多级特征尺寸亲水-疏水组合壁面滴状冷凝强化

Hydrophobic-hydrophilic combined surface (HCS) is one kind of the promising functional interfacial materials for regulating surface DWC, due to its ability of controlling the dynamic characteristics of multiscale condensing droplets. However, the combined design has not yet reached the desired condensation performance, greatly hindering the development of high-efficiency condensation surfaces. In the project, the droplet behaviors and DWC efficiency are to be studied on the hierarchical-feature-size HCS with sub-millimeter lattices, micro-bulges, and nano-units. Through designing and fabricating HCS with different sizes and visualization condensation experiments, the dynamics of the condensing droplets are to be discussed to obtain the DWC-enhanced relationship between the sizes of the condensed droplets and hierarchical feature sizes of the condensing surfaces. The main aim is to quantitatively describe the formation conditions of high-efficiency condensation on HCS, providing the theoretical basis and designing parameters for HCS materials. The research of the project will give a direction for the optimization of DWC on complex wetting surface, and promote the experimental and theoretical processes of gas-liquid phase transition in micro-space.

亲水-疏水组合壁面可有效实现对多尺度冷凝液滴动态行为调控，成为极具潜力的强化、控制滴状冷凝的功能结构壁面之一。然而，目前亲水-疏水组合的设计尚未达到理想的冷凝特性，极大阻碍了高效冷凝壁面的发展。本课题拟对具备“亚毫米格子-微米凸起-纳米单元”三级结构的亲水-疏水组合壁面上的冷凝液滴行为以及滴状冷凝效率进行研究。通过设计、制备不同特征尺寸的亲水-疏水组合壁面及可视化冷凝实验，探讨冷凝壁面上液滴动态行为规律，获得强化冷凝的冷凝液滴行为尺寸与壁面多级特征尺寸的逐级匹配关系，重点突破亲水-疏水组合壁面高效滴状冷凝形成条件的定量化规律，为亲水-疏水组合壁面材料提供理论依据与设计参数。项目的开展将为复杂润湿界面滴状冷凝的优化提供方向，推动微细空间气液相变的实验和理论进程。

本课题基于“液滴尺寸-壁面结构”逐级匹配原则，开发了一种简单的表面多级结构制备方法，制备了具有润湿差异的“纳米棒-微米球-亚毫米区域“的三级特征尺寸结构壁面。在此壁面上对冷凝液的动态行为进行了研究，重点分析了壁面“纳米棒”及“微米球”结构对冷凝前期液滴润湿行为及液滴群分布的影响，探究了“亚毫米”亲水-疏水跨域液滴传输行为规律，获得了冷凝液滴与壁面特征尺寸的逐级匹配关系。课题执行期间搭建了冷凝实验平台，实现了多因素可控的冷凝性能测试，综合考虑壁面过冷度、亲疏水区域润湿差、壁面微结构和润湿区域尺寸的影响，探究了”壁面冷凝效率-液滴动力学参数-亲疏水微纳结构“的关联机制。最后以提高壁面冷凝效率为目标，对亲疏水组合壁面的多级结构尺寸和润湿特性进行了优化。在当前实验环境中最优的壁面结构如下：“纳米棒”直径约为100纳米，“微米球”直径约为1.6微米，亲水/疏水的宽度比约为2:1，亲水区域静态接触角接近0度，疏水区域静态接触角为160度，实验测得该参数下的亲水-疏水组合壁面的冷凝效率约为超疏水壁面的1.6倍。此外，将多级特征尺寸的研究思路推广到固液相变材料的设计过程中，实现了“壳-核“复合相变材料的制备和其相变特性如相变点和相变潜热的控制。