超疏水動態表面上液滴側向彈跳之研究

Abstract

水滴對表面的影響涉及複雜的物理機制。根據具體條件，水滴對表面的影響可能表現為沉積、沸騰、飛濺和彈跳行為。儘管現在對靜止超疏水錶面的影響進行了廣泛的研究，但對液滴對旋轉超疏水錶面的影響行為的理解仍然有限。因此本研究希望透過設計不同超疏水表面，並且以不同狀態與液滴發生碰撞，找出表面與液滴交互作用最小的狀態。 本研究採用聚二甲基矽氧烷 (PDMS) 作為固態基質表面，透過調整雷射掃描參數使 PDMS 表面具有不同起伏的二氧化矽微結構，使其表面性質呈現超疏水，再將液滴以自由落體的形式撞擊表面。當PDMS以不同功率燒蝕時，會有不同起伏結構，也會有不同濕潤性。當液滴撞擊靜態表面時，發現結構大小會影響液滴彈跳形式，進而影響液滴反彈高度恢復係數、接觸時間。接著觀察液滴撞擊旋轉表面中心，我們發現液滴撞擊旋轉表面中心時，液滴和表面接觸時間較液滴撞擊靜態表面減少，液滴在動態表面彈跳恢復係數較高。當液滴撞擊旋轉表面偏心處時，液滴會沿著旋轉切線飛濺出去，隨著表面起伏和遲滯、表面轉速和墜落高度改變，液滴會有不同變形量，導致液滴會有不同的運動型態飛濺出去，進而影響液滴橫向速度和彈跳恢復係數。 本研究透過設計不同微結構的超關注PDMS表面，探討靜止在靜態與旋轉表面上的碰撞行為，發現表面結構、旋轉速度與碰撞位置對碰撞的接觸時間、反彈恢復係數及運動的顯著影響。

Droplet interactions with surfaces involve complex physical mechanisms. Depending on specific conditions, droplet behavior upon impacting a surface can manifest as deposition, boiling, splashing, or bouncing. While extensive research has been conducted on the effects of droplets on stationary superhydrophobic surfaces, understanding of droplet behavior on rotating superhydrophobic surfaces remains limited. Therefore, this study aims to identify the conditions under which the interaction between the surface and the droplet is minimized by designing various superhydrophobic surfaces and investigating their collisions with droplets under different conditions. In this study, polydimethylsiloxane (PDMS) was used as the solid substrate surface. By adjusting laser scanning parameters, silica microstructures with different roughness were fabricated on the PDMS surface, rendering it superhydrophobic. Droplets were then allowed to collide with the surface in free-fall form. When the PDMS surface was ablated at different power levels, varying roughness structures and wettability were observed. During droplet impact on a static surface, it was found that the size of the surface structures influenced the droplet's bouncing behavior, which in turn affected the droplet rebound height recovery coefficient and contact time.Next, droplet impact at the center of a rotating surface was observed. The results showed that the contact time between the droplet and the surface was shorter compared to that on a static surface, and the rebound height recovery coefficient was higher on the dynamic surface.When droplets impacted the eccentric region of a rotating surface, they splashed outward along the tangential direction of rotation. With changes in surface roughness, hysteresis, rotational speed, and drop height, droplets exhibited varying deformation, leading to different motion patterns during splashing. These variations ultimately affected the droplet's lateral velocity and rebound height recovery coefficient. This study designed superhydrophobic PDMS surfaces with different microstructures to investigate droplet impact behavior on static and rotating surfaces. It was found that surface structure, rotational speed, and impact position significantly influence the contact time, restitution coefficient, and motion.