Not All Sizes of Dust can be Removed by Jumping Condensates on Superhydrophobic Surfaces

It is well known that superhydrophobic surfaces (SHSs) possess self-cleaning ability, either by impacting or rolling water droplets or by self-propelled jumping condensate. However, contaminants that are present in the air are various. Is it possible that these contaminants can all be removed from SHSs by jumping condensate? In this study, hydrophilic SiO₂ micro- or nanoparticles with diameters larger than, comparable to, and smaller than the width of the nanogaps of the SHS were first filled in the nanogaps or suspended on the nanostructures with the help of ethanol, and the resulting SHS was exposed to condensing water vapor. Direct observation through microscopy showed that jumping condensation was still obvious on the SHS that were capped or filled with micro- or nanoparticles. Scanning electron microscopy (SEM) imaging demonstrated that following jumping condensation, particles that possessed diameters significantly smaller or larger than the width of the nanogaps were both removed from the SHS. However, most particles possessing diameters comparable to the width of the nanogaps remained on the SHS. This confirms for the first time that not all contaminants or dust can be removed from an SHS by self-propelled jumping condensate. Furthermore, the study also simply demonstrates that vapor condensation occurs within the nanogaps of the SHS. This study is helpful in further understanding the mechanism of the self-cleaning caused by jumping condensate and exploring the initial formation of condensate droplets on the SHS.