What is the effect of a square transparent rectangle on the meniscus in a tube?

[Helphelphelp]

Hi,
I was wondering about the meniscus we get in a round tube, like a test tube or a boiling tube, or even a classic measuring cylinder. If we have a square transparent rectangle with water in - would this at all reduce the effect of the meniscus?
How else is the effect of the meniscus reduced? I have been researching it and it suggested by putting it in a water bath.
Does the material affect it? I know mercury inverts the meniscus, but is there any known substance which gives a flat reading?
Thank you so much, even if you could just answer anyone of these it's really appreciated :)

 

[berkeman]

Hi,
I was wondering about the meniscus we get in a round tube, like a test tube or a boiling tube, or even a classic measuring cylinder. If we have a square transparent rectangle with water in - would this at all reduce the effect of the meniscus?
How else is the effect of the meniscus reduced? I have been researching it and it suggested by putting it in a water bath.
Does the material affect it? I know mercury inverts the meniscus, but is there any known substance which gives a flat reading?
Thank you so much, even if you could just answer anyone of these it's really appreciated :)

With a little Google searching, I found that the choice of the tube's material can give you a flat water meniscus. Search down this page for "meniscus"

http://www.visionlearning.com/en/library/Chemistry/1/Properties-of-Liquids/222

Adhesion
Adhesion is the tendency of a compound to interact with another compound. (Remember that, in contrast, cohesion is the tendency of a compound to interact with itself.) Adhesion helps explain how liquids interact with their containers and with other liquids.

One example of an interaction with high adhesion is that between water and glass. Both water and glass are held together by polar [verb] To hold or fasten units such as atoms or... read more " title="" style="box-sizing: border-box; color: rgb(48, 110, 43); padding: 4px 2px; white-space: nowrap;">bonds. Therefore, the two materials can also form favorable polar interactions with each other, leading to high adhesion. You may have even seen these attractive adhesive forces in action in lab. When water is in a glass graduated cylinder, for example, the water creeps up the sides of the glass, creating a concave curve at the top called a meniscus, as shown in the figure below. Water in graduated cylinders made out of some types of non-polar plastic, on the other hand, forms a flat meniscus because there are neither attractive nor repellant cohesive forces between the water and the plastic. (See Figure 8 for a comparison of polar and non-polar graduated cylinders.)

 

[Andy Resnick]

If we have a square transparent rectangle with water in - would this at all reduce the effect of the meniscus?

That's an interesting question. The physical quantity that matters is the curvature of the fluid-fluid interface because that's the energy of the surface, which is minimized. In the vicinity of the corners, if the corners are sufficiently square (say, the inside corners of a proper cuvette), the curvature can be sufficiently high as to interfere with wetting (movement of the solid-fluid-fluid contact line), leading to changes in the contact angle in the vicinity of the inside corner. As I recall, if the liquid wets the glass, the liquid is 'wicked' up the interior corners, so I suspect the opposite occurs when the fluid does not wet the glass.

http://pubs.rsc.org/services/images...e/2015/CC/c5cc01480h/c5cc01480h-f1_hi-res.gif

It's easy to check- I'll try and remember to try this when I get back in the lab (in a week).

About your other question- the contact angle can be (somewhat) controlled- that is, it's easy to make a surface wetting or nonwetting for (say) water, but it's not so simple to make a surface that water forms a contact angle at a specified angle.

http://pubs.rsc.org/services/images...cleimage/2011/LC/c1lc20388f/c1lc20388f-f6.gif

Pickering emulsions have solid particles pinned at a fluid-fluid interface, in some cases the contact angle is 90 degrees, but I don't know the secret recipe.