MPhil Report Draft Abstract Background Contact Angle.docx

MPhil Report Draft Abstract Background Contact Angle.docx

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MPhilReportDraftAbstractBackgroundContactAngle

CambridgeUniversity

M.Phil.–Micro-andNanoTechnologyEnterprise

DepartmentofMaterialsScience&Metallurgy

SurfaceAcousticWave（SAW）andElectrostaticNanopumps

Submittedby:

MichaelSwanwick

DateSubmitted:

26thJuly2007

CourseAdvisor:

Dr.A.Flewitt

Acknowledgements

IwouldfirstliketothankmyresearchadvisorDr.AndrewFlewittforhishelpandguidanceonmyMPhilprojectandalso,Dr.YongQuinFuforhishands-onhelpwitheverythingfromfabricationtoexperimentalset-up.Myprojectwouldnothavebeensuccessfulwithouthishelp.Lastly,IwouldthanktheotherPhDstudentsinDr.Flewitt’sETRIgroupincludingNoraStaack,XiaoyeDu,andSwee-ChingTan.

TableofContents

ListofFiguresiii

ListofChartsiii

ListofEquationsiv

Abstract5

1.Introduction6

2.Background7

2.1ContinuousFlowMicropumps7

2.1.1Electrohydrodynamic（EHD）Micropumps7

2.1.2Electro-osmotic（EO）Micropumps8

2.1.3MagnetohydrodynamicMicropumps8

2.2Droplet/DigitalMicropumps8

2.2.1Surfaceacousticwaves（SAW）Micropumps9

2.2.2Dielectrophoretic（DEP）LiquidActuation14

2.2.3Electrowetting-basedActuation16

2.2.4ElectrostaticMicropump21

2.3DigitalMicromixing25

2.4MaterialSelection26

2.5BackgroundConclusion27

3.DropletContactAngleandSlidingForcexx

3.1ContactAngleIntroductionxx

3.2ContactAngleBackgroundxx

3.3ContactAngleExperimentalSet-upxx

3.4HydrophobicCoatingResultsxx

3.5ContactAngleandSlideForceDiscussionxx

3.6ContactAngleConclusionxx

4.SurfaceAcousticWave（SAW）BasedMicro-pumpxx

4.1SAWIntroductionxx

4.2SAWBackgroundxx

4.3SAWExperimentalSet-upandDeviceFabricationxx

4.4SAWDropletMixingResultsxx

4.5SAWDropletMovementResultsxx

4.6SAWTemperatureEffectsResultsxx

4.7SAWConclusionxx

5.ElectrostaticBasedMicropumpxx

5.1ElectrostaticMicropumpIntroductionxx

5.2ElectrostaticFabricationProcessFlowandMaskDesignxx

5.3ElectrostaticMicropumpSet-upxx

5.4ElectrostaticMicropumpResultsandDiscussionxx

5.5ElectrostaticMicropumpConclusionxx

6.Conclusionxx

Sourcesxx

ListofFigures

Figure1–MetalFingeronITDSurfaceofSAWMicropump9

Figure2–IndependentDropletMovementandDropletMixing11

Figure3–ComparisonofFlowVelocityvs.RF-Power12

Figure4–MixingEfficiencyandTemperaturevs.AppliedVoltageforSAWMixer13

Figure5–FresnelAnnularRingAcousticWaveMicropump14

Figure6–DielectrophoreticLiquidActuation15

Figure7–AsymmetricActuationofDropletbyElectricField16

Figure8–InterfacialEnergiesofDroplet17

Figure9–Electrowetting（EWOD）DropletActuator18

Figure10–DesignOptionsforElectrowettingDropletActuator19

Figure11–AsymmetricDropletMovingbyEWODMicropump19

Figure12–CartoonofEWODMicropump20

Figure13–Box-in-boxElectrodes21

Figure14–DesignStudyforCompleteEWODDevice21

Figure15–PrincipleofElectrostaticDigitalActuation22

Figure16–ElectrostaticActuationMethod23

Figure17–DaughterDropletFormationbyElectrostatics24

Figure18–NovelElectrostaticDropletActuationTechnique24

Figure19–TimeofMixingvs.SpeedofDroplet26

Figure20–MicrocontactPrintingforEWODDevices27

Figure21–Contactmechanicsfora）Young’sMode,b）Wenzel’sMode,c）Cassie’sMode,d）MixofWenzel’sandCassie’sMode33

Figure22–SuperhydrophobicCross-grownCNTs162°ContactAngle34

Figure23–CartoonofWaterDropletonSlope35

Figure24–ExampleofPTFEonZnOwith60μlDropletatSlidingAngle37

Figure25–60μlDropletonUntreatedLiNbO3a）Flat（left）andb）SlidingSlope（right）37

Figure26–60μlDropletonPTFETreatedLiNbO3a）Flat（left）andb）SlidingSlope（right）37

Figure27–ContactAngleonFlatSurfacefor60μlDroplet38

Figure28–SlidingSlopefor60μlDroplet39

Figure29–HysteresisattheSlidingAnglefor60μlDroplet39

Figure30–SlidingForce,Fs,fora60μlDIWaterDroplet40

Figure31–ContactAngleof10μlDropletandPTFEHardBakedat300°Cfor25min41

Figure32–ContactAngleof10μlDropletonPTFEa）Flat（left）b）SlidingSlope（right）41

Figure33–MassloadingbetweenIDTsforBiosensorApplication47

Figure34–SAWdevicesample（left）andexperimentalsetup（right）49

Figure35–ReflectionandTransmissionofLiNbO3SamplewithandwithoutPTFE49

Figure36–CartoonofSAWLeakywaveandRayleighAngle50

Figure37–DropletStreamingVorticesfromSAWdevicea）TopViewb）SideView51

Figure38–ExampleofDropletStreamingatapproximately5VonUntreatedLiNbO351

Figure39–DropletStreamingVelocityvs.VoltageforUntreated&ParaffinTreatedSample52

Figure40–DropletVelocityonPTFEandDowCorning704oiltreatedLiNbO353

Figure41–SurfaceTemperatureEffectsforλ=32μmSAWdevice54

Figure42–SurfaceTemperatureEffectsforλ=64μmSAWdevice55

Figure43–ChevronDesignofElectrodes56

Figure44–DropletMovementbyElectrostaticActuation57

Figure45–AutoCADDrawingsofElectrostaticMicropumpMaskDesign57

Figure46–ContactAngleandSlidingSlopewithSU-8andPTFE200°CHard-bake61

Figure47–ContactAngleandSlidingSlopewithSU-8andPTFE250°CHard-bake61

Figure48–ComparisonofSlidingForcefor60μlDropletwithDifferentSurfaceTreatments62

Figure49–ProfilesofPTFEonSU-8surface250°C（left）and200°C（right）63

ListofTables

Table1–PTFEThickness36

Table2–Datafrom60μlDIWaterDropletonDifferentSurfacesandAngles37

Table3–ContactandSlidingAngleforVaryingSizeDIWaterDroplets41

Table4–Xxx

ListofEquations

Equation1–Stuetzer’sformula7

Equation2–VelocityEquationforElectro-osmoticFlow8

Equation3–LorentzForceEquation8

Equation4–SAWDrivingFrequency10

Equation5–RayleighDeflectionAngle10

Equation6–PressurefromAcousticRadiation10

Equation7–PecletNumber12

Equation8–DEPDrivingForce14

Equation9–VoltageforDEPActuation14

Equation10–Lippman’sEquation17

Equation11–Young’sEquation17,32

Equation12–Wenzel’sEquation32

Equation13–Cassie’sEquation33

Equation14–EquationforSphericalDropletVolumewithContactPatch17

Equation15–SlidingForce17

Equation16–ForcefromGravity17

Equation17–Xxx

SurfaceAcousticWave（SAW）andElectrostaticNanopump

Abstract

Thefieldofmicrofluidicisdevelopingrapidlywithemergingproductssuchasmicrototalanalysissystem（μTAS）andmicro-coolingdevicesthatrelyonmicropumpsasthecoreoftheirfunction.Micropumpshaveevolvedfromsimplysmallerversionsofmacro-pumpsandnowtakeadvantageofuniquepropertiesthataredominantonthemicronandnanometrescale.Micropumpsaredividedintomechanicalandnon-mechanicaldesignswithnon-mechanicalpumpsbeingfurthersubdividedintocontinuousflowanddropletbaseddevices.Theprojectfocusesthreekeyareastwochannel-lessnon-mechanicaldigitalordropletbasedmicropumps:

surfaceacousticwave（SAW）andelectrostatic,andthehydrophobiccoatingneededdropletmovement.

TheSAWdeviceshaveanaluminiumInterDigitalTransducers（IDTs）ontheLithiumNiobate（LiNbO3）piezoelectricmaterialthatactsastheexcitationagent.WhenthesignalthroughtheIDTmatchesthecorrectfrequency,amechanicalwavepropagatesawayfromtheIDTonthesubstratesurface.TheRayleighwavescauseanacousticradiationpressurefromtheretrogradeellipticmotion.TheprojectfocusesonthesurfacetreatmentandhydrophobicityofthesurfaceusingPolytetrafluoroethylene（PTFE）andtheeffectonsurfaceenergyandforceneedtomoveadroplet.TheresultsshowdropletmixingandmovementasafunctionofsurfacetreatmentandappliedvoltageandsurfacetemperatureeffectsfromtheSAWdevice.

Theelectrostaticpumpisbasedontheconceptofelectro-wetting.Adiscreetdropletismovedbydeformingtheliquidasymmetrically.Thisformsapressuregradientinthedropletwhichcausesmovement.Thedeformationiscausedbyactivatinganelectrodeslightlytoonesideofthedroplet.Ifthecapillaryforcesthatkeepitinplaceareovercome,thedropletmovestowardtheelectrode.Anotherwaytodescribethemotionisthattheelectrodewetsthesurfaceaboveit.Thiscreatesahydrophilicgradientwhichthedropletmovesalong.Fortheproject,fivedeviceshavebeendesignedincludingastraightlinemotion,oval‘racetrack’,dropletmixer,dropletdirection,anddropletsplitterwithtwodifferentelectrodepitches.Theresultswillshowhowfrequencyandvoltageaffectdropletmovementalongwithsurfacetreatment.

1.Introduction

Needstobewritten.

2.BackgroundofMicro-pumps

Nano/micropumpshavedevelopedoverthelast30yearsinparallelwiththeadvancementofmicroelectromechanicalsystems（MEMS）technology.Micropumpsareutilizedinmanyapplicationsincludingbiological,chemical,andsensorsystems.Byreducingtheliquidvolume,experimentsreducewaste,providefasterreactions,quickenmixingtimeandpotentiallyprovideasaferworkenvironment.Anearlyapplicationofthemicropumpwasaninsulindeliverysystemwherepreciseflowratecontrolisimportant[1].OtherexamplesincludinguseinbioassaysforDNAdetectionandmicro-coolinghotspotsonmicroprocessorchips[2].In2002,themicrofluidicsmarketwasestimatedat$3-4.5billionandisincreasing25-35%annually[3].Anewfieldofresearchandproductscalledmicrototalanalysissystem（μTAS）isemergingthatreliesonmicropumpsforlab-on-chipdevices[4].Currently,thissystemandothermicrofluidicapplicationsareinlimiteduseduetothehighcostofproductionandlac