Jan 11 2009
the iridescent spherical film
Soap bubbles are inherently cool. My daughter thinks so, anyway. She keeps pointing at the bottle of bubble liquid and going “mmm … mmm …” until we pick it up and blow some bubbles.
The miracle of the soap bubble comes from the surface tension of water, decreased but stabilised by the soap — via the Marangoni effect, where the soap goes wherever in the bubble it’s needed. The iridescence comes from the thickness of the film (800 nanometres) being comparable to the wavelength of light (340 to 760 nanometres).
The bit I haven’t managed to find an explanation of is how to make them more stable. The bubble liquid has run out so we topped it up with washing-up liquid, which doesn’t make bubbles nearly as well, and certainly not streams of them. Perhaps if we use more concentrated liquid, that’ll work.
Photo: “Soap bubble” by Raphael Quinet. Taken in Nandrin, Liege, Belgium on 24 June 2007 on a Nikon D70. CC by-sa 2.0.
There are people in this world who care about their bubbles, and have figured out what brand of dish detergent works best and at what dilution and so on. I am not one of these people, but I used to own a book written by them on the subject. Whose identifying information I’ve forgotten. But, the knowledge is out there.
There’s probably a wiki about it.