Receive Jun 0 Accepte Nov 0 Pulishe 6 Dec 0DOI: 0.038/ncomms583 Grphene chirl liqui crystls n mcroscopic ssemle fires Z h e n Xu & Ch o G o Chirlity n liqui crystls re oth wiely expresse in nture n iology. Helicl ssemly of mesophsic molecules n collois my prouce intriguing chirl liqui crystls. To te, chirl liqui crystls of D collois hve not een explore. As typicl D colloi, grphene is now receiving unpreceente ttention. However, mking mcroscopic grphene fires is hinere y the poor ispersiility of grphene n y the lck of n ssemly metho. Here we report tht solule, chemiclly oxiize grphene or grphene oxie sheets cn form chirl liqui crystls in twist-grin-ounry phse-like moel with simultneous lmellr orering n long-rnge helicl frustrtions. Aqueous grphene oxie liqui crystls were continuously spun into metres of mcroscopic grphene oxie fires; susequent chemicl reuction gve the first mcroscopic net grphene fires with high conuctivity n goo mechnicl performnce. The flexile, strong grphene fires were knitte into esigne ptterns n into irectionlly conuctive textiles. MOE Key Lortory of Mcromoleculr Synthesis n Functionliztion, Deprtment of Polymer Science n Engineering, Zhejing University, 38 Zhe Ro, Hngzhou 3007, PR Chin. Corresponence n requests for mterils shoul e resse to C.G. (emil: chogo@zju.eu.cn ).
L iqui crystlline collois re of gret interest ue to their significnce in unerstning colloi physics n ccessing flui-phse ssemly. The chirl liqui crystls (CLCs) of oneimensionl (D) collois such s DNA, cteriophge f virus n imogolite 3 hve een reporte. Vrious conventionl liqui crystlline mesophses of two-imensionl (D) collois nemtic, columnr n lmellr hve een reporte 4 0. However, the CLC phse of D collois hs not een reporte previously, possily ecuse no one knows whether chirl flke prticles cn form long-rnge helicl systems. As typicl D colloi, grphene, single tomic lyer of grphite, consists of sp -hyriize cron toms in honeycom lttice. It hs possily ecome the fstest growing topic in science n technology ecuse of its mrvellous properties such s the strongest mechnicl strength ever mesure, gint intrinsic crrier moility, tunle n gp or electricl conuctivity n recor therml conuctivity 5. Avnces hve een chieve in the re of grphene-se evices n composites 5 9, ut to effectively trnslte the properties of grphene into mcroscopic-orere mterils, such s continuous fires, chllenges must e overcome in terms of its limite ispersiility in common solvents s the lck of sclle ssemly methos 0. Alterntively, chemiclly oxiize grphene or grphene oxie (GO), the most ccessile precursor of grphene, possesses goo soluility in wter n polr orgnic solvents, n cn form lyotropic nemtic liqui crystls (LC),, typicl mesophse of highly nisotropic collois 4,3. This conventionl phse ehviour of GO sheets coul le to the iscovery of novel mesophses. Furthermore, GO LC with regulr orering promises the most vile flui ssemly pproch to mcroscopic grphene fires vi wet-spinning techniques. Such fires woul further result in roust n conuctive textiles useful for numerous pplictions, in the light of strong Kevlr fires n cron nnotue (CNT) fires 4 6 similrly spun from their liqui crystlline spinning opes. Here we iscover n emonstrte tht GO sheets cn form CLC in their queous ispersions tht oeys twist-grin-ounry (TGB) phse-like moel. The first continuous, net grphene fires, without ny supporting surfctnt or polymer, hve een prouce y inustrilly vile wet-spinning of GO LCs followe y chemicl NATURE COMMUNICATIONS DOI: 0.038/ncomms583 reuction. The grphene fire possesses goo mechnicl performnce ( ~ 40 MP t ultimte elongtion of 5.8 % ) n high conuctivity ( ~.5 0 4 S m ). The fires cn e woven into esigne ptterns n complex textiles. This LC-se wet-spinning technology promises rn-new methoology to fricte high-performnce cronceous fires with verstile functionlities from nturl grphite. Results Textures of GO CLCs. The GO sheets we use re single-lyere, nrrowly polyisperse n iniviully isperse in wter ( Fig., ; Supplementry Fig. S ). The D morphology n with istriution of GO sheets re emonstrte in Figure,, respectively. Their verge thickness ( t ) is 0.8 nm n the verge lterl with ( w ) is 0.8 μ m with nrrow polyispersity of 3 % (much lower thn 83 % of the crue GO smple without size frctiontion ). The GO queous ispersions were oserve y polrize opticl microscopy (POM) etween crosse polrizers ( Fig. c h ). Upon incresing the volume frction ( φ ) to 0.3 %, GO ispersions evolve from lnk to Schlieren texture ( Fig. c ), typicl irefringent texture of nemtic LCs 7,8, 3. Accoring to the moel for polyisperse infinitely thin pltelets, this concentrtion of isotropic nemtic phse trnsition (0.3 % ) is very close to the theoreticl vlue (0.5 % ) 3. In the stle nemtic phse, the lck rushes represent the isclintions of orienttionl orers, corresponing to the neighouring crosse irect vectors ( Fig. ). As φ increses up to 0.39, 0.60 n 0.76 %, the textures turn into ligne, vivi ns, which re similr to the fingerprint texture of cholesteric phse 7 n Grnjen texture of TGB phse 8 (Fig. e g, itionl fingerprint textures see Supplementry Fig. S ). As the incomptiility of helicl irector fiel n smectic-lyere feture in continuous system results in frustrte structures contining regulr screw lttice of grin ounries in TGB phse 8, we cn speculte tht the textures of our smples result from the helicl rrngement of GO sheets with vectors mp etween neighouring ns s inicte in Figure h. The with of these ligne ns coul e relte to the pitch length, n ecomes thinner with φ incresing from 0.39 % ( Fig. e ) to 0.60 % ( Fig. f ) n 0.76 % ( Fig. g ). Such ligne ne structures hve een confirme y c 0.8 nm P (w) 0.04 0.0 0.5.0.5 w (μm) e f g h Figure Atomic force microscopy imge of grphene oxie sheets n POM oservtions of GO queous ispersions. ( ) Typicl tomic force microscopy imge of GO sheets. ( ) The with istriution of GO sheets otine from Supplementry Figure S. ( c g ) POM imges of GO LCs with successively increse volume frctions ( φ s) of 0.3, 0.38, 0.60, 0.76 %. (,h ) Director fiels of the isclintion in the nemtic phse (rectngle in c ) n the fingerprint texture of chirl phse ( e g ). The irector vector ( n ) is efine s the norml irection of GO sheet plne. The crosses inicte n s into the pper n the rrows show n s on the pper in n h. Scle rs, μm ( ) n 00 μm (c,e g ).
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 ARTICLE c I q 50 00 50 00 50 Δ 00 (nm) 00 80 60 40 0 50 00 50 00 50 / 4 3 e 00 (nm) 60 50 40 30 0.0 0. 0. 0.3 0.4 0.5 0.6 0.7 q (nm ) E-6 E-5 E-4 E-3 E- Slt concentrtion (M) Figure SAXS investigtion of GO queous ispersions. ( c ) D scttering ptterns of GO ispersions with successive volume frctions ( φ s) of 0.38, 0.9 n.5 %. The iffusive rcs (rrows) in n c enote the reflection rcs. ( ) Profiles of scttering intensity s function of scttering vector q (q = 4 π sin θ /λ = π / ) in smples with successive φ s of 0.38,.06,.5 n. % (successively numere y 4). The tringulr, imon n hert signls enote the first-, the secon- n the thir-orer scttering peks in orer. Inset: the correltion of (00) spcing n / φ ; the re ots re experimentl vlues n the lue line is the fitting function in the liner region ( φ 0.5 % ). (e ) Vrition of the interlyer spcing with slt concentrtion t φ =.0 %. lser confocl microscopy with the fluorescent chrcter of GO sheets (Supplementry Fig. S3 ). Lmellr structure in GO CLCs. Smll-ngle X-ry scttering (SAXS) stuies further revele quntittive structurl informtion of GO ispersions ( Fig. ; Supplementry Fig. S4 ). In the very ilute isotropic ispersion ( φ 0.03 % ), the X-ry scttering intensity ( I ) monotonously ecreses with scttering vector moulus ( q ) s I ~q, following the typicl scttering lw of D plnr collois n proving the flt morphology of isperse GO sheets 8,9. In the nemtic GO phse ( φ 0.3 % ), ellipticl SAXS iffusive pttern together with the sence of shrp scttering pek inictes the sole orienttionl orer in the ilute ispersions ( Fig. ). In comprison, for those concentrte ispersions ( φ 0.38 % ) with ligne ne textures ( Fig. e g ), strong nisotropic ptterns ( Fig. c ) n multiple correltion peks (up to 3) re oserve ( Fig. ). The profiles of scttering intensity s function of scttering vector show etile informtion of lmellr orers epening on GO concentrtion, n the peks cn e inexe to the 00 reflection of the lmellr structure 8,9. Compre with the wiely isperse GO LCs, the nrrowly isperse GO LCs show stronger reflection signls, emonstrting more orerly orgnize structures resulte from their more uniform istriution in size. Prticulrly, the evolution of interlyer spcing ( = π /q 0 ) upon the inverse volume frction ( / φ ) is conclue in Figure insert (etile t see Supplementry Tle S ). At 0.5 % < φ <.3 %, the evolution isplys liner reltion, where is proportionl to /φ ( = t / φ, t is the thickness of D collois), following the typicl D swelling ehviour of lmellr D collois LCs 8,9. The fitting line slope reflecting the experimentl thickness of GO sheets is 0.46 ± 0.03 nm, ner to the theoreticl thickness of monolyer grphene sheet (0.34 nm), which proves tht GO sheets re perfectly exfolite to iniviul ones in their LCs. The liner region ens s φ pproches 0.5 %, roun the trnsition concentrtion ( φ 0.38 % ) from nemtic to lmellr phse oserve in POM investigtions ( Fig. c,e ). For ilute ispersions with lower φs, vlue is evite from the first liner region, possily suggesting the isotropic volume swelling ehviour in the nemtic phse. Similr to the liqui crystlline system of phosphtontimonte pltelets 9, the mjor interction minly consiere to stilize the GO LC in n queous surrouning is the electrosttic repulsion ecuse of the negtive zet potentil ( 6 ± 5 mv) of GO sheets n the strong slt effect of its LC phse. We performe SAXS mesurements for the smples with grient slt concentrtions t the sme GO volume frction ( Supplementry Fig. S5 ). The interlyer spcing clculte from the corresponing SAXS ptterns lrgely ecreses t reltively high ionic strength eyon [NCl] 0 4 M ( Fig. e ), ecuse the electrosttic interctions re strongly screene 9. As result, t φ = 0.7 %, the interlyer spcing flls from 63 nm in pure wter to 4 nm t [NCl] 0 M. As the slt concentrtion rises to 0. M, flocculte solis re emerge, n the corresponing SAXS pttern shows neither scttering peks nor nisotropy, implying tht the flocculte solis consist of rnomly ggregte GO sheets. CD ctivity of GO CLCs. For CLC, circulr ichroism (CD) is useful tool to chrcterize the selective reflection coefficients for right- n left-hne circulrly polrize wves 9,30. To exmine the chirlity of our GO CLCs, we otine their CD spectr, s shown in Figure 3. The CD ctivity is very wek for the ilute GO ispersions, n ecomes stronger upon incresing φ, for instnce to 0.38 % ( vlue close to nemtic CLC phse trnsition). Very strong CD signl (up to,400 milliegree) is etecte s φ rises to 0.76 % ( vlue of GO CLC with stle lmellr structure). The 3
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 Ellipticity (egree) Ellipticity (normlize) 0.0 0.8 0.6 0.4 0. 0.0 0.78 % 0.38 % 0.075 % Film 300 400 500 600 700 800 Wvelength (nm) 5 4 3 Log ([NCl]) Figure 3 CD ctivity of GO CLCs. ( ) CD spectr of GO queous ispersions n GO soli film. ( ) Normlize CD ctivity of GO CLC ( φ =.0 % ) s function of slt concentrtion. chrcteristic CD spectrum spns roun 40 nm from 380 to 800 nm tht covers wie rnge from ner ultrviolet n visile light to ner infrre, implying grient helicl rrngement of GO sheets. GO CLC with such wie CD response cn e use s potentil opticl components 3. By contrst, no ovious CD ctivity ws etecte for the filtrte trnsprent GO soli films, in which GO sheets re ligne prllel long the film surfce 9. These results vlite tht the CD ctivity of GO CLC is generte y the helicl rrngements of ifferent GO sheets, rther thn y the possile opticl ctivity from the symmetricl structures on GO plnes. Therefore, we cn conclue tht the GO CLC hols oth lmellr n helicl rrngements simultneously. Consiering the mjor role of electrosttic repulsion to ffect the lmellr structure ( Fig. e ), we further ssesse the effect of ionic strength on the CD ctivity of GO CLCs ( Fig. 3 ; Supplementry Fig. S6 ). At low slt concentrtion ([NCl] < 0 4 M), the ellipiticity of GO CLC is strong, n ecys with incresing [NCl] from 0 4 to 5 0 3 M. Eventully, the ellipticity flls to zero t [NCl] > 0 M.. These mesurements clrify tht the helicl rrngement in GO CLCs is ominte y the electrosttic repulsion etween GO sheets. Helicl structures in GO CLCs. The helicl structurl etils of GO CLC hve een irectly visulize y cryo-scnning electron microscopy (SEM), s shown in Figure 4 f. The freeze-frcture morphology of the GO CLC confine to circulr cvity shows nnul ring-like structures comprising of unulting ns with istinct ounries ( Fig. 4 ). We cn istinguish tht GO sheets pile up to form the ns with neighouring orthogonl vectors long the rius, leing to the unulting morphology. The istnce etween two jcent ns cn e ssigne to one-hlf of the pitch ( p /) of the helix ( Fig. 4e ). The mesure pitch ( ~4 μ m) is much wier thn those (0.. μ m) of ever reporte gint TGB phses of smll molecules 3, ue to the lrge lterl with (micrometre scle) of constituent GO sheets. Furthermore, the lmellr feture with regulr interlyer spcing is revele in the sie-view SEM exmintion of the ssemle GO locks ( Fig. 4f ). Menwhile, highly regulr fingerprint-like n focl conic textures ( Fig. 4g i ; Supplementry Fig. S7,c ) re oserve uner POM for the confine GO CLCs in cvity with the sme imeter. These regulr ns re relte to the pitches of CLC helixes ( p ), n the interspcing etween two neighouring ns is 5 5 μ m, close to p / ( ~ μm), scertine from the ove cryo-sem mesurements. The corresponing irector fiel of CLC is epicte in Supplementry Figure S7, in which the vectors ( n s) rotte on the helicl xis (prllel to the surfce) long the rius n form lterntively perpeniculr vector ns. In Figure e g, the texture ns get thinner upon incresing φ, inicting tht the pitch of GO sheets helix nrrows own s the GO concentrtion rises. This les to greter twist etween GO sheet ounries, thus cusing stronger CD ctivity ( Fig. 3 ). TGB-like moel for GO CLC. On the sis of ove experimentl results, we constructe moel in one-pitch rnge for the CLC of D colloil GO sheets tht hols oth continuous lmellr n helicl fetures ( Fig. 5 ). GO sheets ssemle into lmellr locks with locl vector ( n ) in their norml irection, n the etween jcent grphene sheets eceses with the incresing of φ (top left, Fig. 5 ). Becuse of negtive chrges t ounries n on surfces of GO sheets (zet potentil of GO ispersions is 6 ± 5 mv), the neighouring locks repel ech other, forming the rotte conformtion y turning to certin ngle (clculte s 7.0, θ 360w /p t φ = 0.98 % ) to minimize the free energy (ottom right, Fig. 5 ). Along the helicl xis, the locks rotte successively in the sme irection (clockwise or nticlockwise) to estlish the helicl rrngements (centre, Fig. 5 ). In other wors, the negtively chrge grin ounries of GO sheets prouce helicl isloctions in their lmellr fluis n thus set the orerly frustrte structures in their chirl phses. In fct, we cn recognize two twiste neighouring lmellr locks uner the high mgnifiction of cryo-sem ( Fig. 4c ). Our twistlmellr-lock moel for CLCs of D collois cn e nlogous to the reporte TGB phse of conventionl smll molecules 8,33. Chirl silic gels y GO CLC templting. The flui GO CLC cn e fixe y hyrolysis of tetrethyl orthosilicte vi sol gel metho, fforing trnsprent, self-stning gel film ( Fig. 6, ), with the prent structure of GO CLC. The centrl n fringe omins of the film show Schlieren ( Fig. 6c ) n vivi ne textures uner POM ( Fig. 6 ), respectively. The ifference etween textures is likely scrie to the tensile force of the fringe uring cross-linking. Importntly, the film shows consierle CD ctivity, emonstrting tht the gel hols the helicl structure of originl CLC ( Supplementry Fig. S8 ). The resultnt gel films with specific chirlity cn e prcticlly pplie to opticl pprtus 3, n GO CLC coul serve s templtes to fricte chirl porous mterils 34. Continuous grphene fires y wet-spinning. To construct mcroscopic grphene fires is ig chllenge tht remins unsolve. Clerly, wet-spinning is the only vile pproch ecuse of the high-temperture stility of grphene (melt-spinning is not n option), s is the cse for CNTs 4 6. Our iscovery of GO LCs with lmellr structures llows to isperse GO t high-enough concentrtions, suitle for efficient lignment n effective cogultion. For the first time, we hve fricte net GO fires y spinning the queous LCs in cogultion th of 5 wt % NOH / methnol solution (spinning pprtuses re sketche in Supplementry Fig. S9 ). Direct spinning of GO LCs t concentrtions of φ s 0.76 n.0 % resulte in rittle fires n collpse elts, respectively, ( Supplementry Fig. S0 ). From the concentrte LC ispersion (for exmple, φ = 5.7 % ), we otine continuous fires successfully. Metres of GO fires hve een reily prouce in ~ 0 min, with 4
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 ARTICLE c e f p/ g h i Figure 4 Cryo-SEM imges n POM textures for GO CLCs. ( e ) Top-view SEM imges show the frcture morphology of GO CLCs t volume frction φ 0.98 % confine in circulr cvity. The re crosses enote vectors ( n s) into the pper n the ornge rrows on the pper. ( ) The centrl omin in. ( c ) The screw isloction of neighouring GO lmellr locks with twist vectors. ( f ) Sie-view SEM imge of ssemle GO locks. ( g i) POM imges etween crosse polrizers of GO CLCs in centrl ( g ) n lterl ( h,i ) omins. The regulr ring textures ( g i ) re in ccornce with the nnul-ring unulting frcture morphology ( e ) of GO CLC. Scle rs, 00 μm ( ), 5 μm ( f ) n 300 μm (g i ). n Y (00) Z n θ n n Δn n p c X Figure 5 Propose moel for one pitch of GO CLCs. The vectors ( ns) of the lmellr locks rotte nticlockwise long the helicl xis. Top left: the lmellr structure of the orgnize GO lock with n ienticl n n regulr spcing ; the semitrnsprent lue locks inicte interlyer wter, n GO sheets re inicte s pink nets (oule ons in the sl plnes n pent functionl groups hve een omitte for clrity). Bottom right: the screw isloction etween two neighouring grin ounries of GO lmellr locks (the re line enotes GO sheet ounries). The negtive chrges (lue minus) spre the surfce n ounries of GO sheets n mke two locks repulse ech other, with n ngle θ etween two vectors ( n n n ). Figure 6 Chirl gel film templte from GO CLCs. (, ) Respective photogrphs of the chirl gels uner nturl light n etween crosse polrizers. The imeter of the film is 3 cm. ( c, ) The respective POM imges in the centrl zoom n fringe of the chirl film. Scle rs, 00 μ m. 5
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 c e f g h Figure 7 Mcroscopic net GO fires n chemiclly reuce grphene fires. ( ) Four-metre-long GO fire woun on Teflon rum (imeter, cm). SEM imge of the fire ( ), n its typicl tighten knots ( c ). ( ) The frcture morphology of GO fire fter tensile tests. The surfce winkle morophology ( e ) n the tighten knot ( f ) of grphene fire. j: A Chinese chrcter (, Zhong ) pttern knitte in the cotton network (white) using two grphene fires (lck). k: A mt of grphene fires (horizontl) woven together with cotton thres (verticl). Scle rs, 50 μm ( f ) n mm (g, h ). tunle imeters (50 00 μ m), y justing the size of nozzle n the rwing spee ( Fig. 7, ). Typicl knots re me n the fires o not rek s the knots re tightene ( Fig. 7c ; Supplementry Fig. S0 ). The curve structure through 360 emonstrtes the excellent flexiility n high resistnce to torsion of GO fires compre with the clssicl cron fires. Through SEM kept in high mgnitue ( Supplementry Fig. S0c ), we ientifie tht GO sheets ligne in their plnr irections with crumle surfces. Susequently, we prepre net grphene fires y chemicl reuction of GO fires in hyroioic ci (40 % ) 35. The reuce grphene fire shrinks in imeter n exhiits grey metllic lustre. The X-ry iffrction stuies ( Fig. 8 ) inicte tht the interlyer spcing ecreses from 8.9 Å ( θ = 9.86 ) for GO fires to 3.7 Å ( θ = 4.5 ) for grphene fires, vlue close to the interlyer spcing (3.35 Å ) of grphite, ue to the elimintion of pennt functionl groups of GO sheets uring the chemicl reuction. The reuction ws further confirme with Rmn spectr of fires ( Supplementry Fig. S ). The reuce grphene fire shows high electricl conuctivity up to ~.5 0 4 S m, even higher thn the filtrte grphene pper reuce y hyrzine hyrte ( ~ 7. 0 3 S m ) 36. The continuous GO fires exhiit typicl plstic eformtion t room temperture ( Fig. 8 ). This ehviour possily rises from the stretching of the crumle GO sheets n y the isplcements of GO sheets (see the frcture morphology in Fig 7 ; Supplementry Fig. f ). In the elstic region, the fires hve typicl Young s moulus of 5.4 GP t smll eformtion. Importntly, the fires show frcture elongtions of ~6.8 0. %, n orer of mgnitue greter thn tht of filtrte GO ppers ( ~ 0.4 % ) 9. The frcture strength of our GO fires is mesure to e 0 MP, comprle to tht (70 30 MP) of filtrte GO ppers 8,9. The chemiclly reuce grphene fires we otine were strong n flexile. Compre with GO fires, grphene fires show enhnce Young s moulus (7.7 GP) n frcture strength (40 MP), while keeping consierle frcture elongtion ( ~ 5.8 % ; Fig. 8 ). This enhnce strength coul e scrie to the stronger Intensity (.u.) 5 0 5 0 5 30 35 40 θ (Degree) Tensile strength (MP) 40 0 00 80 60 40 0 0 0 3 4 5 6 7 8 9 0 Strin (%) Figure 8 X-ry iffrction ptterns n typicl mechnicl mesurements uner tensile loing of GO n grphene fires. X-ry iffrction ptterns ( ) n typicl mechnicl mesurements uner tensile loing ( ) of GO n grphene fires. The numer n enote grphene n GO fires, respectively. The strin rte is 5 % min. The Young s mouli of GO n grphene fires t low eformtion re out 5.4 n 7.7 GP, respectively. interctions etween grphene sheets resulting from the more compct stcking (smll interlyer istnce from Fig. 8 ) for the grphene fire. Although our fires re fr weker thn the iniviul grphene sheets (Young s moulus.0 TP n frcture strength 30 GP 3 ), we elieve tht the mechnicl property cn e gretly improve y optimiztion of the spinning process n post nneling to ecrese the vois in fires n then enhnce interctions etween the grphene sheets. Similr to GO fires, the crumle grphene sheets cn e stretche uner tensile stress, leing to the high frcture elongtion for the grphene fire (see the surfce n frcture morphology in Fig. 7e ; Supplementry Fig. S ). No rekge occurs when the fire is curve to tightene knot ( Fig. 7f ), showing the flexiility of net grphene fires. In ition, we use the flexile grphene fires to emroier ptterns in other textiles (for exmple, Chinese chrcter, ZHONG, in Fig. 7g ), n to wve pure grphene textiles or mixe ones with commercil 6
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 ARTICLE thres ( Fig. 7h ). These grphene-se fires n textiles shoul hve promising pplictions in electromgnetic shiels, ntenns n tteries. Discussion Recently, some exotic phse ehviours hve een oserve in the liqui crystlline system of symmetricl D collois, such s in empty liquis 37 n in ixil LCs 38, inicting the flui physics of D collois is still growing with vrious unknown mesophses espite the pst 70 yers 4. Herein, we foun tht D collois cn form CLC phse y using the prototype of GO sheets. With the help of synchrotron SAXS mesurements, we hve isclose two ifferent rrngements in GO ispersions, epening on the concentrtion: orienttionl orer n lmellr ttriutes, which re ssigne to the nemtic n chirl mesophses, respectively. Theoreticlly, Lnu Peierls instility in the system with the D ensity wve in D liqui meium exhiits qusi-long-rnge orer in smectic phses, rther thn in the true-long-rnge orer, cuse y the therml fluctution 7. Experimentl results hve emonstrte tht the positionl correltion function ecy lgericlly s some power of the istnce in smectic-a mesophse 39 4. To further explin the orerings in GO CLCs, Clli é lineshpe nlyses (see Supplementry Note ) were crrie out to the first scttering pek ( q 0 ) in SAXS profiles. We oserve tht the scttering intensity lso oeys the power-lw ecy s function of scttering vectors (S(0, 0, q ) ~ (q q 0 ) + η, η the Clli é exponent), implying the lmellr structures of GO CLCs. In single GO sheet, ll the toms involve re covlently one, n thus the sheet hs n extremely high Young s moulus (experimentl vlue for the chemiclly converte grphene 0.5 TP 4 ). We estimte tht the Young s moulus multiplies y the verge re of GO sheets ( w = 0.8 ± 0.3 μm) to mke the vlue of elstic moulus ( K =.6 ± 0.5 0 4 N), out five orers of mgnitue higher thn tht of self-ssemle ilyers without ny intermoleculr covlent oning in the conventionl smectic phse 39. By fitting the scttering profiles, we otine the Clli é exponents η s of GO CLCs with grient φ s from. to 0.38 %. Derive from the equtions () n () 39 4, h= qkt 0 B / 8p( BK) / x = ( K / B) / 4 () () where k B is the Boltzmnn constnt (.38 0 3 JK ), B the compression moulus, T the thermoynmic temperture (98 egree Kelvin for our smples), ξ correltion length for the fluctution (for the istnce longer thn ξ, the lyer height fluctutions re coherent from lyer to lyer, wheres for istnce smller thn ξ, fluctutions re single lyer n incoherent 4 ), we further otine the corresponing correltion lengths ( ξ s) of GO CLCs tht rnge from 6.4 ± 5.7 to 589.5 ± 93.0 μ m (etil fitting n quntittive nlysis re given in Supplementry Note n Tle S ). These clculte correltion lengths re gint, roun four orers of mgnitue longer thn tht in the conventionl smectic phse of smll molecules 4, implying tht there re little therml fluctution in GO CLCs. This effect is minly ttriute to the rigi, soli-like structure of iniviul GO sheet. The lmellr structures hve lso een oserve previously in the suspensions of soli-like, single colloil pltelets with very little therml fluctution 9,0. It is worth pointing out tht more effort is neee to put on the specific theory moel n computer simultion on LCs of D collois, s the soli flkes hve essentilly ifferent ntures from the conventionl ilyers noncovlently ssemle from smll molecules or lipis. Importntly, we hve etecte tht GO LCs egin to exhiit CD ctivity from φ > 0.38 %, n the opticl ctivity is significntly enhnce with incresing φ. In the comintion of CD inctivity in the filtrte GO films with uniform lmellr structure ( Fig. 3 ), we speculte tht the oserve opticl ctivity origintes from the twist isloctions of the lmellr structure in GO CLCs. To ssess the mjor role of electrosttic repulsion in the formtion of CLC, we hve investigte oth structures (y SAXS) n CD ctivities of GO ispersions with grient slt concentrtions. With enhncing the screening effect cuse y the stronger ionic strength of higher slt concentrtion, the wekene repulsive interction etween the sl plnes of GO sheets rought the stepwise compression of the lmellr structure (with ecresing interlyer spcing), n the wekene repulsive interction etween GO sheets ounries inuce the fe opticl ctivity ( Figs e n 3 ). Therefore, the electrosttic interction in GO CLCs is the ominte force n contriutes to this new phse ehviour. Owing to the similr POM textures etween our GO CLC n TGB phse, we offere twist-lmellr-lock moel to explin the ntures of the CLC of D collois, holing lmellr n helicl structurl ttriutes simultneously ( Fig. 5 ). Moreover, the fingerprint textures ( Fig. 4g i ) n nnul ring-like frcture structures ( Fig. 4 f ) re in ccornce with this moel. Following with the first exposl of CLC for D collois, more CLCs of D collois (for exmple, clys) will e proly unveile in the future, to enrich our unerstnings on colloil LC regime, which will in turn oost the cretion of new mterils. In ition, this iscovery lso clls for the construction of theoreticl moel for CLC of D collois. It is known tht one of the most importnt pplictions of lyotropic LCs is to mke mcroscopic fires y wet-spinning technology. Up to te, liner, rigi polymers such s romtic polymies s well s D nnowires, such s CNTs, hve een successfully spun into strong n continuous fires from their LC opes 4 6, ue to the noncovlent chemicl ons (for exmple, vn er Wls forces n hyrogen onings) n strong mechnicl chin entnglements or interconnection mong ifferent tues. Even though LCs of D collois hve een reporte for severl eces, however, mcroscopic fires me from net D pltes hve never een chieve previously, prtly ecuse the interctions etween soli-like flkes re wek, n prtly ecuse the soluility of collois is not high enough for continuous spinning. We hve emonstrte tht highly solule grphene sheets, typicl moel of D collois, cn e reily spun into continuous n roust fires from their LC ispersions. The sheet lignment inherite from the intrinsic lmellr orer of LCs provies strong interctions etween contcte sheets tht re responsile for the strong mechnicl strength of grphene fires, n the loclly crumle structures of iniviul sheets mke the grphene fires flexile. The integrtion of high conuctivity, excellent mechnicl property n unique ttriutes ssocite with grphene mkes the fires highly ttrctive in mny pplictions such s functionl textiles n chemicl sensors. The inustrilly vile wet-spinning technique provies novel pproch to friction of cron fires from nturl grphite. In our ner term, prticulrly promising pplictions of GO LCs s useful hosts re mcroscopic grphene-se fires with iversiform guests such s polymers, nnocrystls n CNTs; such new mterils woul e wiely useful in the fiels of high-performnce fires, energy storge n fuel cells. Inspire y the concept of continuous fires me from grphene sheets, we elieve tht the possile LCs of other D collois (such s montmorillonite 4, metllic sheets 43, MoS, BN n other D nnosheets 44 ) cn e wet-spun into mcroscopic fires with unique properties for mny promising pplictions. Methos Preprtion of nrrowly isperse GO smples. GO sheets were prepre y the protocol escrie previously. The isopycnic ifferentil centrifugtion ws performe on the GO ispersion ( φ = 0.075 % ). After the centrifugtion t 5,000 r. p.m. for h, the ottom gel is the clssifie GO smple, n the superntnt ws processe for the successive centrifugtion. Through repeting process t respective spees of 0,000 n 5,000 r.p.m. (3,300 g ) for h, we otine two corresponing clssifie smples n took the smple (t 5,000 r.p.m.) with the smllest 7
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 with for investigtions in this stuy. GO ispersions (5 ml) were freeze-rie for ys n then further rie t room temperture uner vcuum for 5 ys n their mss frctions ( f m ) were otine. The volume frction ( φ ) is clculte y: φ f m /ρ GO, where ρ GO is the GO ensity tht is estimte to e.3 g cm 3. Silic-se chirl gel film. The silic-se chirl gel ws prepre y cross-linking of tetrethyl orthosilicte uner wek sic surrouning, using CLC of GO s the templte. We introuce ml tetrethyl orthosilicte into ml methnol / wter solution of GO (vol methonl :vol wter = 9:, φ = 0.38 % ), n stirre for h to get homogeneous solution. After injecting few rops of mmoni solution (ph = ) n stirring, the mixture ws loe into circulr isc with imeter of 3 cm, n kept t room temperture for 4 h. Finlly, we otine the self-stning, silicse gel film with CD ctivity. Preprtion of GO n grphene fires. During the spinning process for GO fires ( Supplementry Fig. S9 ), the GO ispersions were loe into glss syringes n injecte into the NOH / methnol solution uner.5 MP hel y N. The fires in the cogultion th were rolle onto the rum, wshe y methnol to remove the slt n rie for 4 h uner room temperture. The chemiclly converte grphene fires were prepre y chemicl reuction of s-prepre GO fires in the queous solution of hyroioic ci (40 % ) t 80 C for 8 h, followe y wshing with methnol n vcuum rying for h. Instruments. Atomic force microscopy imges were tken in the tpping moe y crrying out on NSK SPI3800, with smples prepre y spin-coting GO ispersions onto freshly cleve mic sustrtes t 000 r.p.m. SEM imges were tken on Hitchi S4800 fiel-emission SEM system. Cryo-SEM imges were tken on Hitchi S3000N equippe with cryotrnsfer. The liqui smple ws roppe into the cvity, loe into liqui nitrogen, trnsferre into the cryotrnsfer n the smple ws cut y le. The frcture ws sulime for h efore imging. SAXS tests were crrie out in the Shnghi Synchrotron Rition Fcility, using fixe wvelength of 0.4 nm, smple-to-etector istnce of 5 m n n exposure time of 600 s. The D scttering ptterns were collecte on chrge couple evice cmer, n the curve intensities versus q were otine y integrting the t from the ptterns. POM oservtions were performe with Nikon E600POL n the liqui smples were loe into the plnr cells for oservtions. CD spectr were collecte on Bio-Logic MOS-450 spectrometer, n the smples were injecte into the cell with thickness of 0.5 cm. Confocl oservtions were performe on Zeiss Lsm50 microscopy, using 488-nm lser to excite with filtrte roun 560 nm. The mesurement of zet potentil ws performe on Mlvern ZET- 3000HS pprtus. The conuctivity of chemiclly reuce fires ws mesure y t wo - pro e re s ist iv it y- me su r i ng i nst r u me nt. References. Strzeleck, T. E., Dvison, M. W. & Rill, R. L. Multiple liqui crystl phses of DNA t high concentrtions. Nture 33, 457 460 (988 ).. 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Steric interctions in moel multimemrne system : synchrotron X-ry stuy. Phys. Rev. Lett. 57, 78 7 (986 ). 4. L e i, N., S finy, C. R. & Bruinsm, R. F. Discrete hrmonic moel for stcke memrnes: theory n experiment. J. Phys. II Frnce 5, 55 63 (995 ). 4. Gómez-Nvrro, C., Burghr, M. & Kern, K. Elstic properties of chemiclly erive single grphene sheets. Nno Lett. 8, 045 049 (008 ). 4 3. Hu ng, X. et l. Synthesis of hexgonl close-pcke gol nnostructures. Nt. Commun., 9 (0 ). 4 4. C ol e mn, J. N et l. Two-imensionl nnosheets prouce y liqui exfolition of lyere mterils. Science 33, 568 57 (0 ). Acknowlegements We thnk Professor S.F. Chen, Dr H.Q. Zho, Dr Y.Z. Jin n Dr M. Hnif for the helpful iscussions n the stffs in the Shnghi Synchrotron Rition Fcility for SAXS chrcteriztions. This work is fune y the Ntionl Nturl Science Fountion of Chin (0974093 n 5736), Ntionl Key Bsic Reserch Progrm of Chin (007CB936004), Qinjing Tlent Fountion of Zhejing Province (00R00), Funmentl Reserch Funs for the Centrl Universities (009QNA4040), Reserch Fun for the Doctorl Progrm of Higher Euction of Chin (00000049) n Zhejing Provincil Nturl Science Fountion of Chin (00000049). 8
NATURE COMMUNICATIONS DOI: 0.038/ncomms583 Author contriutions Z.X. n C.G. conceive n esigne the reserch, nlyse the experimentl t n wrote the pper; Z.X. conucte the experiments; C.G. supervise n irecte the project. Aitionl informtion Supplementry Informtion ccompnies this pper t http://www.nture.com/ nturecommunictions Competing finncil interests: The uthors eclre no competing finncil interests. ARTICLE Reprints n permission informtion is ville online t http://npg.nture.com/ reprintsnpermissions/ How to cite this rticle: Xu, Z. & Go, C. Grphene chirl liqui crystls n mcroscopic ssemle fires. Nt. Commun. :57 oi: 0.038 / ncomms583 (0). License: This work is license uner Cretive Commons Attriution-NonCommercil- Shre Alike 3.0 Unporte License. To view copy of this license, visit http:// cretivecommons.org/licenses/y-nc-s/3.0/ 9