简介：Manystudieshaveinvestigatedevaporationofsessiledropsinanattempttounderstandtheeffectofwettingontheevaporationprocess.Recentlyinteresthasalsoincreasedinthedepositionofparticlesfromsuchdrops,withevaporativemassfluxbeingdeemedtoberesponsibleforring-likedeposits,andcounteractionofthemassfluxbyMarangoniconvectionexplainingmoreuniformdepositionpatterns.Understandingofsuchdepositionprocessesisimportantinbiologicalapplications,suchastheLitostest-systemendorsedbytheRussianMinistryofHealthfordiagnosisofurolithiasisandtheevaporationofcolloidaldropsfordepositingandorganizingproteinsandDNA.Inmostcaseswheredepositionfromevaporatingdropshasbeenstudied,velocityinformationisinferredfromthefinaldepositionpatternorfrommathematicalmodelingbasedonsimplifiedmodelsofthephysicsoftheevaporationprocess.Inthisstudywehavedirectlymeasuredtheflowvelocitiesinthebaseofsessiledrops,usingmicroparticleimagevelocimetry,viewingthedropfrombelow,throughthecoverslide.Forwaterdrops,aradialpatternofflowwasobservedwithamaximumvelocityclosetobutnotatthepinnedouteredge.For‘azeotropic’ethanol/watermixtures,thevelocityfieldismorechaotictobeginwith,passingthroughaphaseinvolvingthreeorfourrecirculationcellsandfinallyhavingthesameradialpatternasforwaterdrops.