Soap Film Evolution

The beautiful colors of a soap film reflect its variations in thickness. As a film drains and evaporates, it turns to shades of gray and black as it gets thinner. More than fifty years ago, one scientist proposed a free-energy-based explanation for how such ultrathin films might evolve. But it’s taken another half a century for experimental techniques to reach a point where the thickness of these ultrathin films could be measured well enough to test that theory. The new mechanism, known as spinodal stratification, has been observed in both vertical films (top) and foam (bottom) but has so far not been observed in any horizontal configuration, suggesting that buoyant effects are likely important, too. (Image and research credit: S. Yilixiati et al.; submitted by James S.)

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