Abstract
The motion of droplets on a super-hydrophobic surface, whether by sliding or rolling, is a hot research topic. It affects the performance of super-hydrophobic materials in many industrial applications. In this study, a super-hydrophobic surface with a varied roughness is prepared by chemical-etching. The adhesive force of the advancing and receding contact angles for a droplet on a super-hydrophobic surface is characterized. The adhesive force increases with a decreased contact angle, and the minimum value is 0.0169 mN when the contact angle is 151.47°. At the same time, the motion of a droplet on the super-hydrophobic surface is investigated by using a high-speed camera and fluid software. The results show that the droplet rolls instead of sliding and the angular acceleration increases with an increased contact angle. The maximum value of the angular acceleration is 1,203.19 rad/s2 and this occurs when the contact angle is 151.47°. The relationship between the etching time, roughness, angular acceleration, and the adhesion force of the forward and backward contact angle are discussed.
Highlights
In the industrial field, there are several great potential applications of super-hydrophobic surfaces
In order to study the droplet motion on superhydrophobic surfaces, super-hydrophobic surfaces with a varied surface roughness were fabricated and the resistance force for rolling on the rough surfaces was evaluated
In the highly hydrophobic region, the resistance force for rolling decreased with an increasing contact angle, which is considered to be dependent on the surface roughness
Summary
There are several great potential applications of super-hydrophobic surfaces. Feng et al [38] prepared a super-hydrophobic surface on a carbon nanotube with a contact angle of 166° and a sliding angle of 3° for a water droplet They believed that an increased surface roughness and an enlarged air-liquid interface fraction led to a reduction in the wettability and decreased the adhesivity on the surface. Yao et al [29] fabricated a super-hydrophobic surface on silicon wafers They investigated different droplet sizes and the contact angle hysteresis impact on the rolling angle. Marmur et al [27] investigated the relationship between the main parameters for super-hydrophobicity They determined that the roll angle decreased along with the increase of contact angle. Based on a new theoretical model, the influence of the etching time on angular acceleration is discussed
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