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无微结构纳米结构化超疏水表面上增强的聚并诱导液滴跳跃。

Enhanced Coalescence-Induced Droplet-Jumping on Nanostructured Superhydrophobic Surfaces in the Absence of Microstructures.

机构信息

Institute of Refrigeration and Cryogenics, MOE Key Laboratory for Power Machinery and Engineering, Shanghai Jiao Tong University , Shanghai 200240, China.

Department of Mechanical Engineering, Thermofluid Physics Laboratory, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.

出版信息

ACS Appl Mater Interfaces. 2017 Oct 11;9(40):35391-35403. doi: 10.1021/acsami.7b09681. Epub 2017 Sep 28.

Abstract

Superhydrophobic surfaces are receiving increasing attention due to the enhanced condensation heat transfer, self-cleaning, and anti-icing properties by easing droplet self-removal. Despite the extensive research carried out on this topic, the presence or absence of microstructures on droplet adhesion during condensation has not been fully addressed yet. In this work we, therefore, study the condensation behavior on engineered superhydrophobic copper oxide surfaces with different structural finishes. More specifically, we investigate the coalescence-induced droplet-jumping performance on superhydrophobic surfaces with structures varying from the micro- to the nanoscale. The different structural roughness is possible due to the specific etching parameters adopted during the facile low-cost dual-scale fabrication process. A custom-built optical microscopy setup inside a temperature and relative humidity controlled environmental chamber was used for the experimental observations. By varying the structural roughness, from the micro- to the nanoscale, important differences on the number of droplets involved in the jumps, on the frequency of the jumps, and on the size distribution of the jumping droplets were found. In the absence of microstructures, we report an enhancement of the droplet-jumping performance of small droplets with sizes in the same order of magnitude as the microstructures. Microstructures induce further droplet adhesion, act as a structural barrier for the coalescence between droplets growing on the same microstructure, and cause the droplet angular deviation from the main surface normal. As a consequence, upon coalescence, there is a decrease in the net momentum in the out-of-plane direction, and the jump does not ensue. We demonstrate that the absence of microstructures has therefore a positive impact on the coalescence-induced droplet-jumping of micrometer droplets for antifogging, anti-icing, and condensation heat transfer applications.

摘要

超疏水表面由于能够增强冷凝换热、自清洁和抗结冰性能,从而使液滴易于自动脱离,因此受到越来越多的关注。尽管针对这一主题已经开展了广泛的研究,但在冷凝过程中,微结构对液滴附着的影响仍未得到充分解决。在本工作中,我们因此研究了具有不同结构表面的工程化氧化铜超疏水表面上的冷凝行为。更具体地,我们研究了在具有从微米到纳米结构的超疏水表面上,由于合并诱导的液滴跳跃性能。由于在简单、低成本的双尺度制造过程中采用了特定的蚀刻参数,因此可以获得不同的结构粗糙度。在温度和相对湿度可控的环境室内,使用定制的光学显微镜装置进行了实验观察。通过改变结构粗糙度,从微米到纳米,我们发现参与跳跃的液滴数量、跳跃频率以及跳跃液滴的尺寸分布都有重要差异。在没有微结构的情况下,我们报告了在与微结构同数量级的小液滴的跳跃性能增强。微结构会进一步引起液滴附着,作为同一微结构上生长的液滴合并的结构障碍,并导致液滴相对于主表面法线的角度偏差。因此,在合并时,垂直于平面的净动量会减小,跳跃不会发生。我们证明,对于防雾、防冰和冷凝换热应用,不存在微结构对微米液滴的合并诱导液滴跳跃具有积极影响。

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