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1、j45915ColloidsandMicrocapsulesAvarietyofindividualcolloidalmicroparticles(sphericalandanisotropic,solidandhollow,syntheticandbiological,fabricatedandassembled)andtheirarraysonsurfaceshavebeenapopularsubjectforAFMstudiessincetheearliestdays.AFMimaginginboth
2、dryandwetstatesallowsonetoaddresssuchfundamentalissuesastheaccuratemeasurementofcolloidalmicroparticledimensionsandtheirsizedistribution,surfacequalityandthepresence,distribution,anddensityofadsorbedmolecules,surfacecoverageofadsorbedmicroparticles,mechani
3、calandadhesivepropertiesofmicroparticles,microparticleadhesiontothesupportingsurfaces,shellthicknessofmicrocapsulesandtheirdeformationalproperties,andtheadhesionbetweenmicroparticles.Thesetopicswillbeconsideredinthischapter.Becausethecharacteristicdimensio
4、nsofthesecolloidalstructuresareusuallyonthemicroscopicscale(fromseveralmicrometerstotensofmicrometers),adequateAFMvisualizationtoobtainthefinedetailsoftheirmorphologiescanbedoneunambiguouslywithconventionalmidresolutionAFMimagingintappingmode.However,ifthei
5、rsizesarepushedtothelowerlimit,usuallybelow50nm,aseveretipdilationeffectisobservedthatmightcompletelydistortthetopographyofcolloids.InAFMimages,stillcommonlyobserved,allsuchnanoparticleslookalike,represent-inganinverseAFMtipshapethatdisregardstheoriginalsh
6、apeanddimensionsofthenanoparticles.Forsuchsmallobjects,acharacteristicaveragedimensionanditsdistributioncanstillbeobtainedfromthemeasurementsoftheverticaldimensions(which,inthecaseofsphericalparticles,representatruediameter)andatruesurfacecoveragecanbeesti
7、matedfromdirectcountingofthenumberofparticlesperspecificsurfacearea.SeveralexamplesofAFMstudiesofsuchcolloidalpolymermicroparticlesandnanoparticlesofdifferenttypeswillbediscussedinthischapter.Thesecolloidalstructuresincludevariousmicroparticlesandnanopartic
8、lesrangingfromsimplesphericalobjectstothosewithcomplexshapes,fromsyntheticcolloidstocomplexbiologicalobjects,andfromsolidmicroparticlestovariousthinshellmicrocapsules(Figure15.1)[1].However,wearenotgoingtocon
