Science Buddies: "Ask an Expert"

So I am doing an experiment where I mixed hand soap with dish detergent for one solution and bubble bath with dish detergent for another solution - same goes with water. I timed how long each bubble lasted, but the solutions with water lasted longer. I thought detergent has lower surface tension, which is needed to make bubbles, so I thought lower surface tension makes bubbles last longer. Is it because of water's specific heat, when it is trapped between two layers of soap molecules, which makes it evaporate more slowly in detergent?

Hi sw33tdr3amz,

That sounds like a really interesting experiment. There is a similar one on the Science Buddies site:

https://www.sciencebuddies.org/science- ... p025.shtml

I’m not quite clear on the solutions you are using, but I will try to help out. Please post again with a list of each solution you are testing. What is your control?

Soap formulations can be very complicated, especially those for hand soap and bubble bath, but my first thought is that hand soap, bubble bath, and dish detergent are all very similar. It is a good idea to think about what effect the water might be having on the bubble formation. I wonder if there is enough water in just the soap solutions (with no water added) to create the soap film structure that stabilizes bubbles and gives them the surface flexibility they need to form.

You can find some good information about soap films here:
https://en.m.wikipedia.org/wiki/Soap_film
http://www.arch.mcgill.ca/prof/sijpkes/ ... /final.htm

I would guess that adding water would allow the soap film structure to form, or form more uniformly. It is the soap layer barrier in the film structure that helps prevent the water from evaporating.

Let me know if that helps and if you have any more questions.

So my solutions are:
Detergent + Hand Soap
Detergent + Bubble Bath
Water + Hand Soap
Water + Bubble Bath
And in each solution, I used 2 tablespoons of each substance.

Thanks! Now I can see what you are comparing.

I suggest taking a close look at how the Bubble-ology experiment in my first post is organized. The basic bubble solution in that experiment is water and detergent. If you understand why those two ingredients are required in the basic solution, it might help you explain the results you are seeing.

Please also take a look at the explanation of variables here:
https://www.sciencebuddies.org/science- ... bles.shtml

If you choose to use detergent, hand soap, bubble bath, and water as your ingredients, make sure you have controlled and independent variables like in the Bubble-ology experiment.

Good luck and have fun!

I also have another question: since the detergent bubble solutions without water can create bubbles, does that mean that a layer of detergent is trapped between the soap layers, just like how a layer of water is between two soap layers?

Thank you for your help!

Hello again,

That's a very good question. Detergent/soap molecules (or surfactants) are very different than water molecules, so I would not expect them to take the place of water in a soap film. I have looked on the internet for ingredients lists for dish detergent, hand soap and bubble bath, and all of them list water as a main ingredient. I would guess that the water already included as an ingredient is helping to make the bubbles. It just might not be enough water to make the most stable, flexible film.

You are very welcome for the help. Let us know if you have more questions.