View Full Version : Making Spy Film, Microdots

Mustafa Umut Sarac
11-24-2012, 02:48 PM
When I was researching on nanoparticles in emulsions , I found that at Ilford Site.

Although the silver halide crystals in ordinary photographic materials are around one micron across, much smaller crystals can be made where necessary.
Many people have heard of “microdots” – photographic transparencies the size of a full stop, used to transmit documents secretly. These are not a myth; they were actually used by spies during the 20th century. In order to put a readable image of a large document into such a small area, special photographic emulsions were needed, with crystal sizes around 50 nanometres.
The area in which nanosized emulsions are required nowadays is holography. Modern holographic materials contain crystals around 30 nanometres or less in diameter.
To make such crystals, it is necessary to use conditions which allow crystal formation (nucleation) but effectively prevent crystal growth. These may include low concentrations of reactants, low temperatures, and very precise control throughout.

I am thinking that nanotechnology advanced too far and finding everykind of nanopparticles are easy.

How can We match silver nanoparticles in to emulsion making ?

PE ?

11-24-2012, 03:31 PM
I always understood emulsionmaking as nanotechnology. Just the term was not invented back then.

Emulsionmaking is still a bulk businees. Certain technologies are just too expensive for this.
And not everything nano makes sense. It may be hip but not useful.

Mustafa Umut Sarac
11-24-2012, 05:30 PM
Characterization of AgBr/I nanoparticles prepared in fish gelatin : Silver halide science and technology

Department of Applied Chemistry, University of Science and Technology of China, Hefei, Anhui, CHINE
(2) Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, CHINE

The photographic emulsions, which consist of suspensions of silver iodobromide nanoparticles in fish gelatin, were made by a double-jet method. The average sizes of the particles obtained by XRD measurement and TEM observation were 16 nm and 14.3 nm, respectively. The microwave photoconductivity measurement showed two first-order kinetic processes. The electron lifetime in the first process shortened obviously, indicating a mass of shallow traps on the nanoparticle surfaces. The second process was a slower decay one, which was considered as electron trapping followed by the reaction of trapped electrons with interstitial silver ions. A higher maximum frequency obtained in the dielectric loss measurement indicated formation of interstitial silver ions with high concentration on the surfaces of the nanoparticles. For sulfur sensitized nanoparticle emulsion, sensitivity and gamma increased with increase of both amount of sulfur sensitizer and sensitizing time, but the excessive amount of sulfur sensitizer rapidly led to the occurrence of additive fog density. In the case of the optimum sensitivity and gamma, sulfur sensitization centers, i.e., dimers of Ag2S on the AgBr/I nanoparticle surface can be roughly estimated as no more than 500. The addition of methionine (Met) and methionine sulfoxide (Metsox) in the emulsion at chemical ripening made the density-(log exposure) curves shifted to lower exposure which demonstrated that their effective sensitization attributed to the bromine acceptance and to reducing the power of these additive

Mustafa Umut Sarac
11-24-2012, 05:33 PM
Investigation on nanocrystallite silver halide photographic emulsion


The AgBr/l nanocrystallite photographic emulsions containing different iodide values are prepared with complexing precipitation at a homogeneous phase The average sizes of the particles in the enulsions are from 14 to 30 nm. The size and the shape of the nanocrystallite are detected by transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. Because of the high surface activity of the nanoparticle, the emulsion has a lower sensitivity and more fog. When the lodine coment increases to 11 The emulsion shows the highest sensitivity Sulphur sensitization has little effect on this kind of emulsion but gold sensitization scems to be effective.

Mustafa Umut Sarac
11-24-2012, 05:48 PM
I think this is what we use today. Above post article particles 5 to 100 times smaller.

Light absorption properties of monodispersed micron/nano-sized silver halide emulsions : Cubic silver halide and AgCl {100} T-grain

LI Zhi ; ZHENG Tong ; PENG Bi-Xian ; ...

A silver chloride {100} T-grain emulsion and a series of cubic silver halide emulsions were prepared by varying the parameters correctly during nucleation and growing processes of grains. After the observation of SEM and TEM, following statistical data were obtained: the diameters of the cubic microcrystal are 80, 150, 600 nm respectively, the equivalent circular diameter (ECD) of the {100} tabular microcrystal is 1400 nm and the shape ratio (ratio of ECD to thickness of a grain) is not less than 7. The absorbencies and the relative absorbed energy of the emulsions were calculated and then compared with each other. It can be easily found that the nano-sized AgX microcrystal retained the high light absorption in visible light region and obtained a red shift of its peak, and the absorbance of the AgCl {100} T-grain emulsion was also particular.