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1、TEXTONEWilliamIlliamMorris(thewallpaperdesigner,ratherthanthecarmaker)suggestedthatnothingshouldhaveaplacethatisnotknowntobeusefulorbelievedtobebeautiful.Opals,though,mightbeboth.AgroupofresearchersfromtheUniversityofSouthampton,inEngland,andtheGermanPlastic
2、sInstituteinDarmstadt,ledbyJeremyBaumberg,havediscoveredhowtocreateaplasticwiththegemstone'siridescentproperties.Theirinventioncouldbeusedtomakeasparklingsubstituteforpaint,banknotesthatarehardtocounterfeitandchemicalsensorsthatcanactasvisiblesell-bydates.Op
3、alsgettheirmilkysheenandrainbowsparklefromthewaylightisscatteredbythetinycrystalsthatformthem.Thesecrystalsarestackedinwhatisknownasaface-centredcubicstructure.Thismeansthattheconstituentatomsarearrangedinalatticeofcubes,withoneextraatomsittingatthecentreofe
4、achcube'ssixfaces.Lightenteringthislatticegetsbouncedaroundinwaysthatgeneratecolourbyreinforcingthepeaksofsomewavelengthsandcancellingoutthoseofothers.Formanyyearsresearchershavebeentryingtodevelopasyntheticmaterialwiththesamelight-scatteringpropertiesasanop
5、al,byetchingpatternsintovariousmaterials.Thatapproachhasfailed.Instead,DrBaumberghasbuilthisopalescentmaterialfromscratch.Heandhisteamgrewtinypolystyrenespheresuntiltheyweresome200nanometresacross,beforehardeningthemwithablastofheat.Theythencoatedthespheresw
6、ithastickypolymerbeforeheatingthemagain.Asthemixturewasbaked,thespheresmovednaturallyintoaface-centredcubicstructure.Theresultisaflexiblefilmofcrystalswithopalescentpropertiesthatcanbeusedtocoatmalleablesurfaces,producingattractiveiridescenthues.Thesizeofthe
7、spherescanbetailoredtoscatterparticularwavelengthsoflight—ausefulpropertyforsecurityapplicationsinwhichitisimportantthatmaterialscanbeidentifiedprecisely.Moreover,whenthefilmiswarped,thespacesbetweenthecrystalschange—andthecoloursproducedchangewiththem.These
8、twopropertiesmakeopalescentfilmanobviousmaterialforcurrency.Banknotescontainingitwouldproducedistinctivecolourswhenstretched,unlikecounterfeitsmadefromothermaterials.Tousethefilmtodetectfoodspoi
