Water droplets "walking" on oil film, this is not science fiction! The secret of water droplets "dancing"

Author: Duan Yuechu

Water droplets dancing on a thin oil film? It sounds like a scene from a science fiction movie, but in fact, scientists have observed this amazing phenomenon in the laboratory. The study was conducted by Professor Dan Daniel and his colleagues at King Abdullah University of Science and Technology in Saudi Arabia. They found that when water droplets condense on a thin oil film coated with a pattern of micron-sized pillars, they exhibit surprising collective motion.

The steps for this experiment are simple. The researchers first coated a silicon surface with a thin film of oil and etched it with a pattern of micrometer-sized pillars. Then, they cooled the film to 4 degrees Celsius. Soon after, water droplets began to condense on the film and gradually moved closer. After about 25 minutes, the largest droplets began to dance, moving like a snake in a series of self-avoiding bending motions and then turning in circles. This motion continued to switch between snakes and circles for about 4 hours until the droplets stopped dancing.

What is the principle behind this phenomenon? Daniel and his colleagues calculated that the energy released by the continuous fusion of large droplets with much smaller droplets is sufficient to drive this motion. In addition, the redistribution of oil caused by the dancing oil droplets leads to the switch between serpentine and circular dynamics.

Where might this research be applied? First, this phenomenon has important applications in heat transfer and water collection. In addition, this research provides us with a window to understand active matter systems in nature. There are many similar systems in nature, from swarms of bacteria to flocks of birds. These systems have components that consume energy to move or exert force. In the laboratory, creating such an active matter system usually requires a complex setup and components that can convert light, biochemical energy, or chemical energy into motion. This research provides us with a simple physical system that may help us further explore and study active matter systems.

Through this research, we can see that the wonderful phenomena in nature are everywhere, as long as we discover and explore them with our heart. At the same time, this also shows the spirit of scientists to pursue the truth and reveal the mysteries of nature. In the future, I believe that this research will have a wide range of applications in many fields and bring more surprises to mankind.

References:

Physics - Droplets Dance After They Merge https://physics.aps.org/articles/v17/s15