Combining water-repellence methods makes water bounce off surface

An anomalous phenomenon was observed by Doo Jin Lee and Young Seok Song from Department of Materials Science and Engineering of Seoul National University in South Korea. This anomaly was observed when two methods of water repellence were combined. Leidenfrost effect in combination with Cassie state made the water droplets bounce on the surface. And while sliding on the surface, or even levitating above it is ‘normal’, this bouncy anomaly may have impending implications for the future water repelling materials.

Leidenfrost effect is something we observe in the kitchen every now and then. When a surface is heated above Leidenfrost temperature (varying for different liquids of course) it won’t get wet, because the liquid will boil upon coming to contact with the surface, creating a vapor on which the liquid can then levitate. The German scientist discovered this back in 1756.

Cassie state on the other hand, relies on textured surfaces. If these are structured in a way that leaves enough space for air, the water will be supported by its high surface tension. In other words, if the surface is rough enough, the water will not get it wet. This hydrophobic property is characteristic of lotus plants. This property is copied on man made materials and widely used in various designs and installations.

In their study, the Lee and Song tested Leidenfrost effect on nanostructured Cassie surface and on a classic hydrophobic surface (achieved by fluorination). The results from the two surfaces varied significantly. The experiment was a lot more successful on the Cassie nanostructure than on its classic counterpart. The said bouncing only occurred on the nanosurface. “Our future work will focus on developing multiscale structures with microscale and nanoscale regularities, and explore the nonwetting characteristics of their surfaces with the dynamic Leidenfrost effect,” noted Doo Jin Lee in an interview.

Research in this area could be used to produce better materials for windows, paint, coating and windshields. This high water-repellent materials could save time cleaning windows, but also lives lost in traffic accidents during rainy days. The potential of these materials is immense and that is why more and more research is conducted in this area.