HYDROPHOBIC-HYDROPHILIC.ppt

HYDROPHOBIC-HYDROPHILIC

1. MANOJ KUMAR
III Semester
ME
Seminar on
HYDROPHOBIC AND HYDROPHILIC

2. •Someofthecommonnatural
Hydrophobicmaterialsare
waxes,oilandfats.
HydrophobicitycomesalsofromthegreekwordHydro(water)
andPhobicity(fear)itreferstothephysicalpropertyofa
materialthatrepelsamassofwater.
WHAT IS MEANT HYDROPHOBICITY ?
Theevaluationofhydrophobicity
ismadethroughwatercontact
anglemeasurements.
Awaterdropletwouldbe
sphericalsothewatercontact
anglewillbesignificantlyhigh.

3. •Atthemolecularlevel,thehydrophobiceffectisimportantin
drivingproteinfoldingformationoflipidbilayersandmicelles,
insertionofmembraneproteinsintothenonpolarlipid
environmentandprotein-smallmoleculeinteractions.Substances
forwhichthiseffectisobservedareknownashydrophobes.
HYDROPHOBIC EFFECT
Thehydrophobiceffectrepresentsthe
tendencyofwatertoexcludenon-polar
molecules.Theeffectoriginatesfrom
thedisruptionofhighlydynamic
hydrogenbondsbetweenmoleculesof
liquidwater.
Continued….

4. SUPER HYDROPHOBIC COATING
Superhydrophobictechnology
makeswaterbounce,itstopsit,
rollsitoffthesurface.
Theprocessofcoatingthesurfaceofamaterialwithhydrophobic
propertymaterialinordertoavoidstickingofliquidsonthatsurface.
Thisisabsolutelyuniquewayofcoatingunlikeconventionalwhich
shrinkcontinuouslyduringdryingtoproducelowporosityfilms.

5. Young's equation is used to describe the interactions between
the forces of cohesion and adhesion and measure what is
referred to as surface energy.
www.ramehart.com/contactangle.htm

6. •A drop with a contact angle over 90°is hydrophobic.
•Thisconditionisexemplifiedbypoorwetting,poor
adhesivenessandthesolidsurfacefreeenergyislow.
Continued..

7. Hydrophobic interactions
•Hydrophobic interactions describe the relations between water
and hydrophobes (low water-soluble molecules).
•Hydrophobes are nonpolar molecules and usually have a long
chain of carbons that do not interact with water molecules.
•The mixing of fat and water is a good example of this
particular interaction.
•The common misconception is that water and fat doesn’t mix
because the Van der Waals
•forces that are acting upon both water and fat molecules are
too weak.

8. Causes of Hydrophobic Interactions
•AmericanchemistWalterKauzmanndiscoveredthatnonpolar
substanceslikefatmoleculestendtoclumpuptogetherrather
thatdistributingitselfinawatermedium,becausethisallowthe
fatmoleculestohaveminimalcontactwithwater.
Hydrophobic interactions -
ChemWiki

9. Formation of Hydrophobic Interactions
•Themixinghydrophobesandwatermoleculesisnot
spontaneous;however,hydrophobicinteractionsbetween
hydrophobesarespontaneous.
•Whenhydropobescometogetherandinteractwitheachother,
enthalpyincreases(ispositive)becausesomeofhydrogenbonds
thatformtheclathratecagewillbebroken.
•Tearingdownaportionoftheclathratecagewillcausethe
entropytoincrease(ispositive),sinceformingitdecreasesthe
entropy.

10. According to the formula: ΔG= ΔH-TΔS
ΔH=Small positive value
ΔS=Large positive value
Result :ΔG= Negative
A negative ΔG indicates that hydrophobic interactions are spontaneous

11. What does the strength of Hydrophobic Interactions depend on?
•Temperature
•Number of carbons on the hydrophobes
•The shape of the hydrophobes
In order of Effectiveness:

12. APPLICATIONS
•Aprimarypurposeofhydrophobiccoatingssuchas
polytetrafluoroethylene(PTFE)orpolyxylyleneistoactasa
barrieragainstwatercommonlyseeninautomobiles
•Usedinfabricationonmetallicnanorodtopreventicing.
•Itsiswidelyusedinaerospaceindustryforprovidinganti-icing
coatingonthesurfaceoftheaeroplane.
•Hydrophobicselfcleaningglassesareinstalledintrafficsensor
controlunit.
•Weinducehydrophobicrecoveryafterplasmatreatment,a
physicalcontacttreatment(PCT).

14. Hydrophilicity,alsocomesfromtheGreekwordHydro(water)
andPhilicity(friendship)itreferstoaphysicalpropertyofa
materialthatcantransientlybondwithwater(H
2O)through
hydrogenbonding.Furthermoreitallowstheliquidtoenterthe
poresofamaterialandtotallywetit.
WHAT IS MEANT HYDROPHILICITY ?
•Almost all natural materials are
hydrophilic in nature.
Theevaluationofhydrophilicityis
madethroughwatercontactangle
measurements.Awaterdroplet
wouldoccupyaslongsurfaceofthe
hydrophilicmaterialaspossible.So
thewatercontactanglewillbe
significantlylow.

15. •Thisisthermodynamicallyfavorable,andmakesthese
moleculessolublenotonlyinwaterbutalsoinotherpolar
solvents.Therearehydrophilicandhydrophobicpartsofthe
cellmembrane.
•Ahydrophilicmoleculeorportionofamoleculeisonethatis
typicallycharge-polarizedandcapableofhydrogenbonding,
enablingittodissolvemorereadilyinwaterthaninoilor
otherhydrophobicsolvents.
Hydrophiliccoatingswetthesurface
veryeasily,andmaintainthewetnessfor
longertime.Thus,usinghydrophilic
coatingseliminatestheneedfor
additionallubricants.
HYDROPHILIC COATING
Continued…

16. Here ,also we use same figure of young’s equation to explain
hydrophilicity
A drop with a small contact angle
is hydrophilic.
This condition reflects better
wetting, better adhesiveness, and
higher surface energy.

17. Hydrophilic Interactions
Interactionsbetweenwaterandothermoleculessuchthatthe
othermoleculesareattractedtowaterarecalledhydrophilic
interactions.
Molecules that have charged parts to them are attracted to the
charges within the water molecule.
This is an important reason why water is such a good solvent

18. Continued….
Glucosemoleculeshavepolarhydroxyl(OH)groupsinthemand
theseattractthewatertothem.Whensugarisinacrystalthe
moleculesareattractedtothewaterandgointosolution.
Onceinsolutionthemoleculesstayinsolutionatleastinpart
becausetheybecomesurroundedbywatermolecules.Thislayerof
watermoleculessurroundinganothermoleculeiscalledahydration
shell.

19. What does the strength of Hydrophilic Interactions depend on?
•Inhibitoryeffectmainlydependedontheirconcentrationandtoa
lesserextentontheionchargeandhydratedionradii.
•Stepwiseregressionanalysisprovedthatthestrengthof
interactiondependsonthepolarityparametersofaminoacids
andisindependentoftheirchemicalstructure.

20. APPLICATIONS
•Spray Painting
•Film coating
•Bio-Medical

21. Wenzeland CassieStates of Wetting
Here are two natural parameter:
Afirstnaturalandsimpleeffectarisingfromthepresenceof
microstructuresisanincreaseofthesurfaceareaofthematerial.
r=1+2πbh/p
2
we can define two levels; namely, the top of the posts and the ground
on which they sit.
Asecondnaturalparameteristheratioϕ
Sbetweenthetopand
bottomsurfaceareas,whichisalsothepostdensity.
ϕ
S= πb
2
/p
2

22. Whendepositingawaterdroponasuchsolid.Itcanadoptat
leasttwotypeofconfiguration-
QuéréD,ReyssatMPhil.
Trans.R.Soc.
A2008;366:1539-1556
conforming to the solid surface (Wenzel situation)
Sitting on the top of the posts((Cassie or fakir state)

23. www.me.umn.edu/~lixxx099/EFRI_CAES/Research/texturing.htm

24. TheSecondandsimplestpictureistheso-calledWenzelstate
(figurethedropjustfollowsthestructuresonthematerial
(Wenzel1936).
Thiswillaffectboththewetting(thevalueoftheequilibrium
angle,thatistheonewhichminimizesthesurfaceenergyofthe
drop)andtheadhesion(characterizedherebythevalueofthe
contactanglehysteresis).
cosθ
*
=r cosθ
Wenzel state

25. Cassie state-Fakir state
Thirdfig.impliesthecreationofaliquid–vapourinterfacebelowthe
drop,onafractionofsurfaceoftheorderof1−ϕS,consideringthese
interfacesasflat(thedropislargecomparedwiththepillars,
implyinganegligiblecurvatureoftheliquid–vapourinterfaceatthe
scaleofpillars).
Thecosineoftheapparentcontactangleisthenanaveragebetween
thecosineoftheYoungangleandthecosineof180°,theangleofa
waterdroponair,wheretheweightsfortheaverageare,respectively,
ϕSand1−ϕS.
cosθ
*
= -1 + Φ
s(1+cosθ)
(Cassie & Baxter 1944)

27. THANKS