Stability Beyond Surfactants: The Remarkable Life of Thermal Marangoni Bubbles*

Free-standing films are inherently fragile, unless stabilized with surfactants. Similarly, air bubbles on the surface of a pure liquid are ephemeral, which leads to the intriguing question: Can air bubbles be stabilized in the absence of surfactants? In pursuit of an answer, we discovered a compelling scenario – a pure, hot oil pool where bubbles at the surface exhibited surprisingly extended lifespans, lasting for tens of minutes or more. We attribute this remarkable longevity to the temperature gradients generated in this experiment. Indeed, oil was observed to be constantly drawn to the apex of the bubble, opposing its gravitational drainage. To investigate further, we developed a subtle measurement technique to quantify the ascending Marangoni flows. Our findings shed light on the mechanism behind the remarkable stability and persistence of thermal Marangoni bubbles, that is, how 'Marangoni' does not let bubbles die 'Young'...