Phenomena

Draining Soap Film

The brilliant colors of a soap film are directly related to the film’s thickness. Black regions, like the one in the upper right of this image, are the thinnest regions and may be less than 100 nanometers thick. (That’s smaller than the shortest wavelength of visible light!) The colors of the peacock-feather-like blooms along the bottom of the image demonstrate significant variations in film thickness. This is caused by uneven concentrations of surfactants in the film. The variations in concentration causes differences in local surface tension, which in turn moves fluid around within the film. This is known as a Marangoni effect. (Image credit: S. Berg and S. Troian)

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