus lead to slow drug diffusion.

Conclusion: The current study emphasizes on the fact that selection of polymeric carrier for nasal drug delivery and/or absorption enhancer strongly influence the microstructure of the gel and hence the pharmaceutical performance of the formulation.     

Physical Ripening of Photographic Emulsions with Hardened Gelatin

The paper presents information about the conditions in which the hardeners formaldehyde and chromic acetate can effect the kinetics of the physical ripening of “neutral” and ammoniacal silver bromide emulsions obtained at various excesses of potassium bromide. When a gelatin is partially hardened, there is no effect on the physical ripening of fine-grained emulsions. The crystal growth is restrained as a consequence of the hardening only when the emulsion grains are larger. In this case it is assumed that on the grain surface are formed thicker or more compact adsorption layers of gelatin, which reduce the rate of the diffusion processes and, hence, the rate of crystal growth. Chromic acetate exerts very strong restraining action on ammoniacal emulsions. This effect is explained not by the hardening of gelatin, but by the formation of chromic ammonia complex ions, which block the active centres of crystal growth on grain surface.     

Colour Separation of Pictures In High-Speed Photography

Single layers of silver bromide crystals about 0.1μ in diameter attached to microscopic slides were prepared by evaporating silver under vacuum onto the slide and converting this to silver bromide in bromine vapour. The slides were then placed in a gently flowing solution consisting either of 0-1M ammonium bromide or alternatively, of OJM ammonium bromide and 1% gelatin. The solutions were kept slightly supersaturated with respect to silver bromide by cooling them before they passed over the samples. Under these conditions some of the crystals grew to a diameter of a few microns while remaining attached to the glass slide.

Thin tabular crystals were obtained. Gelatin slowed down the growth rate and, under the conditions used, led to the formation of crystals of more regular shape.     

Holographic Optical Beam Splitters in Dichromated Gelatin

Abstract

Holographic beam splitters can split an incoming beam into several partial beams travelling at different angles with arbitrary intensities, thus offering high design flexibility. In this paper the fabrication of beam splitters as multiplex holograms in dichromated gelatin is reported. Shrinking or swelling of the gelatin was avoided by careful process control, reciprocity law failure (as expected from silver halide holograms) was not observed, and, for example, a 1 : 2 beam splitter diffracting 47·4% and 47·0% of the incoming light into two higher orders was realized.     

Solid-state field-assisted silver diffusion in (TeO2)0.6(WO3)0.25(La2O3)0.05(Na2O)0.1 glass

Silver-doped layers have been produced in (TeO₂)_0.6(WO₃)_0.25(La₂O₃)_0.05(Na₂O)_0.1 (TWLN) glass by solid-state field-assisted diffusion. The silver concentration profile in the glass has been determined by secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS). The Matano-Boltzmann method applied to thermally activated diffusion indicates that the silver diffusion coefficient in the glass is a weak function of silver concentration. We carried out modeling of silver concentration profiles in the doped layer of the TWLN glass after solid-state field-assisted diffusion. Good agreement of the theoretical fit and experimental data suggests that the model chosen can be used to describe solid-state field-assisted diffusion of silver ions in TWLN glasses. Using RBS data, we have quantitatively estimated the surface density of silver atoms after field-assisted diffusion. Combining SIMS and RBS, we were able to assess the absolute silver concentration depth profile. Our results demonstrate that field-assisted diffusion, a simple and effective procedure for doping optical glasses, can be used to produce planar waveguide structures based on the tellurite glass studied here.     

Adsorption of Gelatin to Silver Bron1ide

Adsorption and desorption isotherms for gelatin on silver bromide at both pH 6 5 and 3 5 were obtained. At pH 6 5 the adsorption was higher than at pH 3 5 but a proportion of the gelatin was desorbable. There was no detectable desorption at pH 3-5. In addition the effect of adsorbed gelatin on the fixation time of silver bromide sols was examined. The decrease in fixation time observed with added gelatin was most marked at pH values below the isoelectric point, and at the lower temperatures examined. It is concluded that the net charge on the gelatin molecule in relation to the charge on the surface plays an important part in the configuration of the adsorbed layer although it has a comparatively small effect on the total amount of gelatin adsorbed. When the charge is the same as that on the surface, the proportion of adsorbed segments is small and the rate of desorption becomes significant     

Characterization of Poly(2-Hyoroxyethyl Methacrylate) Gels

Abstract

The crosslinking density and pore sizes of poly(2-hydroxyethyl methacrylate) (polyHEMA) hydrogels have been measured and correlated with the diffusion characteristics of a solute through the polymer. Studies indicated that diffusion is hindered both by obstruction by the polymer chains and by the immobility of the solvent within the gel. Values for the diffusion coefficient of a solute, D, and interaction parameters between the solvent and polymer suggest that as the concentration of crosslinking agent in the polymer network increases, the hydrophohicity of the polymer and the mobility of the solvent in the gel increase. Increased crosslinking however, increases the effectiveness of the obstruction effect, and the overall effect is a reduction in D.     

Gelatin Silver Halide Emulsion: A History

In 1850 Robert Bingham of England was the first to publish information about his invention — photographic plates containing a gelatin silver halide layer which produced negatives in a camera. The practicability of his procedure was confirmed in recent experiments.

The use of gelatin extends to the very beginning of the photographic negative-positive system which was invented by W. H. F. Talbot. Quantitative analyses have revealed that Talbot placed his coatings on paper bases which were heavily sized with gelatin.     

The Role and the Effect of Calcium Ion Content of Photographic Gelatins on Coating Defects

The influence of the calcium ion content of some photographic gelatins on the adhesion of gelatin solutions to emulsion layers was investigated by surface tension, pH and viscosity measurements and by coating using the dip method.

Adhesion of the gelatin layers was examined in the coating process under the following conditions:

Surface tension at varying wetting agent concentrations, for gelatin solutions which contain calcium ions from 0 to 5760 ppm concentration.

Surface tension at varying gelatin concentrations.

Surface tension at varying pH values of the gelatin solutions used in the coating process.

The experimental results demonstrate that, at gelatin concentrations between 2 and 4%, the adhesion ability of a gelatin solution on a dry or wet gelatin (emulsion) layer depends on the Ca2* content of the coating solution. It is necessary to have at least 1000 ppm Ca2* concentration to guarantee a perfect adhesion and a perfect coating. Gelatin source, pH and the viscosity of the system are unimportant.     

The Penetration of Solutes into Swollen Gel Layers

The times of penetration of 1M sodium thiosulphate and D163 developer at full strength and diluted were measured through gelatin coatings of 4.6, 10.5 and 20 nm dry thickness, with a thin underlayer of silver chloride emulsion as an indicator. The results show that the time of penetration is proportional to the product of the thickness of the swollen layer and the cube of the reciprocal of the proportion of water in the gel. For layers of gelatin of up to 20 gm, swollen to any extent of practical importance, the penetration is non-Fickian; the solute moves with constant velocity through the depth of the layer, presumably as a front of constant concentration gradient.