Submerged Meniscus?

[NathanUT]

I am teaching density in my 5th grade science class and came across an intriguing question. We made a density column and noticed something interesting. The top layer of our density column is isopropyl alcohol colored blue. The layer just beneath it is some vegetable oil. What we noticed is all the layers separated in a flat line... except the blue alcohol. It dipped down into the oil layer as though filling a bowl. I speculated to myself that this might be the result of the oil bonding easier with the graduated cylinder than itself, causing a meniscus, and the less dense alcohol just filled in the space. Is this what's happening? Can there be a submerged meniscus? Actually, I know there can be (ocean layers separated by density differences in temperature and salinity are certainly not always flat), I'm just wondering if that's what's happening in this case. One of my students noticed the same thing, so we discussed & I asked the class for ideas. I was really impressed that one student also wondered if it was a meniscus. Whether we're right or not, I complimented her on thinking like a scientist. So cool! But I promised the class I would research it & try to give them a definitive answer. Little help?!

[Mr Skeptic]

Yes, you can have a submerged meniscus. The principle is very similar (well the same really). For a regular meniscus, you compare the attraction of the liquid to the walls to the attraction of the liquid to itself. The meniscus can curve either upward or downward.

 

If you have two liquids, you also need to consider the attraction of both liquids to the walls and the liquids to each other (presumably not very strong since they are immiscible) and to themselves. I think the liquid that would have a sharper meniscus in air would win (but it would be an upside down meniscus if that layer is on top). Don't quote me on that though.

[NathanUT]

Yes, you can have a submerged meniscus. The principle is very similar (well the same really). For a regular meniscus, you compare the attraction of the liquid to the walls to the attraction of the liquid to itself. The meniscus can curve either upward or downward.

 

If you have two liquids, you also need to consider the attraction of both liquids to the walls and the liquids to each other (presumably not very strong since they are immiscible) and to themselves. I think the liquid that would have a sharper meniscus in air would win (but it would be an upside down meniscus if that layer is on top). Don't quote me on that though.

 

That's pretty much what I was thinking, I just wanted to get at least some confirmation before I taught it to my kids. Thanks so much for responding!