Diverse Applications of Surface and Colloid Chemistry in Science and Industry - Surface and Colloid Chemistry: Principles and Applications - page 225

These colloidals are dispersed in aqueous media, and exhibit twofold progenies:
polymers and colloidals.
10.5.2.1.1 Photographic Industry (Emulsion Films)
Photographic film production has been a very sophisticated technical innovation.
In general, the photographic film consists of a sheet of plastic base (polyester or
nitrocellulose [celluloid]) that is coated with a very thin emulsion containing light-
sensitive Ag salts. The latter is bonded to gelatine gel. The film is exposed to an
image created by the lens. The resolution of the image produced is determined by the
size of the Ag particles. Most of the industry is prone to high secrecy, and not much
is known about how the different producers of film achieve the end result. Black-and-
white films were much simpler than color films. In color films, the emulsion con-
sisted of three different color layers. Each was developed separately after exposure.
It is obvious that the demand of making such a film is very complex. Further, the
chemical reactions that take place on the surface of the film may vary from minutes
(or longer) to merely 1/1000 s. This, indeed, demands much technology knowhow.
Therefore, not only are their production techniques safeguarded by patents but there
is also a large degree of secrecy at the production sites.
Making photographic gelatin: Photographic gelatins have a suspension of silver
halide salts that are sensitive to light. When they are still warm, these gelatins are
spread on a transparent plastic film to obtain a photographic film, or on a card to
obtain a surface for photographic prints. As shown in the history of photography,
there are many methods to produce photosensitive surfaces, and many of them do
not use silver salts.
10.5.2.1.2 Diverse Applications of Foams
Even though Foam formation is a simple process (i.e., blowing air into a solution of
a surface-active agent in water), its applications are far too involved, especially in
those cases where foam is the main characteristic of the end product. Some useful
examples are discussed in the following text.
Fireighting : Most firefighting begins with water; however, water alone, in many
cases, is not efficient due to several limitations. The main approach is to contain the
fire by covering the flames with a layer of foam so that their contact with air (i.e.,
oxygen) is prevented. In the case of the application of foams in firefighting, the rate
of drainage must be considered. The foam firefighting procedure is useful since it
gives slower evaporation and thus better results. The thick foam also helps in reduc-
ing the vapors (of organic fluids).
Diverse foam structure applications : In foam rubber, foamed polymers, shaving
foams, milk shakes, and whipped creams, slowly draining thin liquid films (TLF)
are needed. Accordingly, the rate of drainage is the most important factor in such
industrial foam applications.
10.5.2.2 medical care and Surface chemistry
Injury to any part of the human body leads to blood loss, and in general, healing
requires fast clotting in order to reduce excess loss. Each soldier in the U.S. army
carries a sponge or powder that contains clotting agents. These treatments are found