Thesolid-liquidinterface：5固液界面

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1、5Thesolid-liquidinterfaceContactangleSG=SL+LGcosLLGSGSLWettingTypesofwettingSpreadingwettingAdhesionalwettingImmersionalwettingSpreadingwettingInspreadingwetting,aliquidspreadsspontaneouslyonthesolidtoformaliquidfilm.Thesolid-gasinterfacedisappearsandThesolid-liquidinterfaceandliquid-

2、gasinterfaceform.thespreadingcoefficientS=Wa-Wc=SG-SL-LGispositiveorzero.Thecontactangleshouldbezero.LAdhesionalwettingWhenaliquidcombineswithasolidasshowninthefollowingfigure,theprocessistermedadhesionalwetting.TheworkofadhesionWa=-G/A=SG+LG-SL=LG(1+cos)SSLLImmersionalwettingInimmer

3、sionalwetting,thesolid,whichisnotoriginallyincontactwiththeliquid,isimmersedcompletelyintheliquid.TheworkofadhesionWa=-G/A=SG-SL=LGcosWhen<90,immersionalwettingisspontaneous.SSLLMeasurmentofcontactanglesFactorsaffectingcontactanlgesmeasurmentContaminationoftheliquidSolidsurface(degreeo

4、fheterogeneity,impurities)AdvancingangleorrecedingangleTheextenttowhichthedropisvibrated.Dropoftheliquid/bubbletan/2=2h/dThevolumeofthedropshouldbelessthan10-4ml,or<90.dhairTilting-platemethodTheangleoftheplateequalsthecontactanglewhentheliquidsurfaceremainsperfectlyflatrightuptothesolids

5、urface.DeterminationofcontactangleofpowderPackingthepowderintoatubeMeasureingthepressure(p)requiredtopreventtheliquidinquestionfromenteringthepowder.p=2cos/rrisfoundfromasimilarexperimentusingaliquidwhichcompletelywetsthesolid.r=2’/p’Thencos=’p/(p’)Factorsaffectingcontactanglesandwetti

6、ngNatureofthesolidandliquidSurfaceroughnessThemethodusedtopreparethesolidsurfaceWettingagentsWettingagentsareusedtoadjustthewettinginmanypracticalsituations.Forexample,increasingwettingofpesticidewithplantsandinsectscanimprovetheinsecticidaleffect.Decreasingwettingoftextilefabricscanimproveth

7、ewaterrepellency.FlotationOreflotationWhenthecontactangleisbigenough,asolidwillfloatonaliquidsurface.First,thecrudeoreiscrushedandthengroundintoaslurryinwater.Asmallquantityofcollectoroilisaddedduringthegrindingage.Thecollectoroiladsorbsstron