Wang Long-Zan, Zhou An, Zhou Jin-Zhi, Chen Longquan, Yu Ying-Song
Department of Mechanics, School of Civil Engineering, Architecture and Environment, Hubei University of Technology, Wuhan 430068, P. R. China.
Yangtze Delta Region Institute (Huzhou), University of Electronic Science and Technology of China, Huzhou 313001, P. R. China.
Soft Matter. 2021 Jun 28;17(24):5932-5940. doi: 10.1039/d1sm00354b. Epub 2021 May 27.
Droplet impact on pillar-arrayed polydimethylsiloxane (PDMS) surfaces with different solid fractions was studied. The lower and upper limits of Weber number, We, for complete rebound of impacting droplets decreased with decreasing solid fractions. Gaps were visible during the spreading and retraction processes of bouncing droplets on the surface with a solid fraction of 0.06 while no gaps were observed during the retraction process when We was greater than its upper limit, indicating that there existed a transition from the Cassie-Baxter wetting state to the Wenzel wetting state. Therefore, a novel model accounting for the penetration of a liquid into the cavities between the pillars was developed to predict the upper limit of the impact velocity of bouncing droplets. At high We, partial rebound was observed for surfaces with solid fractions of 0.50 and 0.20 while a sticky state was observed for the surface with a solid fraction of 0.06. Moreover, surface roughness has a great influence on the contact time of bouncing droplets. Besides, the maximum spreading parameter was found to follow a scaling law of We.
研究了液滴对具有不同固体分数的柱状排列聚二甲基硅氧烷（PDMS）表面的撞击。随着固体分数的降低，撞击液滴完全反弹的韦伯数（We）的下限和上限均降低。当固体分数为0.06时，在弹跳液滴在表面上的铺展和回缩过程中可见间隙，而当We大于其上限时，在回缩过程中未观察到间隙，这表明存在从Cassie-Baxter润湿状态到Wenzel润湿状态的转变。因此，开发了一种考虑液体渗透到柱之间空腔的新模型，以预测弹跳液滴撞击速度的上限。在高We时，对于固体分数为0.50和0.20的表面观察到部分反弹，而对于固体分数为0.06的表面观察到粘性状态。此外，表面粗糙度对弹跳液滴的接触时间有很大影响。此外，发现最大铺展参数遵循We的标度律。
