How do bubbles in fizzy drinks get attracted to the walls and bottom of a cup?

[Chen]

Hello,

In this article:

http://www.deas.harvard.edu/softmat/downloads/2005-13.pdf (PDF, 175kb)

The authors give a simplifed explanation of why a bubble is attracted to the walls at the surface of the liquid. I can definitely understand this explanation, but my question is why do bubbles get attracted to the walls even below the surface? If you fill a glass with some coke (or any other fizzy drink) you will notice that a great deal of bubbles are not floating to the surface of the drink, but instead they are firmly attached to the walls of the cup. Furthermore, you can also notice bubbles attached to the bottom end of the cup! This is very counter intuitive, at least for me.

So I would like to know how you can explain the phenomenon of air bubbles that get attached to the submerged part of the walls of the cup, and even to its very bottom.

Thanks,
Chen

 

[rtharbaugh1]

Hi Chen

I seem to recall that bubbles need an irregularity on which to form. They won't form on perfectly smooth surfaces. The bubbles that form on the sides and bottom of the glass are actually forming on tiny scratches, dust motes, bits of stuff that did not come off in the last wash.

I hope someone here can give you a more technical answer.

R.

 

[DaveC426913]

rtharbaugh1 is correct. The bubbles are not attracted to the walls, they are formed there.

 

[Chen]

Okay, so the bubbles are formed on the walls - but why do they stay there post formation? Their are obviously lighter than the liquid, so shouldn't they shoot up to the surface?

By the way, if you know of a good website or book that teaches about the basics of surface tension, I'd be grateful.
Would it be correct to say that surface tension is the result of the liquid trying to minimalize its surface area? Is this always the case?

Thanks!
Chen

 

[DaveC426913]

Because they won't detach from the surface where they form until they get large enough that the bouyancy overcomes the natural "stickiness". (It's that stickiness that's causing the bubbles to form there in the first place).

 

[rtharbaugh1]

Would it be correct to say that surface tension is the result of the liquid trying to minimalize its surface area? Is this always the case?

Thanks!
Chen

I think not. Liquid doesn't try to do anything...it just does what it has to do. This gramatical form is very common, saying that nature abhors a vacuum and so on, but it is really a sloppy way of thinking about things, and is likely to mislead you. You might be better off making it a general rule never to attribute motives to inanimate objects.

Instead, think in terms of the forces that are at work. Surface tension acts to minimize surface area. I think it is fair to say that this is always the case. But there are complicating situations. The surface of water in a tube does not take a minimal geometric cross section of the tube, but instead has a curved shape called a meniscus, if I remember the spelling. This shape has to do with the difference in the attraction of water to glass compared to its attraction to itself.

R

 

[Clausius2]

By the way, if you know of a good website or book that teaches about the basics of surface tension, I'd be grateful.

Gennes, "Capillarity and wetting phenomena". Springer Verlag.

I recommend this book of Gennes who got the nobel prize. Also go to Mech and Aero engineering forum here and click on the thread of experimental fluid mechanics videos. There you'll find a wonderful lesson on surface tension in the lab.