Soap Bubbles
How do soap bubbles form?
The internet says soap weakens the surface tension of water when it is added in to the water, but how does that help with making soap bubbles? I read the wikipedia and I still do not get it, can anyone explain this to me please?
A soap molecule has a water-loving end and a oil-loving end (they don’t like to mix). Imagine this as a long molecular “stick” that is larger than a water molecule (not immensely larger).
Typically the soap will probably jumble around until it finds the lowest energy position. In a bubble, the soap molecules will move toward the surface (both inside and outside). This is because the oil end does not want to be in the water so it juts out into the air.
The following page sort of hints at the explanation. I’ll try to summarize it here, but what I described in the above text is in a picture at the bottom of the link below (shows oil tails sticking out of the surface)
http://www.exploratorium.edu/ronh/bubbles/soap.html
Here is the key issue, water has a high surface tension. Normally, adding the soap into the water lowers the surface tension because these long soap molecules prevent water molecules from reaching the surface. If I understand correctly, in the case of a soap bubble the oil ends are getting in the way of water because they are trying to get out of the bubble skin (like that picture on the above website). If you stretch the bubble skin (increase the surface area), then the soap molecules (clustered at the surface) spread out, allowing room for water molecules, and increasing surface tension.
Now think of this, the more you stretch the bubble, the more force it supplies. This is sort of like a balloon membrane. Tension along the surface of the bubble increases as you stretch it, so it naturally wants to shrink to minimize energy. Once the bubble shrinks, the soap molecules hit a critical saturation and the surface tension lowers so that it can’t shrink the bubble any more.
Giant Stinson Beach Bubbles (Canon 550D)
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