Surface tension of ethanol solution?

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SUMMARY

The discussion centers on the challenges of reducing surface tension in a 75% ethanol (EtOH) and 25% water (H2O) solution to eliminate floating debris during microscopic examination. Jonathan, the inquirer, has experimented with various surfactants, including "Cascade," Kodak PhotoFlo, and detergents, but none have proven effective. The conversation highlights that the surface tension of ethanol is lower than that of water due to the molecular structure and bonding differences, suggesting that increasing ethanol concentration may be a potential solution, although it risks damaging museum specimens.

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  • Understanding of surface tension and its molecular basis
  • Familiarity with ethanol and water mixtures
  • Knowledge of surfactants and their properties
  • Experience with microscopy techniques, particularly stereomicroscopy
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Researchers, microscopists, and conservators working with biological specimens in ethanol solutions, particularly those seeking to optimize viewing conditions and minimize contamination in microscopy.

Ogulnius
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A query about, I think, extinguishing surface tension in 75% EtOH:H2O.
I need to examine microscopically (~50x) specimens preserved and stored in the above medium, which I do by immersing them in dishes filled with the above, illuminating w fiber optics, and examining with a stereomicroscope.
I notice that when filling the dish for the first time, inevitably a floating "island" of crud appears (technical term for dust, grit, fibers, skin particles, who knows). Would like to get rid of it by a more elegant means than dragging a bit of lens paper across the surface of the alcohol:water mixture. So,
1. Can you add something (surfactant?) to 75 EtOH: 25 H2O to cut surface tension enough that said island sinks. Have tried several commercially available surfactants, "Cascade," Kodak PhotoFlo, detergent, none work. Is the surface tension of Ethanol all that different from water?
2. Out of curiosity, why does the island always come to rest centered on (and thus ruining) the field of view? I assume it has something to do with having fiber optic lights trained on the specimen (width ca. 2mm), and the heat convection patterns of a fluid in a round dish, but would like a more exact explanation.
thanks in advance,
Jonathan
 
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The surface tension is a result of the O-H bonds of the molecules interacting with each other. The O-H in ethanol is similar to an O-H in H20 but ethanol only has one and the molecule is also larger in size so the cohesion is not as efficient. Water has considerably greater surface tension.

I don't know what you're trying to view but one idea might be to increase the concentration of ethanol vs water if possible.
 
Thanks! That makes sense, but if so, you'd think surfactants in 75% EtOH would have about the same effects they do in water. But, as near as I can tell, they don't. The solution has to stay at about 75% because these are museum specimens, and anything over say 90% will dehydrate the tissues and lead to damage.