Liquid surfaces and interfaces : synchrotron X-ray methods

336 Pages·2012·8.006 MB·English

by  Professor Peter S. Pershan, Mark Schlossman

LiquidSurfacesandInterfaces
SynchrotronX-rayMethods
TheavailabilityofsynchrotronX-raysourceshasradicallytransformedmuchofX-ray
physics.Subsequentdevelopmentsdescribedinthisbookhaveledtosubstantialprogress
inourunderstandingofmolecularorderingatliquidinterfaces,withrelevancetomany
areasofscienceandtechnology.Thispracticalguideonthesubjectwillenablegraduate
students and researchers to understand and carry out experimental investigations into
thebasicphysicalandchemicalpropertiesofliquidsurfacesandinterfaces.
The book examines the surfaces of bulk liquids, thin wetting films, and buried
liquid/liquidinterfaces.Itdiscussesexperimentsonsimpleandcomplexfluids,includ-
ingpurewaterandorganicliquids,liquidcrystals,liquidmetals,electrifiedliquid/liquid
interfaces, and interfacial monolayers of amphiphiles, nanoparticles, polymers, and
biomolecules.Adetaileddescriptionoftheapparatusandtechniquesrequiredforthese
experimentsisprovided,andtheoreticalapproachestodataanalysisaredescribed,includ-
ingapproximatemethodssuchasthemasterformula,theBornapproximation,Parratt’s
algorithm, and the distorted-wave approximation. It is ideal for people working in
physics,chemistry,biology,andmaterialsscience.
PeterS.PershanisFrankB.Baird,Jr.ProfessorofScienceinthePhysicsDepartmentand
theSchoolofEngineeringandAppliedScienceatHarvardUniversity.Intheearly1980s
hehelpedproducethefirstsynchrotronX-rayreflectometerforstudyofthehorizontal
liquid surface. He has since led the liquid surface field in exploration of such diverse
liquidsurfacesassuperfluidhelium,water,andliquidmetals.
Mark L. Schlossman is a Professor in the Department of Physics at the University of
Illinois at Chicago. He built an X-ray reflectometer at the NSLS that subsequently
servedasaprototypewhenhehelpeddesigntheChemMatCARS instrumentfeatured
inthisbook.Hisuseofbothreflectometersledtopioneeringstudiesofthestructureof
liquid/liquidinterfaces.

Liquid Surfaces and Interfaces
Synchrotron X-ray Methods
PETER S. PERSHAN
HarvardUniversity,Massachusetts
MARK L. SCHLOSSMAN
UniversityofIllinois,Chicago
CAMBRIDGEUNIVERSITYPRESS
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Informationonthistitle:www.cambridge.org/9780521814010
(cid:2)C PeterS.PershanandMarkL.Schlossman2012
Thispublicationisincopyright.Subjecttostatutoryexception
andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
Firstpublished2012
PrintedintheUnitedKingdomattheUniversityPress,Cambridge
AcatalogrecordforthispublicationisavailablefromtheBritishLibrary
LibraryofCongressCataloginginPublicationdata
Pershan,PeterS.,1934–author.
Liquidsurfacesandinterfaces:synchrotronX-raymethods/PeterS.Pershan,HarvardUniversity,
Massachusetts,MarkSchlossman,UniversityofIllinois,Chicago.
pages cm
Includesbibliographicalreferencesandindex.
ISBN978-0-521-81401-0(hardback)
1.Liquid-liquidinterfaces. 2.Synchrotronradiation. 3.X-rayspectroscopy.
I.Schlossman,Mark,author. II.Title.
QD509.L54P47 2012
530.4(cid:3)27–dc23 2012021839
ISBN978-0-521-81401-0Hardback
CambridgeUniversityPresshasnoresponsibilityforthepersistenceor
accuracyofURLsforexternalorthird-partyinternetwebsitesreferredto
inthispublication,anddoesnotguaranteethatanycontentonsuch
websitesis,orwillremain,accurateorappropriate.
ToPatPershanwhosepatientandlovingsupportmademymid-careerpursuit
ofsynchrotronexperimentspossible.Shegraciouslyenduredoverthirtyyears
oflonelydaysandnightsofsynchrotrontravelinorderthatthisbook
couldbewritten.
ToMark’swifeBinhuaLinwhoseadventuresinX-raystudiesofliquidsurfaces
havemadehisownstudiesthatmuchmorepleasant,andtotheirdaughter
Elizabethwhoenduredourmanydinnertimeconversationsonthetopic.
“This modest-sized volume is a real treasure trove for researchers of liquid surfaces
and interfaces. Peter Pershan, a founding father and a prime motive in the field of
synchrotron X-ray studies of liquid surfaces, and Mark Schlossman, a leading expert
inthefield,presentanadmirablecombinationofacomprehensive,in-depth,exposition
oftheexperimentalmethodsandtheirunderlyingtheoryanddataanalysisapproaches,
with a lucid discussion of selected results obtained using these methods. The book’s
first part is an invaluable guide for researchers wishing to enter the field. The second
part is a broad, insightful and inspiring panorama of the field’s major achievements,
which is a joy to read, even separately from the first part. Although the selection is,
by necessity, personal, it reflects elegantly the authors’ wisdom, breadth of view, and
30yearsofexperience. Ihave nodoubt thatthisvolumewillfindaplaceofhonoron
thebookshelvesofallresearchersinthefieldworldwide.”
MosheDeutsch,Bar-IlanUniversity,Israel
“Anyone interested in learning about the physical properties of liquid surfaces will
appreciate this comprehensive treatise that emphasizes synchrotron X-ray scattering
methods. The book provides a rigorous approach to scattering theory as well as a
practicalguideonhowtoaligninstruments.PershanandSchlossmanpresentanexcellent
summaryofourcurrentunderstandingofthestructureandthermalfluctuationsobserved
at liquid interfaces with a wide range of examples extending from simple liquids to
Langmuir monolayers. There is no doubt that this will become the standard for many
years.”
BenOcko,BrookhavenNationalLaboratory
“Theliquidstateisstableinonlyasmalldomainofthespaceofdensity,pressureand
temperature,yetitplaysadominantroleinlivingandgeologicalprocessesonearth,and
inmanymanufacturingprocesses.Andeveryliquidiscontainedbyboundingmaterials
that generate interfaces with properties that are different from those in the contacting
phases.Ithasbeenrealizedfortwocenturiesthatthoseinterfacesplayseveralimportant
roles in determining phenomena in our world. However, it is only in the last three
decadesthatexperimentalmethodologyhasadvancedtothepointthattherelationships
between the atomic/molecular structure of interfaces and interfacial properties can be
studied and interpreted. Profs. Peter Pershan and Mark Schlossman, who are pioneers
inthedevelopmentofthemodernexperimentaltoolsforthestudyofliquidinterfaces,
havewrittenamasterfulaccountoftheusesofX-rayreflectionandscatteringtostudy
liquidinterfaces,andoftheinterpretationofthefindingsformanysuchinterfaces.Their
incisive treatment of the experimental methodology and the analysis of data obtained
makethisbooka“mustread”forallphysicistsandchemistsinterestedinliquidinterfacial
phenomena. This book will serve several purposes: as an introduction to the field for
graduatestudents,asareferencetothesubtletiesofinterpretationofdataforactiveusers
ofsynchrotronradiationforinterfacestudies,andasathoughtprovokingsurveyofthe
manysubtlepropertiesofliquidinterfacesandthedifferencesandsimilaritiesofthose
propertiesacrossclassesofliquidsandcontactmedia.”
StuartA.Rice,UniversityofChicago
Contents
Preface pagexi
Tablesofwidelyusedsymbols xv
1 Introduction 1
1.1 Theintrinsicliquid/vaporinterface 3
1.2 Surface-inducedorder 7
1.2.1 Surfacelayering 7
1.2.2 In-planesurfaceorder 7
1.3 Capillarywavesontheliquidsurface 9
1.4 Thinliquidfilms 15
1.5 Buriedinterfaces 16
1.6 Opticalmethods 17
1.6.1 Ellipsometry 17
1.6.2 Non-linearoptics 18
1.7 X-raysurfacemethods 20
1.8 Furtherreading 22
1.8.1 X-rayphysics 22
1.8.2 Capillarywavetheory 22
1.8.3 Softmatter 22
1.9 References 22
2 Instrumentation 29
2.1 Introduction 29
2.2 Liquid-surfacereflectometers 30
2.3 Kinematicsofscatteringfromliquidsurfacesandinterfaces 32
2.4 Overviewofthefirsttypeofliquid-surfacescatteringinstrument 34
2.4.1 Steeringcrystal:simpletracking 38
2.5 Detailedfullalignment 40
2.5.1 Opticalprealignment 40
2.5.2 X-rayalignment:firststeps 41
2.5.3 Steering-crystalalignment 42
Centeringthesteering-crystalfaceonthesynchrotronbeam 42
Equationsforthemiscutandtheeffectofη(cid:4)=0 43
viii Contents
Correctingforthemiscut 45
Correctingforη(cid:4)=0 46
2.5.4 Input-armtracking:equations 46
Equationsfortheincidentwavevectorwhenusingabtstage 47
2.5.5 Input-arm,sample-stage,andoutput-armalignment 48
Preliminaryinput-armzero 48
Input-armtrackingandsettingL 49
1
FirstsamplereflectionandsettingL andL 50
2 3
PreciseX-raydeterminationofα =0foraflatsample 53
i
Alignmentwithcurvedsamples 54
AligningtheguardslitS andsettingthezerooftheoutput-arm
2
rotation 60
2.5.6 Theoutput(detector)armforgrazing-incidencediffraction 60
Two-slitarm 60
Angular-selectionarm 62
Areadetector 63
(cid:5)
2.5.7 Reflectometermotionsasafunctionof Q 64
Q dependenceforreflectometerwithbase-tilt(bt)stage 64
z
2.6 Overviewofthesecondtypeofliquid-surfacescatteringinstrument 65
2.6.1 Practicalissuesforthesecondtypeofreflectometer 68
2.6.2 Firstvs.secondtypeofinstrument 70
2.7 Detectors 71
2.7.1 Gas-ionizationdetectors 71
2.7.2 Scintillationdetectors 72
2.7.3 Photodiodes 73
2.7.4 Position-sensitivelineardetector(PSD-1D) 74
2.7.5 Position-sensitiveareadetector(PSD-2D) 74
2.8 Absorbercalibration 77
2.9 Non-synchrotron-basedliquid-surfacereflectometers 78
2.9.1 FixedX-raysources 78
2.9.2 Butterfly-typereflectometers 80
2.10 Addenda 81
2.10.1 Braggreflection 81
2.10.2 Alignmentwithoutatiltstage 84
Equationsfortheincidentwavevectorintheabsence
ofthebtstage 84
TheQ dependenceforareflectometerwithoutabtstage 85
z
2.11 References 85
3 TheoryofX-rayscatteringfromliquidsurfaces 88
3.1 Introduction 89
3.2 Overviewofthetheory 92
3.3 Reflectionfromanidealizedflatsurface:theFresnelreflectivity 94
3.4 Reflectionfromlessidealizedsurfaces 99