Thermal Marangoni bubbles.

When air reaches the surface of a pool (or bath) of pure liquid, it does not form long-lasting bubbles, as opposed to when the bath contains surfactants. Here we describe what happens when the pool is pure (consisting of oil), yet hot. The bubbles dwelling at the surface can then live for minutes or even longer, which we interpret as a consequence of the gradients of temperature generated in this experiment. Indeed, oil is observed to be constantly drawn to the apex of the bubble, which opposes its gravitational drainage. Since their existence relies on ascending Marangoni flows, thermal bubbles are found to be dynamical in essence, which endows the oil film with remarkable stability and persistence.