||The phenomena of the droplet impact play an important role on the semiconductor industry and the development of micro-electro-mechanical (MEM)system. The different patterns of droplet will be obtained when it is impacted at different parameters such as impact velocities, liquid dynamics viscosity, and substrate temperatures. The high-speed camera (CCD camera) with four hundred frames per second is used to observe and analyze these phenomena including the expansion (spreading), the flying (splashing), the turning back (recoil), the going upward (rebound), the concussion and the stability and so on. The temperature imposes on substrate at the value which is higher than the boiling temperature for water droplet case is also studied.|
The results indicate that the droplet impacts with different Weber number (We), the higher We number is, the higher spreading coefficient obtains. If the impact velocity increases, the droplet will be become the instability finger pattern. After that, droplet will be breakout if the impact velocity is higher. This means that when the We number increases, the droplet pattern changes from spreading to finger and splashing. Therefore, the phenomenon of splashing occurred in high We number, which is compare to spreading (180). For instance, when the We number is higher than 420, the splashing is observed for silicon oil case. When the substrate temperature changes, the splashing occurs only if the impact velocity is higher than those in case of lower temperature and the height of recoil is also different. The higher temperature is, the higher recoil obtains. For different liquids, we also observed the We number for the splashing phenomena occur in the water is higher than in the silicon oil. When the substrate temperature is higher than the liquid boiling temperature(110°C), we also observe that the water droplet is immediately rebound after impact on solid surface.
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