表面张力和接触角英文课件.ppt

2008讲稿-第6章θ－Contactanglebetweenliquidandsolid;θ?－Contactanglebetweengasandsolid;θ＋θ?＝180?（6－14）θ90?nowettableθ90?wettable(润湿)θ＝0?wet(完全润湿)θ＝180?完全不润湿Contactangleismeasuredintheliquid.2008讲稿-第6章Condition:1)Thesurfaceofasolidisperfectlysmooth;2)Thevapor,liquidandsolidareinequilibrium.γSA＝γSL＋γLAcosθ（6－15）Taking（6－15）to（6－13）gives：WSL＝γLA（1＋cosθ）（6－16）3.Young-Equatuin2008讲稿-第6章Forθ＝0?，WSL＝2γLA（cohesionalworkofliquid,液体的内聚功）θ＝180?，WSL＝0，完全不润湿。Noattractive(interaction)betweensolidandliquid.θ↓，WSL↑，θcanbeusedformeasuringdegreeofwetting.2008讲稿-第6章（1）contamination(污染)ofsubstanceForliquidiscontaminated→γLA↓，ForsurfaceofsolidiscontaminatedγSAandγSL↓.亲水表面4.Factorsaffectsthemeasurementofcontactangle亲油表面2008讲稿-第6章2）RoughnessofsolidsurfaceTherealsolidsurfaceisnotperfectlysmooth.Roughnessfactor(粗糙度）（r）：Ratioofthereal(真实)surfaceareaofasolidtotheapparent(表观)surfaceareaofthesolid.r12008讲稿-第6章Forasolidsurfacewithroughnessfactorr,theYoungequationisgivenr（γSA－γSL）＝γLAcosθ?（6－17）θ?－apparentcontactangle，comparing（6－17）with（6－15）gives（6－18）2008讲稿-第6章FromEq.(6-18)itwillbeA．Forθ90?，θ?θ，aroughsurfaceofasolidismorewettablethanasmoothsurfaceofthesolid.B．Forθ90?，θ?θ，aroughsurfaceofasolidislesswettablethanasmoothsurfaceofthesolid.C．measurementofθisverydifficult.θ↓，errorsofmeasurement↑.2008讲稿-第6章5.Advancing(前进)andReceding(后退)ContactangleAdvancingcontactangle(θa):largervalueRecedingcontactangle(θr):smallervalueBothadvancingandrecedingcontactanglesshouldbemeasured.2008讲稿-第6章(θa)-Thetilted(倾斜的)plateis