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Amazing liquid dynamics: Why do droplets bounce back like springs on superhydrophobic surfaces?
Liquid dynamics is the science that studies the movement and behavior of liquids. It involves many interesting phenomena, one of the most striking being the behavior of droplets when they impact surfaces. On superhydrophobic surfaces, droplets can rebound like springs. This result has attracted widespread attention from scientists and engineers. What is the principle that makes this phenomenon happen?
Physical process of droplet impact
When a droplet strikes a solid or liquid surface, its behavior is affected by many factors, including the droplet's size, velocity, surface tension, viscosity, and surface roughness. In general, when a droplet hits a dry solid surface, it usually expands on the surface and then shrinks again due to the influence of momentum. However, if the collision energy is high enough, the droplet's expansion may exceed its static contact angle limit, leading to various predictable consequences.
These results include different types of droplet deposition, splashing, rebounce and partial rebounce.
Droplet behavior on different surfaces
On dry solid surface
The behavior of droplets impinging on a dry solid surface is relatively simple: deposition is most common for small, low-velocity droplets. When hitting a rough surface, the "instant splash" effect is even more obvious. At this time, some additional tiny droplets will be generated near the droplet contact line. This phenomenon is called the formation of satellite droplets.
On superhydrophobic surface
On superhydrophobic surfaces, the performance of droplets is particularly amazing. According to research, small droplets can bounce off a solid surface more than 20 times before finally coming to rest. Key to this phenomenon is the time the droplet is in contact with the surface, which has important implications for applications such as heat transfer and aircraft icing.
These droplets exhibit an impressive ability to rebound during impact, and even the contact time after impact significantly affects their behavior.
Deformation pattern of droplets
The deformation pattern of a droplet upon impact can be divided according to the Weber number. When the Weber number is small, the deformation of the droplet is not significant; as the Weber number increases, the deformation of the droplet becomes more obvious, and even ripples are formed. When the Weber number reaches a certain level, the droplets may experience separation of satellite droplets. When the droplet is further compressed, an upward-squeezing liquid column is formed, which may result in complete rebound or partial rebound.
Behavior of droplets on wet surfaces
When a droplet hits an already wet surface, it behaves differently. If the speed of the droplet is below a certain critical value, the droplet will unfold and spread on the surface; if the speed exceeds the critical value, the impact of the droplet will cause splashing and may generate a strong shock wave. This phenomenon is especially obvious on thin liquid films, and the behavior of droplets is even more complex and changeable.
Behavior of droplets on liquid surface
When a droplet hits the surface of a liquid pool, it may float, bounce, merge, or splash. Floating droplets can remain on the liquid surface for several seconds, and the cleanliness of the surface plays an important role in this process. A higher Weber number will result in more splashing and may even cause central jets and splashes.
The impact behavior of droplets is not only a simple physical process, but also involves a very wide range of scientific topics. From water droplets in daily life to industrial applications, it has an impact that cannot be ignored.
Summary and Outlook
The behavior of droplets on different surfaces illustrates the fascinating world of liquid dynamics, from the phenomenon of bouncing on superhydrophobic surfaces to the hydrodynamic response after collision, which provides a new perspective on the behavior of liquids. . As technology advances, these phenomena may be applied to more fields, such as the design of self-cleaning materials or new heat exchangers. As we think about the behavior of these eye-catching liquids, and future scientific research will reveal more unknown mysteries, perhaps we should ask ourselves, how will these natural phenomena change the way we live?
