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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