Biologicaltinystructureshavebeenobservedonmanykindsofsurfacessuchaslotusleaves,whichhaveaneffectonthecolorationofMorphobutterfliesandenhancethehydrophobicityofnaturalsurfaces.Weinvestigatedthemicro-scaleandnano-scalestructuresonthewingsurfacesofinsectsandfoundthatthehierarchicalmultipleroughnessstructureshelpinenhancingthehydrophobicity.Afterexamining10ordersand24speciesofflyingPterygotaninsects,wefoundthatmicro-scaleandnano-scalestructurestypicallyexistonboththeupperandlowerwingsurfacesofflyinginsects.Thetinystructuressuchasdenticleorsetaeontheinsectwingsenhancethehydrophobicity,therebyenablingthewingstobecleanedmoreeasily.AndthehydrophobicinsectwingsundergoatransitionfromCassietoWenzelstatesatpitch/sizeratioofabout20.Inordertoexaminethewettingcharacteristicsonaroughsurface,abiomimeticsurfacewithmicro-scalepillarsisfabricatedonasiliconwafer,whichexhibitsthesamebehaviorastheinsectwing,withtheCassie-Wenzeltransitionoccurringconsistentlyaroundapitch/widthvalueof20.
