Super hydrophobic ppt

Review paper on superhydrophilicity

1. A Technical Presentation
on
Superhydrophobic
materials and coatings: a
review
Authored by
JohnTSimpson1,3 , Scott RHunter2 And
TolgaAytug2
1 University Of Tennessee, Knoxville, TW 37996, USA 2 Oak Ridge
National Laboratory, Oak Ridge, TN 37831, USA
Presented by
Reshab Pradhan ( #2110121101 )
PhD Research Scholar
Guided By
Dr. Harpreet Singh Grewal
Associate Professor Room No-C121C
SURFACE SCIENCE AND TRIBOLOGY LAB

2. Motivation & Objective Of the Study
Introduction
Wetting
Wetting Models
Recent Superhydrophobic Breakthroughs
Applications
Summary
Queries
Thank you
CONTEXT

3. Motivation Of the Study
Overthepastfewyears,thescientificcommunity,aswellastheworld’scoatingsindustry
hasseentheintroductionofoxide/polymer-basedsuperhydrophobicsurfacesand
coatingswithexceptionalwaterrepellency.
Sincesuperhydrophobicsurfacesandcoatingscanfundamentallychangehowwater
interactswithsurfaces,andthefactthatearthisawaterworld,itcanlegitimatelybesaid
thatthistechnologyhasthepotentialtoliterallychangetheworld.

4. Wetting
•Thewettingofsurfacesbyliquids,canbeunderstoodbyconsideringadropletofliquidrestingona
surface.Thewettingactioncanbequantifiedusingthevarioustensionsthatactatthepointwherethe
threephases,ofliquid,solidandvapor,meet,asshownbelow.Thetensions,orsurfacetensions,are
representedbythesymbolγ,andthesubscriptsL,SandVstandforliquid,solidandvapor.The
surfacetensionscanbecombinedwiththeequilibriumcontactangle,γLVcosθ
ContactAngle-
•Thecontactangleistheangle,conventionallymeasuredthroughtheliquid,wherealiquid–vapor
interfacemeetsasolidsurface
•Surfacescanbeclassifieddependingontheircontactangleasillustratedinthetable.
•Contactangleisameasurementoftheinteractionenergybetweenthesurfaceandtheliquid.
•Therearesomenaturalmaterialsthathavesuperhydrophobicproperties,suchastheLotusleaf,and
thelegsofthewaterstrider.

5. DynamicContactAngles(AdvancingAndReceding)
Thecontactanglemeasuredduringdropletexpansionisreferredtoasadvancingcontact
angleθ
a.Itisameasureofthedry-wettingbehaviorofaliquidorasurface,i.e.,Ofthefluid
mechanicsonafreshlywettedsurface.
Ontheotherhand,continuouslyremovingliquidfromadropletwilldecreaseitssizeandthus
causedewettingofthesurface.Thecontactanglethatisformedduringshrinkingofthedroplet
isreferredtoasrecedingcontactangleθ
r.therecedingcontactangleisameasureofthe
remaininginteractionforcesbetweentheliquidandthesolid.
Roll-offAngle-Theangleatwhichawaterdroprollsoffatilted
flatsurfaceisknownastheroll-offangle(θR).Generally,super-
Hydrophobicsurfacesexhibitroll-offangleslessthan5degrees.

6. Wetting Models
Effect Of Surface Roughness-
•As roughness goes hand-in-hand with an enlarged surface area, it affects the wettability of a solid, the contact
angle (CA) of a liquid, and the adhesion. Whether the roughness increases or decreases wettability depends
on the degree of wettability of the smooth material. The following observations assume that the scale of
magnitude of the roughness is significantly less than the drop size of the liquid.
•Effect of roughness on wettable surfaces (ca <90°)
Young’sEquation-
•Young’sstaticanddynamiccontactangleequationsarethemostcommonandrelevantparametersdescribing
thewettingpropertyofasurfacewithrespecttoliquidwatercosθY=(σsv–σsl)/σlv.
WenzelandCassie–Baxterregimes-
•Theincreaseofeffectivecontactangleasaresultofsurfaceroughnessandstructuretopographyfallsintotwo
regimes,knownastheWenzelandcassia–Baxterregimes.
•According to Wenzel, the relationship between roughness and contact angle is as follows:
•Θ* = measured (apparent) contact angle; θ = contact angle with the smooth surface; r’ = roughness coefficient

7. Engineered Disordered Superhydrophobic Surfaces
•Thefollowingmicrographsareexamplesofengineered,disordered,nanotexturedsurfaceswhich
areinitiallysuperhydrophilic,butbecomesuperhydrophobicwhentheirsurfacechemistriesare
changedfromhydrophilictohydrophobicbytreatingthesurfaceswithahydrophobicself-
assembled-monolayer(SAM)
i.Superhydrophobicsiliconpostarray
ii.Glassconespikearray
iii.‘MosesEffect’Image.Superhydrophobic14mmdiameterdischaving~1millionconespikes.
iv.Nanotexturedsilicaformedfrometchedphaseseparatingborosilicateglass
v.Nano-texturedfluorinatedpolymerstrands.

8. Figureshowssuperhydrophobicnano-structuredandnano-poroussilicaproducedBy
differentialetchingphaseseparatedborosilicateglass.Thisnano-texturedsuperhydrophobic
structurehasShowncontactanglesashighas178°.
FigureshowsnanostrandsoffluorinatedpolymershavingcontactanglesofRoughly145°.
Notethatthesepolymerstrandsareeasilymatteddown.Whenthathappens,theCAis
quicklyreducedtoBelow130°.
ResearchersfromUCLA[ChoiC-H2006]fabricatedarandomArrayofconespikesproducedby
asymmetricallyetchingasiliconwafer.TheirrandomconespikestructurehadastaticCAof
over170°.

9. Historic limitations of superhydrophobic surfaces
and coatings
Untilrecently,noneofthesesuperhydrophobicmaterialsorsurfaceeffectsmadeitintoany
commercialproducts.Thefollowingisalistofthemajorreasonswhy.
CostIssues-Thecostofsuperhydrophobicmaterialshasbeenrelativelyhighduetotheamountof
processingrequiredtocreatethemicroandnano-structuresnecessaryforsuperhydrophobic
behavior.Forinstance,mostoftheearlysuperhydrophobicmicroandnanostructuredsurfaceswere
producedusingphotolithographywhichcanitselfbeaverycostlyprocess.Butwhenyoucombine
thefactthatnano-scalephotolithographyproducessmallchipdiesthathavetobestitchedtogether
in-ordertocoveranysignificantarea,theoverallcostandperformancecanbeprohibitive.
Nanostructurestability-Ahighquality,highcontactangle,superhydrophobicsurfacerequiresa
hydrophobicsurfacechemistrywithastablemicroandnanotopography.Thisisgenerallynotan
easysetofrequirementstoachieve.Forinstance,polymerswithnano-texturetendtoactlike‘wet
noodles’atthenano-scaleThesepolymerstrand‘wetnoodles’tendtobeeasilymatteddownand
thusquicklylosetheirsuperhydrophobicbehavior.

10. Durability issue-
Even if you use high quality superhydrophobic particles, it’s still not easy to bond such particles to a
substrate without significantly degrading or destroying the superhydrophobic behavior. This tends to
be a classic trade-off condition between durability and superhydrophobic behavior.
Condensation Issues-
Whilesuperhydrophobiccoatingsandsurfacesrepelwater,theydonotrepelwatervapor.Ifthe
coatingisinacondensationcondition(i.e.,Thecoatingtemperatureisbelowthedewpoint)
condensationwilloccur.Whenthisoccurs,theresultingcondensatecanresultinsubstantialsurface
wetting.
Surfactant/oilwettingissues-
Superhydrophobicbehaviorisaresultofamplifying(viathesurfacetopography)theeffectofwater’s
surfacetension.Ifthewater’ssurfacetensionisgreatlyreducedwithasurfactantorwithanoil,
superhydrophobicbehaviorwillbegreatlyreducedoreliminatedandthesurfaceistheneasily
wetted

11. Phases of superhydrophobic technology
•Thefirstphasedealswithbasicresearchofsuperhydrophobicstructuresconductedatvarious
universities,nationallaboratories,andresearchcenters.
•Thesecondsuperhydrophobictechnologyphaseusessomeofthefirstphasematerials(e.g.,
Functionalizednanoparticles)[KamegawaTetal2012]tomakesuperhydrophobiccoatingsinaloosely
boundtop-coat.Notethatthistop-coattypeofsuperhydrophobictechnologyisstrictlyasurface
effectandisexemplifiedbyrustoleum's‘neverwet’product.Ifthecoating’ssurfaceisremovedor
damaged,itssuperhydrophobicbehavioriseliminated.
•Waterdroponfullyfunctionalizedsuperhydrophobicnano-texturedsilicaparticles.
•Watermarblesformedbypartiallyfunctionalizedsuperhydrophobic/superhydrophilicnano-texturedsilicaparticles.

12. Recent superhydrophobic technology breakthroughs
Volumetric SH coatings (paints, epoxies, and silicones)-
Whatismeantby‘volumetricsuperhydrophobic’isacoatingthatissuperhydrophobicthroughoutthe
coating’sentirevolume,fromitsoutersurfaceallthewaytotheunderlyingsubstrate.Suchacoatingwill
dramaticallyrepelwaterevenifthecoating’ssurfacegetsabradedaway.Thisdevelopmentnotonly
makessuperhydrophobiccoatingsmuchmoredurable.Butitalsoexpandsthecapabilitiesof
superhydrophobiccoatingsinentirelynewways(likereducingoreliminatingtheimpingementissues)
Watermarbles-
Sincesilicaisnaturallyhydrophilic,nano-texturedsilicaparticleswillbesuper-hydrophilicandarereadily
wettedbywaterdrops.Iftheparticlesarefullyfunctionalizedwithahydrophobicsilane,theparticleswill
becomesuperhydrophobicandtheywillnotbewettedbywater.Figureshowsawaterdropbeadedupon
suchfullyfunctionalizedsuperhydrophobicparticles.But,iftheparticlesareonlypartiallyfunctionalized,
eachparticlecansimultaneouslyhavebothsuperhydrophobicandsuperhydrophilicareasofbehavior.
Whenwaterdropsinteractwiththeseparticles,‘watermarbles’areformed.Awatermarbleisadropof
waterthatwetsthesuperhydrophilicportionofsuchparticleswhilenotwettingthesuperhydrophobic
portionoftheparticles.

13. Resin Marbles-
Theinteractionofsuperhydrophobicnano-texturedsilica(e.g.,SHDE)withmoltenpowder-coat
resinscanproducewhatresearcheratoakridgenationallaboratorycall‘resinmarbles.Thepowder-
coatprocessusesdrypolymerresinstocoatsurfacesusinganelectrostaticprocess.Oncean
electricallygroundedsurfaceissufficientlycoveredwithchargedresinparticles,thecoatedsurface
isplacedinanovenwheretheresinparticlesbecomemoltenformingauniformlycoatedandcured
powderresinsurface.

14. Oleophobic (Oil Repellant) Surfaces Using SLIPS
Slipperyliquid-infusedporoussurface(s)(SLIPS)surfacesaresurfaceswithnano-porositythathave
beeninfusedwithlowsurfaceenergyliquids.Thesesurfaceshaveshownexceptionalliquid-and
ice-repellency,pressurestabilityandenhancedopticaltransparency.Itisgenerallyagreedthatthe
reasonwhythesesurfacesaresoliquidandicerepellantisthattheycreatesuper-smoothsurfaces.
DurableSuperhydrophobicOpticalThinFilms
Thefourthphaseofsuperhydrophobictechnologywilllikelybethedevelopmentof
commerciallyviable(i.e.,Durable)superhydrophobicopticalthinfilms.
Thethreepropertiesrequiredtomakeadurablesuperhydrophobicopticalthinfilm(namely,
durability,opticalclarity,andsuperhydrophobicbehavior)tendtobemutuallyexclusivemaking
itinherentlydifficulttomakesuchacoating.Forinstance,superhydrophobicbehaviorrequires
aroughtexturedsurfacewhichnormallyscatterslightandthuspreventsopticalclarity.And,in
ordertoMakeadurablethinfilmconsistingofsuperhydrophobicnanoscaleormicro-scaleparticles,
afairamountofbinder(e.g.,Polyurethane)isrequired.

15. Applications Of Durable Superhydrophobic Surfaces And Coatings
Water Repellency-Water repellency is the most obvious application of superhydrophobic
coatings and surfaces. A partial list includes clothing that will be both breathable and water repellant,
umbrellas that stayed completely dry, building materials, paints, epoxies, and silicones.
Self-cleaningOpticalWindowsAndLenses-Opticallyclearsuperhydrophobiccoatingson
glasses,windows,andopticallenseswillmakeseeinginfoulweathermucheasierandcleaning
windowswillbeassimpleassprayingthemwithwater.
ViscousDragReduction-
Superhydrophobicpaintsandepoxiescouldgreatlyreducethecostoftransportinggoodsbyships
andimprovetheefficiencyofwatercraftofallkindsduetothereductionofwaterdragonthe
watercraft’shull.Figure(leftandright)showsatoyboatwithandwithoutathinsuperhydrophobic
coatingonitshull.

16. Anti-icing-Superhydrophobiccoatingsandoil-modifiedsuperhydrophobiccoatingscouldgreatly
reduceoreveneliminatemanyoftheeffectsoficestormsandaircrafticing.
Anti-bio-fouling-SuperhydrophobicCoatings
andoil-modifiedsuperhydrophobiccoatings
Couldreduceoreliminatebio-foulingofshiphulls,
piers,powerplantintakesystemsandothersurfaces.
Unfouledoil-modifiedSH
treated4″×4″epoxyplate
Fouleduncoated4″×4″epoxyplate

17. Anti-corrosion-
Lowpermeabilitypaint,usedasawaterandvaporbarrier,isthestandardwayofprotectingmetal
surfacesfromcorrosion.Suchpaintworkswelluntilthepaintdevelopsmicro-cracks.Atthatpoint,
waterseepsintothemicro-cracks.Fromthenon,thepaint,actingasabarrieractuallyholdsthe
waterinthemicro-cracks,whichfromthatpointonpromotescorrosion.
Desalination-
Volumetricsuperhydrophobiccoatingsaresaltwater-basedcorrosionresistantandcangreatly
reduceorpreventanysaltresiduebuildup.Therefore,itispossiblethattheuseofvolumetric
superhydrophobiccoatingscouldfinallymakelargescaleevaporativedesalinationcommercially
viable.

18. Summary/Observations/Predictions
•Thesesuperhydrophobicsurface-effectmaterialsandcoatingsproducedalotofscientificand
publicinterestinsuperhydrophobicmaterialsbutresultedinaconsiderableamountof
disappointmentwhenthematerialswereshowntobeeithertooexpensiveorlackedadequate
durability.
•Inthiswedescribedasuperhydrophobictechnologyphasebeginningin2015withtheintroduction
ofvolumetricdurablesuperhydrophobicpaints,quicklyfollowedbytheintroductionofdurableand
transparentsuperhydrophobicopticalthinfilms.
•Itisthisbeliefthatthecommercialintroductionofdurablesuperhydrophobiccoatings,paints,and
surfaceswillhaveadramaticworld-wideeffectonnearlyeveryindustryandpossiblyeveryoneon
earth.

20. THANK YOU