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1、TEXTONEWilliamIlliamMorris(thewallpaperdesigner,ratherthanthecarmaker)suggestedthatnothingshouldhaveaplacethatisnotknowntobeusefulorbelievedtobebeautiful.Opals,though,mightbeboth.AgroupofresearchersfromtheUniversityofSouthampton,inEngland,andtheGermanPlasticsInstituteinDarm
2、stadt,ledbyJeremyBaumberg,havediscoveredhowtocreateaplasticwiththegemstone'siridescentproperties.Theirinventioncouldbeusedtomakeasparklingsubstituteforpaint,banknotesthatarehardtocounterfeitandchemicalsensorsthatcanactasvisiblesell-bydates.Opalsgettheirmilkysheenandrainbows
3、parklefromthewaylightisscatteredbythetinycrystalsthatformthem.Thesecrystalsarestackedinwhatisknownasaface-centredcubicstructure.Thismeansthattheconstituentatomsarearrangedinalatticeofcubes,withoneextraatomsittingatthecentreofeachcube'ssixfaces.Lightenteringthislatticegetsbo
4、uncedaroundinwaysthatgeneratecolourbyreinforcingthepeaksofsomewavelengthsandcancellingoutthoseofothers.Formanyyearsresearchershavebeentryingtodevelopasyntheticmaterialwiththesamelight-scatteringpropertiesasanopal,byetchingpatternsintovariousmaterials.Thatapproachhasfailed.I
5、nstead,DrBaumberghasbuilthisopalescentmaterialfromscratch.Heandhisteamgrewtinypolystyrenespheresuntiltheyweresome200nanometresacross,beforehardeningthemwithablastofheat.Theythencoatedthesphereswithastickypolymerbeforeheatingthemagain.Asthemixturewasbaked,thespheresmovednatu
6、rallyintoaface-centredcubicstructure.Theresultisaflexiblefilmofcrystalswithopalescentpropertiesthatcanbeusedtocoatmalleablesurfaces,producingattractiveiridescenthues.Thesizeofthespherescanbetailoredtoscatterparticularwavelengthsoflight—ausefulpropertyforsecurityapplications
7、inwhichitisimportantthatmaterialscanbeidentifiedprecisely.Moreover,whenthefilmiswarped,thespacesbetweenthecrystalschange—andthecoloursproducedchangewiththem.Thesetwopropertiesmakeopalescentfilmanobviousmaterialforcurrency.Banknotescontainingitwouldproducedistinctivecoloursw
8、henstretched,unlikecounterfeitsmadefromothermaterials.Tousethefilmtodetectfoodspoi
