Surfactant
From Silvergrain Research
A surfactant molecule has two major parts: a hydrophilic part and a hydrophobic part. The types of surfactants are classified by hydrophilic end of the molecule. However, the properties of hydrophobic end has a huge influence on the surfactant mechanism.
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Nonionic surfactants
Triton X-100
The most common surfactant of this category in darkroom use is Triton X-100 of Dow Chemicals (originally made by Union Carbide) and its equivalents from other chemical manufacturers. Octylphenol ethoxylate is one common generic name for this surfactant, among several other names. This surfactant is easy to use as a general purpose wetting agent, and it has been used widely as the final rinse solution in photography. However, this surfactant has a few shortcommings:
- estrogenic effects
Once discharged to sewer or the environment, this surfactant can be partially decomposed to octylphenol, a highly potent estrogenic compound to seriously disturb hormonal balance. A very tiny amount of this compound can cause serious problems to fish and other aquatic organisms. Long-term health effect of octylphenol ethoxylate to darkroom workers is unknown.
- poor biodegradability
This compound has very poor biodegradability and it is not effectively removed from wastewater.
- poor surfactant performance
Once it was considered good, but we have much better surfactants available from surfactant manufacturers.
- foaming property
As a use in final rinse solution, low foaming surfactant is more preferred. Triton X-100 is not particularly good in this aspect. There are other surfactants with lower foaming properties.
For these reasons, I have replaced Triton X-100 with other nonionic surfactants of superior surfactant properties, superior biodegradability and low toxicity.
Tergitol TMN-6
This is an excellent non-ionic surfactant, also from Dow (originally from Union Carbide) widely useful from emulsion coating to final rinse solution. However, this compound (branched secondary alcohol ethoxylate) is very poorly biodegradable and it should be used only when necessary, and only in the minimum required quantity. The surfactant performance of non-branched secondary alcohol ethoxylates and ethylene oxide ethoxylates may be significantly improved by blending TMN-6 in a very small quantity.
Plurafac SLF-18
Tergitol 15-s series
Tergitol L-62
Anionic surfactants
Triton X-200
A common anionic surfactant with low surface tension, suitable for high-speed emulsion coating. However, this surfactant produces a lot of stable foam, and it may not be suitable for foam-causing coating applications, such as brushing, spraying, etc.
Combination of silicone oil emulsion type defoaming agent is effective in reducing the foam. However, this causes another problem of coating defects due to defoamer. When foam is controlled by a defoamer, the performance as the coating aid may not be as good as some other surfactants that are inherently low in foaming.
Lodyne S-100
This is an amphoteric quaternary ammonium-acetate fluorosurfactant, commonly used in high speed emulsion coating. This surfactant, when used in about 100ppm concentration, decreases the surface tension to a very low level that most other surfactants can’t reach (below 20 dynes/cm). A combination with Triton X-200 or other similar surfactant is particularly effective.
This surfactant also produces stable foam.
Same active compound as Zonyl FSK and Masurf FS-330.
Demol N
Sodium salt of beta-naphthalene sulfonate formaldehyde condensate. This is an excellent dispersant and very useful for emulsion making, both as a dispersant as well as gelatin flocculating agent in the desalting process.
