Thispaperisconcernedwiththedispersionofparticlesonthefluid-liquidinterface.Inapreviousstudywehaveshownthatwhensmallparticles,e.g.,flour,pollen,glassbeads,etc.,contactanair-liquidinterface,theydisperserapidlyasiftheywereinanexplosion.Therapiddispersionisduetothefactthatthecapillaryforcepullsparticlesintotheinterfacecausingthemtoacceleratetoalargevelocity.Inthispaperweshowthatmotionofparticlesnormaltotheinterfaceisinertiadominated;theyoscillateverticallyabouttheirequilibriumpositionbeforecomingtorestunderviscousdrag.Thisverticalmotionofaparticlecausesaradially-outwardlateral(secondary)flowontheinterfacethatcausesnearbyparticlestomoveaway.Thedispersiononaliquid-liquidinterface,whichistheprimaryfocusofthisstudy,wasrelativelyweakerthanonanair-liquidinterface,andoccurredoveralongerperiodoftime.Whenfallingthroughanupperliquidtheparticleshaveaslowervelocitythanwhenfallingthroughairbecausetheliquidhasagreaterviscosity.Anotherdifferencefortheliquid-liquidinterfaceisthattheseparationofparticlesbeginsintheupperliquidbeforetheparticlesreachtheinterface.Therateofdispersiondependedonthesizeoftheparticles,thedensitiesoftheparticleandliquids,theviscositiesoftheliquidsinvolved,andthecontactangle.Forsmallparticles,partialpinningandhysteresisofthethree-phasecontactlineonthesurfaceoftheparticleduringadsorptiononliquid-liquidinterfaceswasalsoimportant.Thefrequencyofoscillationofparticlesabouttheirfloatingequilibriumincreasedwithdecreasingparticlesizeonbothair-waterandliquid-liquidinterfaces,andthetimetoreachequilibriumdecreasedwithdecreasingparticlesize.Theseresultsareinagreementwithouranalysis.
