Fog-harvesting inspired by the Stenocara beetle-An analysis of drop collection and removal from biomimetic samples with wetting contrast

This work examines the fog-harvesting ability of patterned and non-patterned samples in spray chamber experiments. The samples were prepared from different materials and the patterns under investigation were channels, hydrophobic patches and hydrophilic patches of contrasting wettability to mimic and optimize the alleged natural fog-harvesting ability of the Stenocara beetle. Fog-harvesting results based on the amount of collected water showed no significant differences among all samples, as the influence of wind was found to be the more dominant factor compared to the samples' wetting characteristics. Video analysis of the experiments, however, revealed differences in the water collection and water removal mechanisms and were concluded to be more helpful than water collection results in the assessment of the various competing mechanisms in fog-harvesting experiments. The analysis with regard to surface wettability is based on drop rolling on the surface and roll-off into air, respectively. All patterned and most non-patterned samples exhibited drop motion by coalescence rather than rolling. Larger coalesced drops of non-spherical shape with irregular triple line shapes span the surface pattern on all our surfaces, which suggests that the underlying pattern of the surface has no dominant effect on the behavior of the droplets on these surfaces. (C) 2013 Elsevier B. V. All rights reserved.