Bursting a Different Kind of Bubble
February 12, 2018
Spectacular Surface Tension: Marangoni Bursting
What's Going On Here?
Water, dye, oil, and alcohol: four simple ingredients are all it takes to create this amazing display of fluid dynamics! Placed on top of a bath of sunflower oil, dyed water will form a small droplike bead, because water molecules like to hang together—a property we call surface tension. Alcohol, on the other hand, has relatively low surface tension, so it's more inclined to spread out. But when we combine the two liquids, we see a marvelous merging of their behaviors!
Near the rim of the pool of dyed liquid, the alcohol evaporates more quickly than it does at the center, leaving behind a greater concentration of water. Because the water's surface tension is much higher than the alcohol's, this evaporation creates a region of relatively low surface tension at the center, with higher surface tension at the edges. This difference in surface tension is what drives the outward flow of the liquid, and as the alcohol evaporates, the water it leaves behind can bead up into the multitude of tiny droplets we see.
You can watch the full video at the American Physical Society's Gallery of Fluid Motion!