Department of Mechanical and Industrial Engineering, University of Massachusetts Amherst , 160 Governors Drive, Amherst, Massachusetts 01003-2210, United States.
Langmuir. 2016 Oct 11;32(40):10166-10176. doi: 10.1021/acs.langmuir.6b01994. Epub 2016 Sep 26.
In this study, the spreading and retraction dynamics of impacting droplets on lubricant-infused PTFE surfaces were investigated through high-speed imagery. Superhydrophobic Polytetrafluoroethylene (PTFE) surfaces with randomly rough microstructures were prepared by sanding PTFE. Several silicone oils with different viscosities were infused into the structures of superhydrophobic PTFE surfaces. A glycerin and water solution was used for the impacting droplets. The viscosity ratio between the impinging droplet and infused oil layer was varied from 0.06 to 1.2. The droplet impact dynamics on lubricant-infused surfaces were found to change as the viscosity of the infused silicone oil layer was decreased. These changes included an increase in the spreading rate of the droplet following impact, an increase to the maximum spreading diameter, and an increase to the retraction velocity after the droplet reached its maximum diameter. These variations in the impact dynamics were most significant as the viscosity ratio became larger than one and are likely due to the reduction of viscous losses between the oil and water phases during the spreading and retraction of the impacting droplet. Using a scaling analysis which takes into account the role of energy dissipation in the impact dynamics, all the data for the maximum diameter of the droplet on lubricant-infused PTFE surfaces were found to collapse onto a single master curve. Finally, measurements of the dynamic advancing and receding contact angle were made during spreading and retraction of the droplet. These measurements showed the expected Cox-Voinov-Tanner scaling of contact angle for the high oil viscosity, low viscosity ratio lubricant infused surfaces. However, like the superhydrophobic surface, little changes in either the dynamic advancing or receding contact angle were observed for droplets spreading on the surface infused with the lowest viscosity oil.
在这项研究中，通过高速成像研究了冲击液滴在注入润滑剂的聚四氟乙烯（PTFE）表面上的扩展和回缩动力学。通过磨砂聚四氟乙烯制备了具有随机粗糙微观结构的超疏水 PTFE 表面。将几种具有不同粘度的硅油注入超疏水 PTFE 表面的结构中。使用甘油和水溶液作为冲击液滴。冲击液滴和注入油层之间的粘度比从 0.06 变化到 1.2。发现润滑表面上的液滴冲击动力学随注入硅油层粘度的降低而发生变化。这些变化包括冲击后液滴扩展率的增加、最大扩展直径的增加以及液滴达到最大直径后回缩速度的增加。当粘度比大于 1 时，这些冲击动力学的变化最为显著，这可能是由于在冲击液滴扩展和回缩过程中油相和水相之间的粘性损失减少。使用考虑冲击动力学中能量耗散作用的标度分析，发现所有关于在注入润滑剂的 PTFE 表面上的液滴最大直径的数据都可以收敛到单个主曲线。最后，在液滴扩展和回缩过程中测量了动态前进和后退接触角。这些测量结果表明，对于高油粘度、低粘度比的润滑注入表面，接触角表现出预期的 Cox-Voinov-Tanner 标度。然而，就像超疏水表面一样，对于在注入最低粘度油的表面上扩展的液滴，观察到动态前进或后退接触角几乎没有变化。
