# Half life measurements on foams

1. Aug 11, 2004

### Telmerk

Hi!
I'd like to make some half-life measurements on water based foams. I have only simple instruments for it. Can anybody help me? I don't know the exact method that how to make this measurement correctly. And I also need the mathematical apparatus for it. I've found an article where the authors say that a dry foam decays logarithmically. Please help me if you know a method of measuring it accurately! Thanks a lot in advance!

2. Aug 11, 2004

### brewnog

How dense are these foams? Could you contain them in some kind of weak-skinned balloon, and measure and record the amount of air which leaves the balloon (which will be almost equal to the volumetric change due to bubble collapse). The half life is merely the time it takes for the number of bubbles (approximated by the volume of your sample) to halve. Let me know if I got the wrong end of the stick, or even the wrong stick!

3. Aug 11, 2004

### Telmerk

Hello! These are aqueous foams(water+nitrogen), so their density is very low. They're dry, that means they don't contain large amount of water. Half life in this case means the time elapsed when the foam reaches its half of its initial height. The problem is that I cannot measure accurately the height of the foam, because it is uncertain, and calculating an average adds too big mistakes to the measurement.
Well, measuring the amount of gas would be good, but unfortunately I don't know how to do this properly. . .

4. Aug 11, 2004

### brewnog

Here's my plan!

Obtain a see through plastic container which is fairly large. The wider this is, the more accurate your results will be. Mark volumetric graduations onto the side of the container, (use water for this). Ideally you want to suspend a film of thin, air-permeable fabric (perhaps a cotton gauze, filter paper, you get the idea) on the top of the foam stack. If the foam is not dense enough for this, just use the biggest container you can find, then any variations in the height of the stack should begin to cancel each other out. I would still recommend you use a system of averages, there is no reason at all why this would add mistakes to your results.

5. Aug 12, 2004

### Telmerk

Thanks, Brewnog! This is what I'm doing now! I have not tried the filter aper yet, but I may be. The accuracy of my measurements is about 0.5-1 cm, due to the inhomogenity of the foam height. The height of the liquid must change, too, during the experiment, but I cannot notice it, because my container has a quite large cross section (8x12cm).