Download Hydrophobic Surfaces Under the SEM_Information Sheet-jw

Unlikeabsorbentcloth,whereadropoffluidspreadsacrossthesurfaceandsoaksin,somesurfacesrepel
water.Thesearecalledhydrophobic,literallymeaningwater-hating.Fluid,likewater,pilesupintoaball
andcanrollaroundoverthesurfacewithouteverwettingit.Seeifyoucanfindwaterdropssittingonthe
leavesshownbelow,insteadofspreadingacrosstheirsurfaces.
Lotusleaves
Thiseffectisseenonthesurfaceoflotusleaves(imageabove).Theseplantsarelikewater-liliesandlivein
water-waysandponds.Notonlydoesthespecialleafsurfacekeeptheleafdry,probablysoitcanstandup
abovethepond,butalso,anydropsofwaterthatrollaroundpickupdirtandcarryitoff,cleaningthe
surface.Manykindsofplantshaveleavesthatarehydrophobic.
Boththechemistryandtheshapeofstructuresareinvolvedincreatingwater-repellentsurface.
Asheetofpapercoveredincandleorbeeswaxwillrepelwater.Thisisachemicalmethodofcreating
hydrophobicity.
Asurfacecanalsobechangedsothatinsteadofbeing
smoothitisrough,coveredforexamplewithlotsoflittle
pillarsorpimples.Findthepillarsinthediagram.Thisisa
physicalmethodofcreatinghydrophobicity.Theroughness
providesmuchlesscontactwiththematerial.Thepillarshold
thewaterawayfromthesurfacesothatitstaysinaround
drop.
Lotusleavescombinethesetwomethodsofchemicalandphysicalmodification.Theyhavelittletubesof
waxarrangedintoclustersorpimple-likeshapes.UsingtheSEMSimulatorsamples,comparetheleaf
surfacesoftwodifferentlotusplantsandseeifalllotusleavesusethesamestructures.
Termitewingsurfaces
Someinsectwingsalsorepelwater.Termiteshavewingedadultsandthesecreaturesliveingroupscalled
coloniesinthegroundorindeadwood.Whentheywanttomakeanewnestthewingedadultsflyawayto
searchforasuitableplace.
Tokeepfrombecomingthefoodofbirdsorotheranimals,somekindsoftermitesflyonrainydaysoreven
inrain-storms.Thedangerforthemthenisthattheirbigfloppywingswillgetwetandcausethemto
crash.Ortheymaysticktowetsurfacesstoppingthemgettingveryfar.Sotheseinsectshavesolvedtheir
problemwithspecialstructuresonthewingsthatmakethemwater-repellant.Hairsholdlargedropsaway
fromthesurfaceandtinystar-shapedpyramidsholdupsmallerdropsthatgetpastthehairs.Lookforthe
specialstructuresbyusingtheSEMSimulatorandthetermitesample.
Addingstructurestosurfaceslikeinsectwingswillinevitablyincreasetheirweight.Theheavierawing,the
moreenergyittakestouseit.Youmightliketomakeamodelofawingsurfacewithvariousstructures.
Measurethestructuresfromdownloadedandprintedimagestogetthedimensionscorrect.Forhowto
measureobjectsshownintheimages,seeMeasuringMicroscopicThingsInformationSheet.
Tryusingdifferentshapes.Modellingclaycanbeusedtomakethestar-likeshapes,aswellasclosed-in
solidpyramidshapes,forexample.Keeptheheightandwidthatthebasethesame.Youcanthenweigh
themtoworkoutifthestarssavemoreweightthansimilarbutsolidshapes.
Termitewingshedding
Termiteshavelotsofcleversolutions.Oncetheylandinasuitableplaceforanewnesttheycangetridof
theirwings,whicharenotusefulwhendiggingorburrowing.Eachwinghasalineofweaknessatthetop.
SeeifyoucanfindthatseparationlineforthetermitesampleavailableintheSEMSimulator.
Geckoskin
Somereptileshavewater-repellentskins.Geckosarebetterknownforbeingabletosticktosurfacesby
usingthefinehairsontheirfeet.Adhesionoccursbecausetinyhairsincreasesurfacearea.Hairsalsooccur
onthebody,butinadifferentformthatrepelswater.UsingtheSEMSimulator,findthehairs.Howbigare
they?Measurethesizeofthehairs.Dotheydifferbetweenthemoundsandflatareasoftheskin?
Internetresources
Humanshavebeenbusymimickingthewater-repellentsurfacesusedbynature:
https://www.youtube.com/watch?v=FLegmQ8_dHg
https://www.youtube.com/watch?v=IPM8OR6W6WE
Thelotusleafeffect:
http://www.nanowerk.com/spotlight/spotid=19644.php
Termitewingstructures:
http://www.abc.net.au/science/articles/2010/02/08/2809284.htm
Geckoskin:
https://www.youtube.com/watch?v=-6NanmAlDqE
http://www.wimp.com/waterproofgecko/
Forevenmorechallengingsciencethereareanumberofopen(free)resourcesonmimickingnature:
http://www.intechopen.com/books/on-biomimetics
http://www.intechopen.com/books/biomimetics-learning-from-nature