Table Of ContentAdvances in Silicon Science
ADVANCES IN SILICON SCIENCE
VOLUME4
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Volume4
SiliconeSurfaceScience
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PetarR.Dvornic
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AdvancesinSiliconScience
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Preface
Godmadethebulk;surfaceswereinventedbythedevil
WolfgangPauli1
It is somewhatsurprising,in our opinion,that this book,to thebest of our knowl-
edge, is the first to be devoted to the surface properties and behavior of silicone
polymers.Thesituationisallthemoreperplexingwhenoneconsidersthatsurface-
relatedapplicationshaveconsistentlyaccountedforthemajorpartofthecommer-
cialsuccessofsiliconessincetheestablishmentofthisindustryintheearly1940s.
The importance of surfaces and interfacial phenomena cannot be overempha-
sized.Whenanytwomaterialsarebroughttogetheritistheirsurfacesthatinitially
matterandtheirinterfacialinteractionsthatneedtobestudiedandunderstoodfirst.
Therefore,inordertocontributetothis,inthisbookweattempttopresentabroad
overviewofthestate-of-the-artofsiliconesurfacesciencebyagroupofwidelyrec-
ognizedexpertsintheirfieldssummarizingboththehistoricaldevelopmentandthe
currentprogressineachselectedarea.Withalmost70yearsofscientificandtech-
nologicalinterestinsiliconeswecanhardlyclaimtoberigorouslycomprehensive,
butwearesurethatthemostexcitingdevelopmentsinthisfieldtodayarecovered
inthisvolume.
Muchofthecontentofthisbookdealswithpolydimethylsiloxane(PDMS)since
it has been the mainstay of the silicone industry from its very beginnings to the
present day. Furthermore, looking into the future, while anticipatingcontinued in-
terest in and development of other polymers derived from organosilicon entities,
thereisnoreasonnottobelievethatthescienceandapplicationsofPDMSandre-
latedorganosiloxanepolymerswillcontinuetogrowandplayasimportantaroleas
theyhaveinthepast.
Asiscommoninthefieldofsilicon-containingpolymers,weusethetermsili-
conetodescribepolymerswhosebackboneissiloxane,i.e.alternatingarrangement
ofsiliconandoxygenatoms,withpendentorganicgroupsattachedtothatbackbone.
Consequently,polyhedraloligomericsilsesquioxanes(POSS),whichcertainlymeet
1Quotedin“Growth,DissolutionandPatternFormationinGeosystems”(1999)byBjornJamtveit
andPaulMeakin,p.291.
v
vi Preface
the“alternatingsiloxanebonds”requirement,arenotusuallyconsidered“silicones”,
becauseoftheirinsufficientmolecularweightsandfundamentallydifferentmacro-
scopicproperties.Nevertheless,weconsidertheseoligomerstobeapropersubject
forinclusioninthisvolumebecauseoftheircriticalimportancetosiliconesurface
scienceasexplainedindetailintwochaptersdealingwithPOSSderivatives.
Whatmightappeartosometobeasomewhatcapriciouschapterorderisbased
on our attemptto marry two seemingly “incompatible”concepts: (i) a progressive
shiftfromfundamentalstomoreappliedtopics,and(ii)adevelopmentfrom“pure”
PDMStootherimportant,surface-activesiliconessuchasfluorosiliconesandmod-
ifiedmaterialssuchassurfactantsandcouplingagents.Thebookopenswithagen-
eralintroductiontosiliconesurfaceswithanemphasisonthesurfacepropertiesof
PDMS.Followingthis,inChap.2AhnandDhinojwaladescribethesumfrequency
generationvibrationalspectroscopyofsiliconesurfacesandinterfaces,arelatively
recentlyintroducedtechniquethat has providedconsiderablenew insightintosur-
facestructureandmostnotablytoburiedinterfacesaswell.Genzerandco-workers
havemadegreatstridesincreatingdifferentfunctionalitiesonsiliconesurfacesand
their contributions are reviewed in Chap. 3. Superhydrophobic surfaces have fea-
tured strongly in the last decade, and McCarthy et al. review their silane/siloxane
studiesofthistopicinChap.4.Chapters5and6dealwithfluorine-containingsili-
coneswhereGanachaudandAmeduriandtheircolleaguesreviewstructure/property
relationshipsinfluorosiliconesandTutejaandMabrycontributeachapteronfluoro-
POSSmaterialswhicharehighlyrelevanttotheearliertopicofsuperhydrophobic-
ity,respectively.Ourstronginterestinfluorosiliconesderivesfromtheirpotentialto
producesignificantlylowersurfaceenergiesthanconventionalPDMSsurfaces.
Langmuir trough investigations of silicones have been of interest since surface
studiesofsiliconesbegan.InChap.7EskerandYuprovideasummaryofthistopic
withanupdateofrecentworksthatoffersanotherfacetofthegrowingimportance
ofPOSScompoundstoorganosiliconsurfacesciencetoday.Atopicofhigh-interest
tocurrentsiloxanesciencewithconsiderablesurface-relatedimplicationsisthein-
teractionofproteinsandsilicon-basedmaterialswhichisthesubjectofChap.8by
Clarsonandco-workers.Thisisfollowedbyareviewofsiliconesurfactantfunda-
mentalsandapplicationsbySnowandPetroffinChap.9,whileMatisons’Chap.10
deals with the adsorption of polymeric siloxanes on glass surfaces and their cou-
pling behavior as well as with more conventional silane coupling agents. Surface
treatments such as plasma and corona have been widely exploited in silicone sur-
face modification.These are summarized in Chap. 11 by Hillborg and Gedde (see
alsoChap.3whichdealswithaspectsofthistopic).
Analyticaltechniquesareself-evidentlycentraltounderstandingofsiliconesur-
face behavior. A review of these studies with emphasis on X-ray photoelectron
spectroscopy (XPS), secondary ion mass spectrometry (SIMS), scanning electron
microscopy(SEM)andscanningprobemicroscopy(SPM)isprovidedbyLeadley,
O’HareandMcMillaninChap.12.Finally,weclosewithanoutlineofsomeimpor-
tantsurfaceapplicationsofsiliconesrelatingtoboththescienceandtechnologyof
siliconesurfaces.Someoftheseapplicationsarealsoincludedinseveraloftheear-
lierchapters,underliningadominantthemeofthisbook,therelationshipbetween
Preface vii
thestructureandsurfacepropertiesofsiliconesandtheirutilizationinvariousevery-
dayaswellasmoresophisticatedapplications.
A variety of authors contributed different perspectives to this work, including
academicandindustrialspecialistsfromEuropeandNorthAmerica.Wesincerely
thankallofthemfortheirimpressivecontributionsandtheirpatienceandpersever-
ance throughout the process of bringing this book to fruition. We are particularly
gratefultoourpublishingeditor,Dr.SoniaOjoandherSpringercolleaguesfortheir
experthelpduringthepreparationofthemanuscriptandtoDonatasAkmanavicˇius
ofVTeXUABintherealizationofthisfinishedwork.
Midland,MI,USA MichaelJ.Owen
PetarR.Dvornic
Contents
1 GeneralIntroductiontoSiliconeSurfaces . . . . . . . . . . . . . . . 1
MichaelJ.OwenandPetarR.Dvornic
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 LiquidSurfaceTension . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 WaterContactAngleStudies . . . . . . . . . . . . . . . . . . . . 7
1.4 SolidSurfaceEnergyDetermination . . . . . . . . . . . . . . . . 10
1.5 ContactMechanicsApproach . . . . . . . . . . . . . . . . . . . . 12
1.6 LangmuirTroughStudies . . . . . . . . . . . . . . . . . . . . . . 15
1.7 OtherSilicones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.8 ConcludingRemarks. . . . . . . . . . . . . . . . . . . . . . . . . 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 SumFrequencyGenerationVibrationalSpectroscopyofSilicone
Surfaces&Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . 23
DongchanAhnandAliDhinojwala
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.1 TheoryofSurface-SensitiveSFG . . . . . . . . . . . . . . 24
2.2.2 ExperimentalSet-upandSampleConsiderations . . . . . . 28
2.2.3 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.2.4 SiliconeCureSystems . . . . . . . . . . . . . . . . . . . . 31
2.3 ApplicationsofSFGtoSiliconeSurfacesandInterfaces . . . . . . 32
2.3.1 SiliconeSurfaceOrientationandRearrangement . . . . . . 32
2.3.2 FrictionandLubrication . . . . . . . . . . . . . . . . . . . 34
2.3.3 Adhesion . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.3.4 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.4 ConclusionsandFutureDirections . . . . . . . . . . . . . . . . . 51
2.4.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.4.2 InstrumentationandTechniques . . . . . . . . . . . . . . . 53
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
ix
x Contents
3 Creating Functional Materials by Chemical and Physical
FunctionalizationofSiliconeElastomerNetworks . . . . . . . . . . . 59
Jan Genzer, Ali E. O˝zçam, Julie A. Crowe-Willoughby, and
KirillEfimenko
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.2 PhysicalModificationofSENSurfaces . . . . . . . . . . . . . . . 62
3.3 ControllingMolecularandMacromolecularPackingUsingSENs . 67
3.4 TurningFlatSENsintoTopographicallyCorrugatedSurfaces . . . 74
3.5 SENasaMaterialPlatformforCreatingResponsive/“Smart”
Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.6 AQuestTowardsUniversalCoatingLayers . . . . . . . . . . . . . 85
3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4 UsingSurface-AttachedOrganosilanestoControlandUnderstand
HydrophobicityandSuperhydrophobicity . . . . . . . . . . . . . . . 95
Joseph W. Krumpfer, Lichao Gao, Alexander Y. Fadeev, and
ThomasJ.McCarthy
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.2 MonofunctionalSilanes:MolecularTopographyandFlexibility
ContributetoContactAngleHysteresis . . . . . . . . . . . . . . . 96
4.3 MethylchlorosilanesReacttoFormSuperhydrophobicSurfaces . . 102
4.3.1 Methyltrichlorosilane and a Perfectly Hydrophobic
Surface[32] . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.3.2 The(CH ) SiCl/SiCl Azeotrope[34] . . . . . . . . . . . 105
3 3 4
4.4 “Unreactive”SiliconesReactwithInorganicSurfaces . . . . . . . 109
4.5 ClosingComments. . . . . . . . . . . . . . . . . . . . . . . . . . 113
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5 ComparisonofSurfaceandBulkPropertiesofPendantandHybrid
Fluorosilicones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Cedric Pasquet, Claire Longuet, Siska Hamdani-Devarennes,
BrunoAmeduri,andFrançoisGanachaud
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5.2 SomeInsightsonFluorosiliconeSynthesis . . . . . . . . . . . . . 117
5.2.1 SynthesisofPendantFluorosilicones . . . . . . . . . . . . 118
5.2.2 SynthesisofHybridFluorosilicones. . . . . . . . . . . . . 121
5.3 SurfaceProperties . . . . . . . . . . . . . . . . . . . . . . . . . . 125
5.3.1 SurfaceTensionofPendantFluorosilicones. . . . . . . . . 125
5.3.2 SurfaceTensionofHybridFluorosilicones . . . . . . . . . 133
5.3.3 ConclusionstoSect.5.3 . . . . . . . . . . . . . . . . . . . 134
5.4 ThermalPropertiesofFluorosilicones . . . . . . . . . . . . . . . . 134
5.4.1 PendantFluorosilicones . . . . . . . . . . . . . . . . . . . 135
5.4.2 HybridFluorosilicones . . . . . . . . . . . . . . . . . . . 136
5.4.3 ConclusionstoSect.5.4 . . . . . . . . . . . . . . . . . . . 146
Contents xi
5.5 SwellingPropertiesofFluorosilicones . . . . . . . . . . . . . . . 146
5.5.1 PendantFluorosilicones . . . . . . . . . . . . . . . . . . . 146
5.5.2 HybridFluorosilicones . . . . . . . . . . . . . . . . . . . 148
5.5.3 ConclusionstoSect.5.5 . . . . . . . . . . . . . . . . . . . 152
5.6 MechanicalPropertiesofFluorosilicones . . . . . . . . . . . . . . 152
5.6.1 PendantFluorosilicones . . . . . . . . . . . . . . . . . . . 152
5.6.2 HybridFluorosilicones . . . . . . . . . . . . . . . . . . . 161
5.6.3 ConclusionstoSect.5.6 . . . . . . . . . . . . . . . . . . . 165
5.7 NewAvenuesinFluorosiliconeElastomerSynthesis . . . . . . . . 165
5.7.1 RandomCopolymers . . . . . . . . . . . . . . . . . . . . 165
5.7.2 BlockCopolymers . . . . . . . . . . . . . . . . . . . . . . 167
5.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
AppendixA DefinitionandMeasurementsofSurfaceTensionforSoft
Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
A.1 DefinitionofSurfaceTension . . . . . . . . . . . . . . . . 171
A.2 MeasurementofLiquidSurfaceTensions . . . . . . . . . . 172
A.3 MeasurementofSolidSurfaceTensions . . . . . . . . . . 173
Appendix B Swelling Measurements, Solubility Parameters and
PDMSCase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
6 TheDesignofNon-wettingSurfaceswithFluoroPOSS . . . . . . . . 179
AnishTutejaandJosephM.Mabry
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
6.1.1 Non-wettingSurfaces . . . . . . . . . . . . . . . . . . . . 179
6.1.2 FluoroPOSS . . . . . . . . . . . . . . . . . . . . . . . . . 180
6.1.3 DesignParameters . . . . . . . . . . . . . . . . . . . . . . 182
6.2 PreparationofMaterials . . . . . . . . . . . . . . . . . . . . . . . 184
6.2.1 FluorodecylPOSSSynthesis . . . . . . . . . . . . . . . . 184
6.2.2 FluoroPOSSCompositePreparation . . . . . . . . . . . . 185
6.3 CharacterizationTechniques . . . . . . . . . . . . . . . . . . . . . 185
6.3.1 ContactAngleAnalysis . . . . . . . . . . . . . . . . . . . 185
6.3.2 Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . 186
6.4 FluoroPOSSMaterialProperties . . . . . . . . . . . . . . . . . . 186
6.4.1 FluoroPOSSCompounds . . . . . . . . . . . . . . . . . . 186
6.4.2 FluoroPOSSComposites . . . . . . . . . . . . . . . . . . 186
6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
7 LangmuirMonolayersofSiloxanesandSilsesquioxanes . . . . . . . 195
AlanR.EskerandHyukYu
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
7.2 SiliconeLangmuirFilms . . . . . . . . . . . . . . . . . . . . . . 195
7.2.1 SurfacePressure-AreaperRepeatUnit(Π-A)Isotherms
ofPDMSLangmuirFilms . . . . . . . . . . . . . . . . . . 196
7.2.2 ViscoelasticPropertiesofPDMSLangmuirFilms . . . . . 199
