Despite the enormous interest in superhydrophobicity for self-cleaning, a clear picture of contaminant removal is missing, in particular, on a single-particle level. Here, we monitor the removal of individual contaminant particles on the micrometer scale by confocal microscopy. We correlate this space- and time-resolved information with measurements of the friction force. The balance of capillary and adhesion force between the drop and the contamination on the substrate determines the friction force of drops during self-cleaning. These friction forces are in the range of micro-Newtons. We show that hydrophilic and hydrophobic particles hardly influence superhydrophobicity provided that the particle size exceeds the pore size or the thickness of the contamination falls below the height of the protrusions. These detailed insights into self-cleaning allow the rational design of superhydrophobic surfaces that resist contamination as demonstrated by outdoor environmental (>200 days) and industrial standardized contamination experiments.

中文翻译：

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何时以及如何自动清洁超疏水表面。

尽管人们对超疏水性具有很强的自清洁性，但尤其是在单个颗粒的水平上，仍然缺少清除污染物的清晰画面。在这里，我们通过共聚焦显微镜监测微米尺度上单个污染物颗粒的去除。我们将此空间和时间解析信息与摩擦力的测量值相关联。液滴与基材上的污染物之间的毛细管力和粘附力的平衡决定了自清洁过程中液滴的摩擦力。这些摩擦力在微牛顿的范围内。我们显示，只要粒径超过孔径或污染物的厚度低于突起的高度，亲水性和疏水性颗粒几乎不会影响超疏水性。