Colourful kaleidoscope of soap bubbles

The whirling hues on the surface of bubbles is caused in part by the Marangoni effect, a phenomenon that occurs when molecules called surfactants move from areas of low surface tension to areas of higher surface tension along the boundary between two different substances.

Stanford University researchers created an air bubble, around a millimetre across, under the surface of a soapy solution, raising the bubble quickly to the surface, pausing and then raising it again.

With each bump upward, they launched a new layer of Marangoni flows at the outer rim of the bubble, which trapped the previous layer. They were able to create as many as seven different Marangoni flows in one bubble.

The work was published in Physics Review Fluids.