A cellulose liquid crystal motor: a steam engine of the second kind.

0.52 MB·English

by  Geng, Yong

A cellulose liquid crystal motor: a steam
engine of the second kind
SUBJECTAREAS:
YongGeng1,PedroLu´cioAlmeida1,2,SuseteNogueiraFernandes1,ChengCheng3,PeterPalffy-Muhoray3
STRUCTUREOFSOLIDS
&MariaHelenaGodinho1
ANDLIQUIDS
SOFTMATERIALS
LIQUIDCRYSTALS 1CENIMAT/I3N,DepartamentodeCieˆnciadosMateriais,FaculdadedeCieˆnciaseTecnologia,UniversidadeNovadeLisboa,
2829-516Caparica,Portugal,2A´reaDepartamentaldeF´ısica,InstitutoSuperiordeEngenhariadeLisboa,InstitutoPolite´cnicode
SURFACES,INTERFACESAND Lisboa,R.ConselheiroEm´ıdioNavarro,1,1950-062Lisboa,Portugal,3LiquidCrystalInstitute,KentStateUniversity,Kent,Ohio
THINFILMS
44242,USA.
Received
Thesalientfeatureofliquidcrystalelastomersandnetworksisstrongcouplingbetweenorientationalorder
24October2012 andmechanicalstrain.Orientationalordercanbechangedbyawidevarietyofstimuli,includingthe
presenceofmoisture.Changesintheorientationofconstituentsgiverisetostressesandstrains,whichresult
Accepted
inchangesinsampleshape.Wehaveutilizedthiseffecttobuildsoftcellulose-basedmotordrivenby
3December2012
humidity.Themotorconsistsofacircularloopofcellulosefilm,whichpassesovertwowheels.Whenhumid
Published airispresentnearoneofthewheelsononesideofthefilm,withdrierairelsewhere,rotationofthewheels
4January2013 results.Asthewheelsrotate,thehumidfilmdries.Themotorrunssolongasthedifferenceinhumidityis
maintained.Ourcelluloseliquidcrystalmotorthusextractsmechanicalworkfromadifferenceinhumidity.
Correspondenceand
Celluloseisthemostcommonorganiccompoundonearth.Itisthestructuralcomponentofthecellwallsof
requestsformaterials
green plants, constituting about a third of all plant matter. It is a polysaccharide, the linear polymer
shouldbeaddressedto (C H O ) ,where102vnv104.Becauseofitsubiquityandimportance,considerableattentionhasbeen
6 10 5 n
P.P.M.(mpalffy@cpip. giventoitsstudyandcharacterization1.Inadditiontopaperproducts,itisusedtoproducecellophane,rayonand
kent.edu)orM.H.G. gunpowder,andwellasadhesives,thickenersandstabilizers.Itisalsoanadditivetopreventcakingofparmesan
([email protected]) cheesepowders.
Hydroxypropylcellulose (HPC) is a commercially available derivative of cellulose in which some of the
hydroxyl groups in the repeating glucose units have been hydroxypropylated. The structure is shown in
Fig. 1a. Due to the presence of both hydrophobic and hydrophilic groups, it has a lower critical solution
temperaturethancellulose;below45uC,itiswater-soluble.Itisbiodegradable,biocompatibleandelectroneutral,
wellsuitedforpharmaceuticalandfoodapplicationsasthickeners,emulsifiersandencapsulators2.Itisalsoused
inartificialtears.
AqueousHPCsolutionsareisotropicatlowpolymerconcentrations,typicallyconsistingofseparatepolymer
chainsinthesolvent.Athigherconcentrations,thehydrophobichydroxypropylgroupspromotetheassociation
ofpolymerchainstoformrigidrod-likefragments3.Thechainsinthefragmentsaremaderigidbyintramolecular
hydrogenbondingofthesidechainhydroxylpropylgroups,andareheldtogetherbyintermolecularhydrogen
bonds and London dispersion forces. The molecules are packed into crystallites ,470 A˚ long and ,34 A˚
diameter4. These micro-fibrils, in turn, associate to form supermolecular rod-like fragments, resulting in a
networkofrigidrod-likefragmentsjoinedtogetherbyflexiblepolymerlinkages.Asthepolymerconcentration
isincreased,theincreasinglydenselypackedrodlikefragmentsbecomeparallel,andliquidcrystalmesophasesare
formed5.
Liquidcrystals(LCs)areliquidswithorientationallyorderedconstituents.Theirbrokencontinuoussymmetry
givesrisetolowenergyexcitations-Goldstonemodes.Consequently,LCsareexceptionallyresponsivetoexternal
stimuli, enabling LCD technology as well as other novel applications6. Simple nematic orientational order is
(cid:4) (cid:5)
characterizedbyatensororderparameterQ ~ 1(cid:2)3l l {d (cid:3) ,wherel isacomponentofaunitvector^l
ab ab ab a
2
alongthesymmetryaxisofamesogenicmoleculeorparticle;thebracketsdenoteensembleaverage.Physical
properties, such as the density, dielectric permittivity and magnetic permeability, are functions of Q . In a
ab
uniaxial system, the order parameter may be written as Q ~S1(cid:2)n n {d (cid:3), where {1ƒSƒ1 is a scalar
ab a b ab
2 2
orderparameter,andn^isthenematicdirector,aunitvectoralongthedirectionofaveragealignment.
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Figure2|Stress-strainrelations. Squarescorrespondtostrainparallelto
thesheardirectionandthenematicdirector.Circlescorrespondtostrain
perpendiculartothesheardirectionandthenematicdirector.Forthis
geometry,aboveathreshold,thestressisnearlyindependentofstrain.This
indicates‘semi-soft’elasticity,characteristicofnematicelastomers.The
Figure1|Molecularstructureandthinfilmpreparation. (a)Idealized negativeslopeathigherstrainscorrespondstofailureduetotearingofthe
chemicalstructureofhydroxypropylcellulose(HPC),R- films.
CH CH(OR’)CH or-H(R9-Hor-CH CH(OH)CH ),withanaverage
2 3 2 3
degreeofsubstitutionof3.5.(b)Schematicofapparatususedtoproduce Results
HPCshearcastfilmsfromlyotropicliquidcrystallinesolutions,with AnisotropicHPCfilmsareformedbytheevaporationofwaterfrom
differentthicknesses(range30–100mm)dependingontheGardnerknife liquidcrystalline aqueous HPCsolutions (60%w/w). In preparing
gapandvelocity.(c)3Dtopographicimage(23323mm2scan)ofthefree samples,solutionsareinitiallyonaglasssubstrate,withafreesurface
surfaceofashearedHPCfilm. exposedtoair.Whenthecelluloseconcentrationissufficientlyhigh
for the formation of the liquid crystal phase, the mesogenic frag-
Elastomers are rubber-like solids characterized by an elastic ments can be uniformly aligned in the sample by shear. Shear is
modulus on the order of MPa which can accommodate strains appliedviaacalibratedGardnerknifemovingatacontrolledspeed
.100%. In 1975, P.G. de Gennes proposed the concept of liquid of1.25 mms21onthefreesurface,asshowninFig.1b.;theprocess
crystal elastomers (LCEs), cross-linked polymer networks with
produces a monodomain nematic sample. As indicated by X-ray
orientationally ordered mesogenic units7. LCE materials weresyn- studies19,thedirectoralignsalongthesheardirection.Asevaporation
thesizedandsamplesproducedforthefirsttimebyH.Finkelmann8.
continues,thedensityofrod-likefragmentsincreasesnearthefree
Thekeyaspectofthesenew‘solid’liquidcrystalsiscouplingbetween
topsurface,givingrisetoincreasedorientationalorder.Thisinturn
mechanicalstrain,e andorientationalorder,Q .Duetothesym-
ab ab causeselongationatthetopofthefilminthedirectionparalleltothe
metry allowed scalar Q e which appears in the free energy, an
ab ba director,andsincethedimensionsofthebottomsurfaceincontact
appliedstrainwillchangeorientationalorder,similarlytoanapplied
withtheglasssubstratearefixed,thetopsurfacebuckles,forminga
electricfield,andallphysicalpropertieswhichdependonit.More
set of grooves20. This can also be seen in Fig. 1c. The final film
importantlyfortheworkreportedhere,anychangeinorientational
thickness is ,40 mm microns. The grooves, whose wave vector is
orderwillresultinmechanicalstrain,similartothatresultingfrom
alongthesheardirection,are,3 mmapart,withamplitude,45 nm.
externalstress,causingachangeintheshapeoftheelastomersample.
Thestructureofthefilmneartheglasssurfaceislesswellunderstood.
Due to their unusual behavior, LCEs have received considerable
Here,thesolventremainsduringshear,solessalignmentisexpected.
attention,theirsalientfeaturesarediscussedindetailinRefs.9,10.
Thefilms,removedfromthesubstrate,arelargearea,free-standing
Changes in the order parameter caused by heating, illumination,
flexiblemacroscopicsamples.
exposuretoelectricfieldsorthepresenceofchemicalsolventsgive
Themodulusofthecellulosenetworkhasbeenmeasuredforstrain
risetocorrespondingchangesinsampleshape11–14.Themesogenic
alongthedirector,aswellasperpendiculartoit.Resultsareshown
unitsmaybeincorporatedintothepolymermainchain,ortheycan
in Fig. 2; for small strains, Young’s modulus is 263+39MPa
be attached via side-chains. In main chain LCEs, the increase of
nematicorderleadstoanincreaseinsamplelengthalongthedir-
ector, and a contraction in the two perpendicular directions. A
decreaseinorderhastheconverseeffect.
Polymernetworksarestructurallysimilartoelastomers,butdueto
highercross-linkdensity,theirmodulusisintheGParange.Liquid
crystal networks (LCNs) show similar behavior to LCEs in their
responsetoexcitations,excepttheyaremuchstiffer.Althoughtyp-
icallytheorientationallyorderedconstituentsofLCsaremolecules,
theymayalsobeelectronstates15,ornano-16ormicro-17particles.In
the case of HPC, the orientationally ordered constituents are the
mesogenic rigid fragments18. HPC films behave, as LCNs; their Figure3|Bendingoffreestandingfilms.(a)Thefilmfreetopsurfaceand
remarkable response to stimuli, discussed below, is the result of (b)thefilmglassbottomsurfaceexposedtowatervapor.Shearedfilms
liquid crystallinity of the rod-like fragments, and the coupling of werepreparedfromliquidcrystallineHPC/watersolution,thearrows
orientationalordertomechanicalstrain. indicatesheardirection.
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exposingtheglasssidetowatervaporisconsiderablysmallerthan
thatofthefreesurface.
WatervaporinducedbendhasbeendemonstratedinDNAcov-
ered Si cantilevers21, as well as in a different LCN system with a
differentgeometrybyBroeretal.14.Inthiswork,wehaveexploited
suchabending phenomenonto produceahumidity drivenrotary
motor.
Thereexistawidevarietyofdefinitionsofmotorsintheliterature.
Wechooseheretodefineamotorasadevice,whichusesenergy,but
not momentum, to produce motion. Engines may be defined as
motors,whichobtainenergyfromafuel.
Our humidity driven motor is shown below. A monodomain
nematic HPC film was produced in the form of a circular loop,
8.0cmlong,and1.0cmwide(Fig.5).Thealignmentdirectionisin
theplaneofthefilm,perpendiculartothelongedges.Theloopwas
passedovertwo14mmdiameterwheelswithhorizontalaxes.When
humid airwas applied to the outer side ofthefilm nearoneof the
Figure4|Dynamicsofstressevolution. Shearstressina20mm3
wheels,asshowninFig.5,thewheelsbegantorotate,andcontinued
20mm332mmplanarsampleat24uCwithfreesurfaceexposedto solongashumidairwaspresent.Themotioniscausedbyhumidity-
humidityasfunctionoftime,measuredwithaMettlerToledoAG204load
inducedbendoftheliquidcrystallineHPCfilm.Aheuristicexplana-
sensor.Themaximumstressmeasuredwas383Pa.
tionforthemotionisasfollows.Ifthetensioninthefilmisassumed
tobenearlyuniform,thehumidityinducedbendshortensthelever
for shear parallel and 140+9MPa perpendicular to the director. arm on the side where the moist air is applied, resulting on a net
Aboveathresholdof4MPa,thestressintheperpendiculardirection torqueonthewheelandcausingrotationofthewheelasillustrated
isnearlyindependentofthestrain.This‘semi-soft’elasticresponseis schematicallyinFig.6.Wehaveestimatedthetensilestressfromthe
characteristicofliquidcrystalelastomers9.Whenexposedtowater shapeofthecircularfilmlooptobe357Pa,whichisclosetotheshear
vapor,freestandingfilmspreparedfroma60%w/wsolutionbend,as stressproducedbyhumidity.Weconjecturethatthesetwoquantities
showninFig.3.Whenwatervaporpenetratesthefreesurfaceofthe needtobecomparablefortheenginetooperateefficiently.
film,thesamplebendsaroundanaxisparalleltothesheardirection, Asthemotorrotates,thehumidfilmdries.Keytotheprocessisthe
withthefreesurfaceontheoutside(Fig.3a.).Thisisconsistentwith spontaneouscurvatureofthefilmintheregionnearthewheelwhere
expansionofthefreesurfaceofthefilminthedirectionperpendic- thehumidityisapplied.Themotorcanbemadetorotatefasterifthe
ulartothedirector.Suchanexpansionisexpected,sincetheorder ambient temperature is increased, or, equivalently, if the ambient
parameterisreducedbythepresenceofthesolventwater,andfur- humidityisreduced.Adetailedmodelwillbepublishedelsewhere.
thermore the presence of water molecules between the cellulose
chains in the rigid segments is expected to cause the thickness of Discussion
therod-likefragmentstoincrease. The energy to drive the motor comes from water vapor – from
Theshearstressassociatedwithsuchbendhasbeenmeasured,asa ‘‘steam’’.Inconventionalsteamengines,fuelisburnedtoheatthe
function of time (Fig. 4), in a 20 mm 3 20 mm 3 32 mm planar water, raising the chemical potential of the water vapor due to
sampleat24uCwithfreesurfaceexposedtohumidity.Measurements increaseinthetemperature.Freeenergyisconvertedintoworkby
weretakenwithMettlerToledoAG204loadsensor.Themaximum the engine. Our steam engine exploits the difference in chemical
stressmeasuredwas383 Pa. potentialofwatermoleculesinhumidandindryair;theLCNbelt
When the film is allowed to dry, either by heating or by being transportsthewaterfromregionsofhighchemicalpotentialtolow,
placedinalow-humidityenvironment,thefilmunbends,reversibly gainingenergyintheprocess.Thedifferenceinchemicalpotentialm
assumingitsoriginalshape.Thebendingisrelativelyfast,onthescale isgivenby22
of,1 s. (cid:6)x (cid:7)
Interestingly,whentheglasssideofthefilmisexposedtowater m2{m1~kTln x2 ð1Þ
vapor,itbendsaroundanaxisperpendiculartothesheardirection, 1
withtheglasssidebeingconvex(Fig.3b.).Thisisconsistentwitha wherekisBoltzmann’sconstant,Tistheabsolutetemperature,andx
nearlyisotropicexpansionoftheglasssidesurfaceduetothepres- istherelativehumidity.Iftherelativehumiditiesare30%and70%,as
enceofmoisture.Sincecorrugationsonthefreesurfacegiverisetoa inourexperiments,theamountofenergyavailableforworkatroom
smaller effective modulus for bend in this direction, as has been temperatureis2.1 KJ/moleofwater,orapproximately100 J/g.The
confirmed by independent measurements, bend occurs around an underlying mechanism is similar to that of the collagen engine of
axis perpendicular to the shear direction. The bend produced by Katchalsky23,whichisdrivenbythechemicalpotentialdifferenceof
Figure5|Moisture-drivenliquidcrystalcelluloseengine. (a)Schematicofthemotor,showinglocationofmoistairandrotationdirection.The
alignmentdirectionisparalleltotheaxesofthewheels.Thefreesurfaceofthefilmisontheouterside.(b)Seriesofvideoframesshowingrotation.(Movie
ofthemotorisavailableundersupplementarymaterials.)Themotorishousedinadryenvironment.Momentumtransferfromthemoistairissmall,and
opposestheobservedmotion.Beltdimensionsare:1.0cm38.0cm330mm;wheeldia.is14mm.Thedirectionofrotationisindicatedbyablackarrow,
andofmoistairflowbyawhitearrow(a).In(b),t52s/frame.
SCIENTIFICREPORTS |3:1028|DOI:10.1038/srep01028 3
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1. Jarvis,M.Chemistry:cellulosestacksup.Nature426,611–612(2003).
2. Kondo,T.inPolysaccharides(edS.Dumitriu)(MarcelDekker,NewYork,2005).
3. Evmenenko,G.,Yu,C.J.,Kewalramani,S.&Dutta,P.Structuralreorganizationin
filmsofcellulosederivativesinthepresenceofcolloidalparticles.Polymer45,
6269–6273(2004).
4. Samuels,R.J.Solid-StateCharacterizationofStructureandDeformationBehavior
ofWater-SolubleHydroxypropylcellulose.JPolymSciA27,1197–&(1969).
5. Patra,A.,Verma,P.K.&Mitra,R.K.Slowrelaxationdynamicsofwaterin
hydroxypropylcellulose-watermixturetracesitsphasetransitionpathway:a
spectroscopicinvestigation.Thejournalofphysicalchemistry.B116,1508–1516
(2012).
6. Palffy-Muhoray,P.Thediverseworldofliquidcrystals.PhysicsToday60,54–57
(2007).
7. Gennes,P.G.d.,Chung,T.C.&Petchsux,A.Re´flexionssuruntypedepolyme`res
ne´matiques.C.R.Acad.Sci.Ser.B281,101–103(1975).
8. Finkelmann,H.,Kock,H.&Rehage,G.InvestigationsonLCpolysiloxanes:3.
Figure6|Schematicofthehumidityinducedbendingmechanism. Liquidcrystallineelastomers-anewtypeofliquidcrystallinematerial.
(a)Theconfigurationissymmetricaboutaverticalaxis.Theleverarms MakromolekulareChemie,RapidCommunications2,317–322(1981).
(green)areofequallength,andthenettorqueonthetopwheeldueto 9. Warner,M.&Terentjev,E.M.Liquidcrystalelastomers.(OxfordUniversityPress,
Oxford,2007).
tensioninthefilmiszero.(b)Duetothehumidity-inducedbend,the
10.Liquidcrystalelastomers:materialsandapplications.(Springer,NewYork,2012).
configurationisnolongersymmetric.Leverarmontherightintopwheel 11.Kupfer,J.&Finkelmann,H.Liquid-CrystalElastomers-Influenceofthe
isshorter;nettorqueontopwheelduetotensioninthefilmgivesriseto OrientationalDistributionoftheCross-LinksonthePhase-Behaviorand
CWrotation.(Thehumidityinducedbendhasbeenexaggeratedtoaidthe ReorientationProcesses.MacromolChemPhysic195,1353–1367(1994).
illustration.) 12.Yu,Y.L.,Nakano,M.&Ikeda,T.Directedbendingofapolymerfilmbylight-
Miniaturizingasimplephotomechanicalsystemcouldexpanditsrangeof
applications.Nature425,145–145(2003).
NaClinsalinesolutionsandpurewater.Whereashiscollagenfibers 13.Urayama,K.,Honda,S.&Takigawa,T.Electroopticaleffectswithanisotropic
contractedinthepresenceofsalt,ourLCNbendsinthepresenceof deformationinnematicgels.Macromolecules38,3574–3576(2005).
humidity.Sinceoursteamenginerunsisothermally,itdiffersfun- 14.Harris,K.D.,Bastiaansen,C.W.M.&Broer,D.J.Aglassybending-mode
polymericactuatorwhichdeformsinresponsetosolventpolarity.Macromol
damentallyfromconventionalsteamenginesinthatitisnotaheat
RapidComm27,1323–1329(2006).
engine.Wecallitthereforeasteamengineofthesecondkind,and 15.Tanatar,M.A.,Paglione,J.,Petrovic,C.&Taillefer,L.Anisotropicviolationofthe
notethat,consequently,itsefficiencynotlimitedbythatofCarnot Wiedemann-Franzlawataquantumcriticalpoint.Science316,1320–1322
cycles.Itappears,fromEq.(1),thatconsiderableenergyisavailable (2007).
16.Shopsowitz,K.E.,Qi,H.,Hamad,W.Y.&Maclachlan,M.J.Free-standing
forworkfromreservoirsofhighandlowhumidity;ourenginepro-
mesoporoussilicafilmswithtunablechiralnematicstructures.Nature468,
videsanewmethodofobtainingworkfromahumiditydifference.
422–425(2010).
In summary, we have demonstrated a new type of soft motor, 17.Tkalec,U.,Ravnik,M.,Copar,S.,Zumer,S.&Musevic,I.Reconfigurableknots
usingacelluloseliquidcrystalfilm,drivenbyadifferenceinhumid- andlinksinchiralnematiccolloids.Science333,62–65(2011).
ity.Themotorissimple;itreliesonthemoisture-inducedbendofthe 18.Werbowyj,R.S.&Gray,D.G.Optical-Propertiesof(Hydroxypropyl)Cellulose
Liquid-Crystals-CholestericPitchandPolymerConcentration.Macromolecules
HPC,whicharisesfromthecouplingbetweentheorientationorder
17,1512–1520(1984).
oftherigidrod-likefragmentsofthenetworkandmechanicalstrain.
19.Godinho,M.H.etal.Liquidcrystallinecellulosederivativeelastomerfilmsunder
Changesinorientationalorderarecausedbytheabsorptionofwater uniaxialstrain.Cellulose16,199–205(2009).
molecules. As the engine rotates, the moist film dries in a dry air 20.Godinho,M.H.,Fonseca,J.G.,Ribeiro,A.C.,Melo,L.V.&Brogueira,P.Atomic
environment, and returns to its original shape, ready to perform forcemicroscopystudyofhydroxypropylcellulosefilmspreparedfromliquid
crystallineaqueoussolutions.Macromolecules35,5932–5936(2002).
work again when exposed to moist humidity. Since the transport
21.Mertens,J.etal.Label-freedetectionofDNAhybridizationbasedonhydration-
of water is via directed diffusion along concentration gradients, it inducedtensioninnucleicacidfilms.NatNanotechnol3,301–307(2008).
isexpectedthatsmallermotorswillrunfaster.Micromotorsoper- 22.Abraham,N.&Palffy-Muhoray,P.Adunkingbirdofthesecondkind.AmJPhys
atingonthisprinciple,usingthechemicalpotentialofliquidwateror 72,782–785(2004).
moistairmaybeusefulinreducinghumidityorproducingmech- 23.Steinberg,I.Z.,Oplatka,A.&Katchalsky,A.MechanochemicalEngines.Nature
210,568–571(1966).
anicalorelectricalenergy.Furtherstudiesareneededtodetermine
theefficiencyoftheenergyconversionprocessinsuchasteamengine
ofthesecondkind.
Acknowledgements
Methods WeacknowledgesupportfromthePortugueseScienceandTechnologyFoundation
(5aHs1ry0edc0re.o0ivx0ey0dp.grS/omoplyoullt);icomenlolsuloalorfsHseuPb(HCstPiitnCudt)iiowsntai,lslMepdSuwr5caht3ea.rs5ew,daistfhrdocemotenrScmeignimntreaad-tAiboylnd1roHifc6Nh0M(%MR(Ww)a/nwd)wuseerde tFPheErrsontu-aCgnh/dCegsTrarMnest/psLeAScF0tiR0v2He5l/y/B,2Dp01r/o16j3e(5cS7ttsr4aP/t2eT0gD0ic9C,P/SCrFoTRjeMHct//0B-9PL9DA5/927558/24-0320008/12,10P–1T12D0t1oC2/Y)F.aIGSn/de1n1fgr0o1am3n2dt/h2Se0.N0U9..,S.
preparedatroomtemperature.Afterthefirstweektheywerestirredeveryotherday NationalScienceFoundationIIP1114332.
andkept,awayfromlight,foratleast4weeks,untilused.
FilmswerepreparedfromLCsolutions,castedandshearedsimultaneouslyby Authorcontributions
movingacalibratedGardnerknifefromBraiveInstrumentsat1.25mms21.Thefilms
Y.G.,P.L.A.andS.N.preparedsamplesandworkedondevelopingthemotor.C.C.worked
wereallowedtodryatroomtemperatureandwerekeptina(20%)controlled
onoptimizingthemotor.P.P.-M.andM.H.G.conceivedofanddirectedtheprojectand
humiditychamberuntilused.Thethicknessofthedriedfilmswasestimatedby
wrotethispaper;theycontributedequallytothiswork.
averaging10measurementswithaMitutoyodigitalmicrometer.
Toconstructthemotor,thecellulosicfilmwasproducedintheformofacircular
loop,8.0cmlong,1.0cmwide,whichpassesovertwo14mmdiameterwheels. Additionalinformation
ThewatervaporwasgeneratedbyanAirProjectultrasonichumidifier(Italy Competingfinancialinterests:Theauthorsdeclarenocompetingfinancialinterests.
ARTSANAGroup).
License:ThisworkislicensedunderaCreativeCommons
PhotographsandmovieofthecellulosicfilmandmotorweretakenwithaCasio
Attribution-NonCommercial-NoDerivs3.0UnportedLicense.Toviewacopyofthis
EX-F1ExilimProandCanonEOS550Dphotocamera.Blender,version2.57b,was
license,visithttp://creativecommons.org/licenses/by-nc-nd/3.0/
usedtoobtainthe3Ddrawoftheshear-castingknifeandmotor.
Howtocitethisarticle:Geng,Y.etal.Acelluloseliquidcrystalmotor:asteamengineofthe
secondkind.Sci.Rep.3,1028;DOI:10.1038/srep01028(2013).
SCIENTIFICREPORTS |3:1028|DOI:10.1038/srep01028 4