Drop Impact and Spreading on Surfaces of Variable Wettability

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1、DropImpactandSpreadingonSurfacesofVariableWettabilityJ.ESprittlesY.D.ShikhmurzaevBonn2007Swansea2007MotivationDropimpactandspreadingoccursinmanyindustrialprocesses.100millioninkjetprinterssoldyearly.NEW:Inkjetprintingofelectroniccircuits.Whystudythe‘oldproblem’ofdropss

2、preadingonsurfaces?Swansea2007Worthington1876–FirstExperimentsSwansea2007Worthington’sSketchesMillimetresizeddropsofmilkonsmokedglass.Swansea2007ModernDayExperiments(mmdropsofwater)CourtesyofRomainRiobooSwansea2007Xuetal03Dropsdon’tsplashatthetopofEverest!Swansea2007R

3、enardy03etal-PyramidalDropsImpactofoscillatingwaterdropsonsuperhydrophobicsubstrates1234Swansea2007TheSimplestProblemHowdoesadropsbehaviourdependon:fluidproperties,dropspeed,dropsize,..etc?SpreadFactorApexHeightContactAngleaSwansea2007TheContactAngleInequilibriumtheang

4、ledefinesthewettabilityofasolid-liquidcombination.Howshouldwedescribeitinadynamicsituation?MoreWettable(Hydrophilic)LessWettable(Hydrophobic)Solid1Solid2Swansea2007ModellingofDropImpactandSpreadingPhenomenaTheMovingContactLineProblemConventionalApproachesandtheirDrawba

5、cksTheShikhmurzaevModelSwansea2007TheMovingContactLineProblemLiquidInviscidGasContactlineContactangleSolidSwansea2007TheMovingContactLineProblemNo-SlipImpermeabilityKinematicconditionDynamicconditionNavier-StokesContinuityContactangleprescribedNosolution!!!Swansea2007T

6、heConventionalApproachThesearetreatedseparatelyby:1)Modifyingtheno-slipconditionneartheContactLine(CL)toallowslip,e.g.2)PrescribingtheContactAngleasafunctionofvariousparameters,e.g.Onemust:1)Allowasolutiontobeobtained.2)Describethemacroscopiccontactangle.Swansea2007Exp

7、erimentsShowThisIsWrong…Canonedescribethecontactangleasafunctionoftheparameters?“Thereisnouniversalexpressiontorelatecontactanglewithcontactlinespeed”.(BayerandMegaridis06)“Thereisnogeneralcorrelationofthedynamiccontactangleasafunctionofsurfacecharacteristics,dropletfl

8、uidanddiameterandimpactvelocity.”(Sikaloetal02)Swansea2007AsinCurtainCoatingUsedtoindustriallycoatmaterials.Conventio