Surface tension of ethanol solution?

In summary, the individual is seeking a way to get rid of floating debris in a 75% ethanol:water mixture used to preserve and examine specimens under a microscope. They have tried using various surfactants but none have been effective. They also have a curiosity about why the debris always comes to rest in the center of the field of view. The expert suggests increasing the concentration of ethanol, but the individual mentions that it cannot go above 90% without damaging the specimens.
  • #1
Ogulnius
18
0
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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  • #2
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.
 
  • #3
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.
 

FAQ: Surface tension of ethanol solution?

1. What is surface tension?

Surface tension is a physical property of liquids that describes the force acting on the surface of the liquid, causing it to behave as if it has a thin elastic film. It is the result of the cohesive forces between the molecules at the surface of the liquid.

2. How is surface tension measured?

Surface tension is usually measured in units of force per unit length, such as newtons per meter (N/m). It can be measured using various methods, such as the drop weight method, the capillary rise method, or the Du Nouy ring method.

3. How does the surface tension of ethanol solution differ from pure ethanol?

The surface tension of a liquid is affected by the presence of solutes. In the case of an ethanol solution, the surface tension will decrease as the concentration of ethanol increases. This is due to the interactions between the ethanol molecules and the solvent molecules, which disrupt the cohesive forces at the surface.

4. What factors affect the surface tension of an ethanol solution?

The surface tension of an ethanol solution can be affected by various factors, such as temperature, concentration, and the presence of other solutes. Generally, as the temperature increases, the surface tension decreases. Higher concentrations of ethanol will also result in a lower surface tension. Other solutes, such as salts, can also affect the surface tension.

5. Why is the surface tension of ethanol solution important?

The surface tension of a liquid plays an important role in many natural and industrial processes. In the case of ethanol solutions, it can affect the absorption and distribution of the solution in biological systems, as well as the formation and stability of foams and emulsions. It is also an important factor in determining the physical properties and behavior of the solution in industrial processes, such as distillation and chromatography.

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