Department of Mechanical Engineering and Mechanics, Drexel University , 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States.
ACS Appl Mater Interfaces. 2016 Mar 2;8(8):5729-36. doi: 10.1021/acsami.6b00852. Epub 2016 Feb 19.
Superhydrophobic surfaces enhance condensation by inhibiting the formation of an insulating liquid layer. While this produces efficient heat transfer at low supersaturations, superhydrophobicity has been shown to break down at increased supersaturations. As heat transfer increases, the random distribution and high density of nucleation sites produces pinned droplets, which lead to uncontrollable flooding. In this work, engineered variations in wettability are used to promote the self-organization of microscale droplets, which is shown to effectively delay flooding. Virus-templated superhydrophobic surfaces are patterned with an array of superhydrophilic islands designed to minimize surface adhesion while promoting spatial order. By use of optical and electron microscopy, the surfaces are optimized and characterized during condensation. Mixed wettability imparts spatial order not only through preferential nucleation but more importantly through the self-organization of coalescing droplets at high supersaturations. The self-organization of microscale droplets (diameters of <25 μm) is shown to effectively delay flooding and govern the global wetting behavior of larger droplets (diameters of >1 mm) on the surface. As heat transfer increases, the surfaces transition from jumping-mode to shedding-mode removal with no flooding. This demonstrates the ability to engineer surfaces to resist flooding and can act as the basis for developing robust superhydrophobic surfaces for condensation applications.
超疏水表面通过抑制形成绝缘液层来增强冷凝。虽然在低过饱和度下产生了高效的传热，但超疏水性已被证明在过饱和度增加时会失效。随着传热的增加，成核点的随机分布和高密度会产生固定的液滴，从而导致不可控的泛滥。在这项工作中，通过工程手段改变润湿性，以促进微尺度液滴的自组织，从而有效地延迟泛滥。采用病毒模板的超疏水表面被图案化为具有一系列超亲水岛的阵列，旨在最小化表面附着力，同时促进空间有序性。通过使用光学和电子显微镜，在冷凝过程中对表面进行优化和表征。混合润湿性不仅通过优先成核赋予空间有序性，而且更重要的是通过在高过饱和度下的合并液滴的自组织赋予空间有序性。微尺度液滴（直径 <25μm）的自组织有效地延迟了泛滥，并控制了表面上较大液滴（直径 >1mm）的整体润湿行为。随着传热的增加，表面从跳跃模式转变为无泛滥的液滴脱落模式。这表明可以设计表面来抵抗泛滥，并可以作为开发用于冷凝应用的稳健超疏水表面的基础。
