State Key Laboratory of Fluid Power & Mechatronic Systems , Zhejiang University , 38 Zheda Road , Hangzhou 310027 , China.
Langmuir. 2018 Apr 17;34(15):4484-4493. doi: 10.1021/acs.langmuir.8b00172. Epub 2018 Apr 5.
Liquids confined between two parallel plates can perform the function of transmission, support, or lubrication in many practical applications, due to which to maintain liquids stable within their working area is very important. However, instabilities may lead to the formation of leaking drops outside the bulk liquid, thus it is necessary to transport the detached drops back without overstepping the working area and causing destructive leakage to the system. In this study, we report a novel and facile method to solve this problem by introducing the wedgelike geometry into the parallel gap to form a parallel-nonparallel combinative construction. Transport performances of this structure were investigated. The criterion for self-propelled motion was established, which seemed more difficult to meet than that in the nonparallel gap. Then, we performed a more detailed investigation into the drop dynamics under squeezing and relaxing modes because the drops can surely return in hydrophilic combinative gaps, whereas uncertainties arose in gaps with a weak hydrophobic character. Therefore, through exploration of the transition mechanism of the drop motion state, a crucial factor named turning point was discovered and supposed to be directly related to the final state of the drops. On the basis of the theoretical model of turning point, the criterion to identify whether a liquid drop returns to the parallel part under squeezing and relaxing modes was achieved. These criteria can provide guidance on parameter selection and structural optimization for the combinative gap, so that the destructive leakage in practical productions can be avoided.
在许多实际应用中，由于两平行板之间的液体具有传输、支撑或润滑的功能，因此保持其在工作区域内的稳定非常重要。然而，不稳定性可能导致泄漏液滴在主体液体之外形成，因此有必要将分离的液滴输送回工作区域内，而不会超出工作区域并对系统造成破坏性泄漏。在这项研究中，我们通过在平行间隙中引入楔形几何形状来形成平行-非平行组合结构，从而引入了一种新的简便方法来解决这个问题。我们研究了这种结构的传输性能。建立了自推进运动的准则，与非平行间隙相比，这个准则似乎更难满足。然后，我们对挤压和放松模式下的液滴动力学进行了更详细的研究，因为亲水组合间隙中液滴肯定会返回，而在疏水性较弱的间隙中则存在不确定性。因此，通过探索液滴运动状态的转变机制，发现了一个关键因素，称为转折点，并假设它与液滴的最终状态直接相关。基于转折点的理论模型，实现了识别挤压和放松模式下液滴是否返回平行部分的准则。这些准则可以为组合间隙的参数选择和结构优化提供指导，从而避免实际生产中的破坏性泄漏。
