NANOYOU Teachers Training Kit in Nanotechnologies ... B1_Teacher Teachers Training Kit in Nanotechnologies Experiment B ... Teachers Training Kit in Nanotechnologies for ... optical properties of crystalline solids. ...

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<ul><li><p>NANOYOUTeachersTrainingKitinNanotechnologies</p><p>ExperimentB LiquidCrystalsExperimentModule</p><p>WrittenbyLuisaFilipponiInterdisciplinaryNanoscienceCenter(iNANO)AarhusUniversity,DenmarkJanuary2010CreativeCommonsAttributionShareAlike3.0unlessindicatedotherwiseintextorfigurecaptions.ThisdocumenthasbeencreatedinthecontextoftheNANOYOUprojectaspartofWP4Task4.1.Allinformationisprovidedasisandnoguaranteeorwarrantyisgiventhattheinformationisfitforanyparticularpurpose.Theuserthereofusestheinformationatitssoleriskandliability.Thedocumentreflectssolelytheviewsofitsauthors.TheEuropeanCommissionisnotliableforanyusethatmaybemadeoftheinformationcontainedtherein.</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page2of18</p><p>MATERIALINCLUDEDINTHISEXPERIMENTPACKAGE:</p><p>Forteachers:</p><p>TEACHERRESOURCESFOREXPERIMENTB</p><p>Forstudents:</p><p>EXPERIMENTBSTUDENTBACKGROUNDREADING</p><p>EXPERIMENTBSTUDENTSYNTHESISPROCEDURE</p><p>EXPERIMENTBSTUDENTLABORATORYWORKSHEET</p><p>LEVELOFEXPERIMENT:Medium</p><p>DISCLAIMER:Theexperimentsdescribed inthe followingtrainingkitusechemicalswhichneedtobeusedaccordingtoMSDSspecifications.Personalprotectionmustbetakenasindicated.Aswithallchemicals,useprecautions.Solidsshouldnotbeinhaledandcontactwithskin,eyesorclothingshouldbeavoided.Washhandsthoroughlyafterhandling.Disposeas indicated. All experiments must be conducted in the presence of an educator trained for science teaching. Allexperiments will be carried out at your own risk. Aarhus University (iNANO) assumes no liability for damage orconsequentiallossessustainedasaresultofthecarryingoutoftheexperimentsdescribed.</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page3of18</p><p>TEACHERRESOURCESEXPERIMENTB:LIQUIDCRYSTALSAIM: Liquid crystals (LCs) are an exampleof selfassembledmolecules that are sensitive to externalfactors,suchastemperature,andthatchangetheirassemblyasaconsequenceofthesevariations.Theeffect insometypesofLCsisachangeofcolour.Thisexperimentwillshowstudentstwofundamentalconcepts:1.Thewayamaterialbehavesat themacroscaledependson itsstructureat thenanoscaleand2.AtthenanoscaleLCsareselfassembledmoleculesthatorganisethemselvesintonanostructureswhichhavespecificopticalproperties.FIELDOFNANOTECHNOLOGYAPPLICATION:FundamentalconceptsinnanoscienceEXTRA TEACHERS READING: Chapter 5 Overview of nanomaterials in Module 1 of NANOYOUTeachersTrainingKitinNanotechnologiesREQUIREDSTUDENTPREKNOWLEDGE:Electromagneticradiation,colourandabsorbanceConceptofselfassemblyConceptofchiralitySTUDENTREADING:NANOYOUStudentsbackgrounddocumentforExperimentBEXPECTEDOUTCOME:UnderstandingofconceptofselfassemblyUnderstanding that thewayamaterialbehavesat themacroscale isaffectedby itsstructureat thenanoscaleLearnaboutliquidcrystalsandhowtheyworkTestarealthermotropicliquidcrystalandseehowitscolourchangeswithtemperatureCreatealiquidcrystalthermometerSTUDENTASSESSMENT:NANOYOUExperimentBStudentlaboratoryworksheet</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page4of18</p><p>BACKGROUNDINFORMATIONSelfassemblyTheconceptofselfassemblyderivesfromobservingthat,innaturalbiologicalprocesses,moleculesselfassembletocreatecomplexstructureswithnanoscaleprecision.ExamplesaretheformationoftheDNAdouble helix or the formation of themembrane cell from phospholipids. In selfassembly, subunitsspontaneously organise and aggregate into stable, well defined structures through noncovalentinteraction.Thisprocessisguidedbyinformationthatiscodedintothecharacteristicsofthesubunitsand the final structure is reachedbyequilibrating to the formof the lowest freeenergy.Anexternalfactor,suchasachangeintemperatureorachangeinpH,candisruptthisorganisation.Forinstance,aprotein selfassembles in a specific structure,but if exposed to conditions such ashighheatorhighacidity,itcandenature,whichmeansthatitsstructureisdamaged,andtheproteinunfolds.Thismeansthat theprotein loses its functionas its structure isdamaged. So inNature selforganised structureshavespecificfunctions.Molecules inNaturechangeconformationandmovefromoneselforganisedstructure intoanotherastheybindtocertainionsoratoms.Alotofexamplescanbegiven,likehaemoglobulin(whichcapturesandreleasesanironion),orthepotassiumsodiumpump,chlorophyll,etc.In this experiment studentswill see an exampleof a selfassembledmacromolecule, a liquid crystal.Liquidcrystalshavepropertiesthataredirectlyconnectedtothewaytheirlongmoleculesselfassembleintonanostructures.Althoughwecannotseethesewithournakedeye,wecanseemacroscalechangesin the optical properties (colour) of the liquid crystal as its temperature is changed. When thetemperatureofa liquid crystal changes, itsmolecules selfassemble inadifferentnanostructure,andthis influences theway light is reflectedby the liquid crystal, so that adifferent colour isobserved.Thereforethiscolourchangeisadirectconsequenceofachangeintheselforganisationoftheliquidcrystalmolecules.</p><p>Whatisaliquidcrystal?</p><p>Aliquidcrystalisafourthstateofmatter:ithaspropertiesbetweenthoseofaconventionalliquidandthoseofasolidcrystal.Liquidcrystalsarepartlyorderedmaterials,somewherebetweentheirsolidandliquidphases.ThismeansthatLCscombinethefluidityofordinaryliquidswiththeinterestingelectricalandopticalpropertiesofcrystallinesolids.</p><p>Liquidcrystalsaretemperaturesensitivesincetheyturn intosolid if it istoocoldand into liquid if it istoohot.Thisphenomenoncan,forinstance,beobservedonlaptopscreenswhenitisveryhotorverycold.</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page5of18</p><p>Figure 1. Example of the selforganisation ofanisometric (i.e., with asymmetrical parts)molecules in liquidcrystalline phases. On the left:rodlikemolecules form a nematic liquid, inwhichthe longitudinal axes of themolecules are alignedparallel to a common preferred direction("director"). On the right: disclike (discotic)moleculesarrange tomoleculestacks (columns), inwhichthelongitudinalaxesarealsoalignedparallelto the director. As a result of their orientationalorder, liquid crystals exhibit anisotropic physicalproperties, just like crystals. (Image Credit:http://www.ipc.unistuttgart.de/~giesselm/AG_Giesselmann/Forschung/Fluessigkristalle/Fluessigkristalle.html)</p><p>Figure2. Schematic representationofmolecules in a solid (left,molecules are well organised), in a liquid crystal (centre)moleculeshavealongrangedistanceorder)andinaliquid(right)molecules are not ordered. (Image credit: Copyright IPSEEducationalResources,UniversityofWisconsinMadison)</p><p>Themoleculesinaliquidcrystalareoftenshapedlikerodsorplatesorsomeotherformsthatencouragethemtoaligncollectivelyalongacertaindirection(Figure1).</p><p>Aliquidcrystalisformedbytheselfassemblyofmoleculesinorderedstructures,calledphases.</p><p>Anexternalperturbation,suchasachangeintemperatureormagneticfield,evenverysmall,caninducetheLCstoassumeadifferentphase.Themoleculesinliquidcrystaldisplaysforinstancearereorientedby relatively weak electrical fields. Different phases can be distinguished by their different opticalproperties(Figure2).</p><p>Liquidcrystals(LCs)aredividedintothreegroups:</p><p> Thermotropic LCs: they consist of organicmolecules, typically having coupled double bonds, andexhibitaphasetransitionastemperatureischanged(Figure3,left) Lyotropic LCs: they consist of organicmolecules, typically hydrophilic (waterloving) and exhibit aphasetransitionasafunctionofbothtemperatureandconcentrationoftheLCmolecules inasolvent(typicallywater)(Figure3,right)</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page6of18</p><p>Figure3.(Left)chemicalstructureof N(4Methoxybenzylidene)4butylaniline (MBBA); (Right):Structure of lyotropic liquidcrystal: 1 is a bilayer and 2 is amicelle. The red heads ofsurfactant molecules are incontactwithwater,whereas thetails are immersed in oil (blue).(Image credit: Wiki commons,Creative Commons AttributionShareAlike3.0).</p><p>MetallotropicLCs:theyarecomposedofbothorganicandinorganicmolecules,andtheirLCtransitiondepends not only on temperature and concentration, but also on the organicinorganic compositionratio.</p><p>Lyotropic liquidcrystallinephasesareabundant in living systems, suchasbiologicalmembranes,cellmembranes,manyproteins(liketheproteinsolutionextrudedbyaspidertogeneratesilk),aswellastobaccomosaicvirus.Soapisanotherwellknownmaterialwhichisinfactalyotropicliquidcrystal.Thethicknessofthesoapbubblesdeterminesthecoloursoflighttheyreflect.</p><p>In this experimentmodule, the students will study the properties of a thermotropic liquid crystalmeaningthatitspropertieschangewithchangesintemperature.</p><p>Liquidcrystalsthatchangecolourwhentemperatureischanged</p><p>Liquidcrystalphasesthatrespondtocertaintemperaturerangesarecalledthermotropicphases.ManythermotropicLCsexhibitavarietyofphasesastemperature ischanged,as illustrated inFigure4.Theordering inside a thermotropic liquid crystal exists in a specific temperature range. At hightemperatures, the thermalmotionwilldestroy thedelicate cooperativeorderingof the liquid crystalphase,pushingthematerialintoaconventionalisotropicliquidphase.Attoolowatemperature,mostliquidcrystalmaterialswillformaconventional(thoughanisotropic)crystal.Theseintermediatephaseshavesome leveloforder,which isprogressively lostas the temperature rises. In thesmecticphases,whicharefoundat lowertemperaturesthanthenematic,moleculesformwelldefined layersthatcanslide over one another. The smectics are thus positionally ordered in one direction. In the nematicphase,moleculeshavenopositionalorderbuttheyhavelongrangeorientationalorder.Thismeansthatthemoleculesmovequiterandomlybuttheyallpointinthesamedirection(withineachdomain).</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page7of18</p><p>Figure4.SchematicrepresentationofthestructuretransitionofathermotropicLCfromthesmetictothenematicphaseas the temperature is increased. (Imagecredit:ownworkadapted fromWikicommons,CreativeCommonsAttributionShareAlike3.0andfromIPSEEducationalresourcesliquidcrystals,UniversityofWisconsinMadison.)</p><p>Figure5.Schematicrepresentationoforderinginchiralliquidcrystalphases:achiralnematicphase (also called the cholesteric phase) in an LC (Image credit:Wiki Commons, CreativeCommonsAttributionShareAlike3.0)</p><p>What is important tonote is that some specific structuralandopticalpropertiesareassociatedwitheach LC phase: as the temperature is changed, the colour of the LCs changes. Thus changing thetemperature of thematerial allowsmoving thematerial from one phase to the other, so that thematerial exhibits these different colours. This type of liquid crystal is used in thermometers and inminiaturisedtemperaturesensors(forinstancetolocateshortcircuitsoncircuitboards).Aparticulartypeofliquidcrystalphaseisthechiralnematicphase.Thechiralnematicphaseexhibits chirality (handedness).Thisphase isoften called thecholestericphasebecause itwasfirstobservedforcholesterolderivatives. Inthisexperimentstudentswillanalysethistypeofliquidcrystal(Figure5).</p><p>Only chiralmolecules (i.e., those that lack inversion symmetry) cangive rise to suchaphase. In thisphase,themoleculesarestackedinrotatinglayers,likeaspiralstaircase(helix).Ineachstepofthestaircasethemoleculesarearrangedinaspecificorder,butthereisafiniteanglebetweeneachstepandthenext(Figure6).</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page8of18</p><p>Figure7.RepresentationofapitchchangeinachiralLCasthetemperatureischanged.Imagecredit: Image adapted from IPSE EducationalResources (Liquid crystals), University ofWisconsinMadison).</p><p>Figure 6. (Left): Schematic representations of stackedrotating layers in a chiral LC forming a spiral staircasehaving a pitch p. (Right) schematic representation of thepitch in a chiral LC (Images credit:Wiki commons,CreativeCommonsAttributionShareAlike3.0).</p><p>Thechiralpitch,p,referstothedistanceoverwhichtheLCmoleculesundergoafull360twist.Asthetemperatureoftheliquidcrystalchanges,thepitchchanges,whichleadstotighterorlooserhelixes.</p><p>Whatgivesthecolourtotheliquidcrystal?Whenlightstrikesaliquidcrystal,someofthelightisreflected.Whatweseeisthereflectedlight.Thecolour(i.e.thewavelength)ofthereflectedlightdependsonhowtightlytwistedthehelixis.Ifthepitchin the liquid crystal is of the same order as the wavelength of visible light (400700 nm), theninterestingopticalinterferenceeffectscanbeobserved.Thecolourofthelightreflecteddependsonthepitch inthe liquidcrystal,that is,onhowtightlytwistedthehelixis.Whenthehelix istightlytwisted,thepitchissmaller,soitreflectssmallerwavelengths(blueendofthespectrum);whentheliquidcrystalislesstwisted,ithasalargerpitch,soitreflectslargerwavelengths(redendofthespectrum).Anincreaseintemperatureleadstoadecreaseinthepitch.Byincreasingthetemperatureoftheliquidcrystal one should expect a colour change from the red end of the spectrum to the blue end of thespectrum,sofromorange,toyellow,green,blueandviolet(Figure7).</p><p>The chiral twisting that occurs in chiral LC phases alsomakes the system respond differently in right and lefthandedcircularlypolarised light.Thesematerialscan thusbeusedaspolarisationfilter.</p></li><li><p>NANOYOUTeachersTrainingKitinNanotechnologiesfor1418yearsscholars(ExperimentModule)</p><p>TheresearchleadingtotheseresultshasreceivedfundingfromtheEuropeanCommunity'sSeventhFrameworkProgramme(FP7/20072013)undergrantagreementn233433</p><p>Page9of18</p><p>WHATCANTHISEXPERIMENTTEACHABOUTNANOTECHNOLOGY?The properties ofmaterials at themacroscale are affected by the structure of thematerial at thenanoscale. Changes in a materials molecular structures are often too small to see directly, butsometimeswecanseechangesinthematerialsproperties.Liquidcrystalsareanexcellentexample,inparticular the typeused in thisexperiment, since itsopticalproperties (colour) change visiblyas thetemperature of the liquid crystal is changed. In nanotechnology, scientists take advantage of thepeculiarpropertiesofmaterialsatthenanoscaletoengineernewmaterialsanddevices.Liquidcrystalsareanexampleofselfassembledmoleculeswhichchangetheirspatialorganisationindependenceofexternalfactorssuchastemperature.Selfassemblyisanotherfundamentalconceptinnanoscience.</p><p>THISEXP...</p></li></ul>

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