How to Select Nanomaterials.docx
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How to Select Nanomaterials.docx
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HowtoSelectNanomaterials
HowtoSelectNanomaterials
SilverNanopowder.ImageCredit:
SkySpringCarbonnanotubes.ImageCredit:
RSC
Nanomaterialshavefeaturesorparticlesizesintherangeof1to100nm.Theycanbenaturalormanmadeandtheyhaveawidevarietyofapplications
WhatareNanomaterials?
Nanomaterialsarematerialspossessingoneormoredimensionalfeatureshavingalengthontheorderofabillionthofameter,or10-9,tolessthan100billionthsofameter.Toillustratethissize,thereare25,400,000nanometersinaninchandonacomparativescale,ifamarblewereananometer,thanonemeterwouldbethesizeoftheearth.
NanotechnologyDescription
Thetermnanomaterialincludesallnanosizedmaterials,includingmaterialsthatcanbeengineeredorfoundinnature.Theyareimportantbecausetheyexhibituniquepropertiesbecauseofthesizeoftheirfeaturesandscientistsandengineershavelearnedhowtomanipulateandunderstandtherelationshipoftheirpropertiestosize.TheNationalNanotechnologyInitiative(NNI)websiteputstheseideasinasimplephrase,"Atthenanoscale,thephysical,chemical,andbiologicalpropertiesofmaterialsdifferinfundamentalandvaluablewaysfromthepropertiesofindividualatomsandmoleculesorbulkmatter."
NanoScale.ImageCredit:
Nano.gov
Recentdiscoveriesinareassuchasmicroscopyhavegivenscientistsandengineersnewtoolstoobserveandmanipulatethephenomenathatoccurwhenmatterisorganizedatthenanoscalelevel.Thescanningtunnelingmicroscope(STM)andtheatomicforcemicroscope(AFM)havemadenanotechnologypossibletoenablescientiststoutilizetheuniquephysical,chemical,mechanical,andopticalpropertiesofmaterialsthatnaturallyoccuratthatscale.Nanomaterialsfallunderthefieldofnanotechnologyandtheeventsthatoccuratthenanoscalelevelarebasedon"quantumeffects"andphysicaleffectssuchasexpandedsurfacearea.
HowAreNanomaterialsMade?
'Nanomaterials'isatermthatincludesallnanosizedmaterials,includingengineerednanoparticles,incidentalnanoparticles,andnano-objectslikethosethatexistinnature.Nanomaterialsexistinnatureintheformofbiologicalmaterialsorabyproductofhumanactivities.Forinstance,hemoglobinis5.5nanometersindiameterandbiologicalionchannelscanbeassmallasafewtenthsofananometer.Naturalnanomaterialssuchassmokefromfireandseasprayexistintheairaroundus.Manmadenanomaterialbyproductsincludeautomobileexhaustandweldingfumes.Scientistshavealreadycopiedthenanostructureofseveralnaturalitemsincludingthelotusleavetocreatewaterrepellentsurfacesbeingsusedtomakestainproofclothingandspidersilk,whichisnaturallyreinforcedwithNanoscalecrystals.
Nanomaterialscanalsobeengineeredandaremadethroughaprocesscallednanomanufacturing.Nanomanufacturinghastwobasicapproaches.
∙Bottom-upbuildsproductsbybuildingthemupfromatomic-andmolecular-scalecomponents.Theprocessinvolvesmanipulationorsyntheticmethodsofbiochemistryindirectassemblingsubnanoscalebuildingblocks,suchasatomicmolecularandsupramolecularelementsintorequirednanoscalepatterns.Itcanbeaverytimeconsumingprocessandisthereforebetterforbiomedical,chemicalandphysicalsensorsthanlargescalemolecularelectronicsandcomputerparts.Thefabricaionstrategymustoccurinparallelorinarraystoself-formgroupsofatomsfastenoughtoproduceusefulstructuresofmacroscopicsize.Furtherresearchisbeingdonetocreateself-assemblingstructuresthatwillputthemselvestogetherandreducethewasteoftop-downapproaches.Currently,thebestbottom-upapproachisnano-manipulationwhichallowsforprecisecontroloversingleatomsandnanoscaleparticlesfortheformationofnanostructures.
∙Top-downreduceslargepiecesofmaterialstotheNanoscalelevel.Theprocesshasevolvedfromlithographictechniques,requiringlargeramountsofmaterialswhichcanleadtowastefromthediscardingofexcessmaterial.Anotherdifferencefromthebottomupapproachisthatinthetop-downapproach,thepartsorchipsarebothpatternedandbuiltinplacesothatnoassemblystepisneeded.Itisaveryusefulprocessfortheevolutionoftheelectronics,computer,photonic,andmicrosystemindustries.
∙Combinedbottom-upandtop-downapproacheswillsoonbethestandardpractice.
Withinthetop-downandbottom-upcategoriesofnanomanufacturing,thereareagrowingnumberofnewprocessesthatenablenanomanufacturing.Amongtheseare:
∙Chemicalvapordeposition(CVD)isaprocessinwhichchemicalsreacttoproduceverypure,high-performancefilms.CVDinvolvesflowingaprecursorgasorgassesintoachambercontainingoneormoreheatedobjectstobecoated.Achemicalreactionoccursonorneartheheatedsurfaces,resultinginthedepos
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