Theoretical and Experimental Studies on the Controllable Pancake Bouncing Behavior of Droplets

Abstract

A droplet that impacts on a superhydrophobic surface will undergo a process of unfolding, contracting, and finally rebounding from the surface. With regards to the pancake bouncing behavior of a droplet, since the retraction process of the droplet is omitted, the contact time is greatly shortened compared to the normal type of bouncing. However, the quantitative prediction to the range of droplet pancake bouncing and the adjustment of pancake bouncing state have yet to be probed into. In this paper, we reported the controllable pancake bouncing of droplets by adjusting the size of the superhydrophobic surface with microstructures. In addition, we also discovered a dimensional effect with regards to pancake bouncing, namely, the pancake bouncing would be more likely to happen on the surfaces with large post spacing for the droplet with the larger radius. The contact time could be reduced to 2 ms by adjusting the size of the microstructures and the radius of the droplets. Based on the relationship between the droplet bouncing state and the surface microstructure size, we are able to propose reasonable dimensions for the surfaces in order to control pancake bouncing.

Explosive Pancake Bouncing on Hot Superhydrophilic Surfaces

“…Shortly after impact, the droplet is suddenly levitated by its bursting vapor bubble from the surface at 1.75 ms, spreading to its maximum diameter in the air at 2.875 ms (Video S1, Supporting Information). This dynamic phenomenon is similar to pancake bouncing on superhydrophobic surfaces patterned with a square lattice of tapered posts. ,, However, in our work, the droplet bounces off on superhydrophilic surfaces before its complete spreading to the pancake shape, resulting in a further reduction of contact time. Thus, this special bouncing behavior is termed explosive pancake bouncing.…”

“…This dynamic phenomenon is similar to pancake bouncing on superhydrophobic surfaces patterned with a square lattice of tapered posts. 16,41,42 However, in our work, the droplet bounces off on superhydrophilic surfaces before its complete spreading to the pancake shape, resulting in a further reduction of contact time. Thus, this special bouncing behavior is termed explosive pancake bouncing.…”

Droplet motion on a wrinkled PDMS surface with a gradient structural length scale shorter than the droplet diameter

“…10 On the other hand, the partial wetting transition induces motion directed opposite to the wettability gradient because the Wenzel state induces strong contact line pinning compared with the Cassie-Baxter state 29 and it depends on the structural characteristics, impact velocity of the droplet and other parameters. 10,[30][31][32][33] However, in this study, a uniform wetting state is maintained during the bouncing because the direction of droplet motion follows the wettability characteristics and is assumed to be the Cassie-Baxter wetting state owing to the low impinging velocity. According to this, wetting transition can not explain the difference.…”

Facile fabrication of hierarchical textures for substrate-independent and durable superhydrophobic surfaces

“…4c shows the bouncing test of a water droplet on the treated glass surface. 52,53 When the water droplet just touched the treated surface, it was recorded as 0 ms. After coming in contact with the surface, the water droplet began to spread on the interface until the maximum diameter was reached in about 7 ms, then began to shrink, completed the contraction and gradually jumped up in about 16 ms. This is also a reflection of the superhydrophobicity and low adhesion of the treated surface (Movie S3 in the ESI †).…”