Itiswellknownthatsurfaceroughnesshasaveryimportanteffectonsuperhydrophobicity.TheWenzelandCassie-Baxtermodels,whichcorrespondtothehomogeneousandheterogeneouswettingrespectively,arecurrentlyprimaryinstructionsfordesigningsuperhydrophobicsurfaces.However,theparticulardropshapethatadropexhibitsmightdependonhowitisformed.Awaterdropcanoccupymultipleequilibriumstates,whichrelatetodifferentlocalminimalenergy.Insomecases,bothequilibriumstatescanevenco-existonasamesubstrate.Thustheapparentcontactanglesmayvaryandhavedifferentvalues.WediscusshowtheWenzelandCassie-Baxterequationsdeterminethehomogeneousandheterogeneouswettingtheoretically.Contactangleanalysisonhierarchicalsurfacestructureandcontactanglehysteresishasbeenputspecificattention.Inparticular,westudytheenergybarrieroftransitionfromCassie-BaxterstatetoWenzelstate,basedonexistingachievementbypreviousresearchers,todeterminethepossibilityofthetransitionandhowitcanbeinterpreted.Ithasbeendemonstratedthatsurfaceroughnessandgeometrywillinfluencetheenergyrequiredforadroptogetintoequilibrium,nomatteritishomogeneousorheterogeneouswetting.
