ebook img

Microstructures and mechanical performance of polyelectrolyte/nanocrystalline TiO2 nanolayered composites. PDF

2.4 MB·English
by  ZhangBin
Save to my drive
Quick download
Download
Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.

Preview Microstructures and mechanical performance of polyelectrolyte/nanocrystalline TiO2 nanolayered composites.

Zhangetal.NanoscaleResearchLetters2013,8:44 http://www.nanoscalereslett.com/content/8/1/44 NANO EXPRESS Open Access Microstructures and mechanical performance of polyelectrolyte/nanocrystalline TiO 2 nanolayered composites Bin Zhang1*, Hai-Feng Tan1,2, Jia-Wei Yan2, Ming-Dong Zhang1, Xu-Dong Sun1 and Guang-Ping Zhang2* Abstract Biological materials with hierarchicallylaminated structures usually exhibit a good synergy between strength and fracture toughness. Here, we showthata bio-inspired (polyelectrolyte (PE)/TiO ) nanolayered composite with a 24 thickness ratio of TiO and amorphous PE layers ofabout 1.1 has been prepared successfully on Sisubstrates by 2 layer-by-layer self-assembly and chemical bath deposition methods. Microstructures of thenanolayered composite were investigated by scanning electron microscopy, secondaryion mass spectroscopy,and high-resolution transmission microscopy. Mechanical performance of thecompositewas characterized byinstrumented indentation.Thecompositeconsistingof17.9-nm-thicknanocrystallineTiO and16.4-nm-thickamorphousPElayers 2 hasastrengthofabout245MPa,whichisclosetothatofshells,whilethefracturetoughnessofthecomposite,K = IC 1.62±0.30MPa·m1/2,isevidentlyhigherthanthatofthebulkTiO .Apossiblestrategytobuildthecompositeat 2 nanoscaleforhighmechanicalperformancewasaddressed. Keywords:Bio-inspirednanolayeredcomposite,Layer-by-layerself-assembly,Chemicalbathdeposition,Mechanical property Background insensitive to flaws, i.e., the strength of a perfect mineral Biological materials (such as bones or shells, etc.) with platelet was maintained despite defects. This intrigued us multiscale and hierarchical structures consisting of thick, to design and synthesize the artificial counterparts of this hard inorganic mineral layers and thin, soft organic layers compositewithnanometer-thickconstituentlayerslessthan exhibit an excellent combination of strength and tough- 30nm. ness [1,2]. Although a number of metallic multilayered/ In this work, a variation method of combination of tra- laminated composites produced by various methods [3,4] ditionalchemicalbathdeposition(CBD)[10,13]andlayer- hadrevealedahighstrengthandapotentialimprovement by-layer (LBL) self-assembly [14] methods was conducted ofplasticitywithoutlosingstrengthowingtothecontri- topreparealayeredstructurestackedalternatelybynano- bution of the laminated structures and interfaces [5], a crystallineTiO andpolyelectrolyte(PE)layerswiththick- 2 feweffortshadbeenmadetodesignandsynthesizebio- nesses less than 30 nm. Microstructures and mechanical mimetic laminated materials with submicron-thick in- properties of the nanolayered composites (NLCs) were organic layers [6-11]. Theoretically, Gao et al. [12] investigated. demonstrated that when the critical length scale of the mineral inorganic platelets in natural materials drops Methods below approximately 30 nm, the biomaterials became Silicon (001) substrates (3×10 mm2) were immersed in Piranha solution [15] for 20 min at 60°C after ultrasonic *Correspondence:[email protected];[email protected] cleaning in acetone. A negatively charged hydrophilic Si- 1KeyLaboratoryforAnisotropyandTextureofMaterials(Ministryof Education),NortheasternUniversity,3-11WenhuaRoad,Shenyang110819, OHlayerwasformedontheSisurface.Owingtotheelec- People'sRepublicofChina trostatic attraction of oppositely charged polyions, three 2ShenyangNationalLaboratoryforMaterialsScience,InstituteofMetal different PEs, poly(ethyleneimine) (PEI), poly(sodium 4- Research,ChineseAcademyofSciences,72WenhuaRoad,Shenyang110016, People'sRepublicofChina styrenesulfonate)(PSS),andpoly(allylaminehydrochloride) ©2013Zhangetal.;licenseeSpringer.ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommons AttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,andreproduction inanymedium,providedtheoriginalworkisproperlycited. Zhangetal.NanoscaleResearchLetters2013,8:44 Page2of5 http://www.nanoscalereslett.com/content/8/1/44 (PAH),wereselectedaspolycation,polyanion,andpolyca- TI 900, Eden Prairie, MN, USA) with a Berkovich tip (tip tion, respectively, and the organic polymer layers were radius approximately 50 nm) was used to determine the assembled by LBL deposition [14] of the three different hardness (H) and modulus (E) of the NLCs at a constant PEs. The negatively charged Si substrates (after Piranha loading rate of 20 μN/s at room temperature. The mean treatment) were alternately immersed into the three dif- values of H and E were then obtained at an indentation ferent PE solutions in the sequence (PEI/PSS)(PAH/PSS) depthof10%to20%wholethicknessoftheNLCinorder 3 [10,14],andtheimmersionintherespectivepolymersolu- to eliminate substrate effects [16]. Microindentation tests tions was at room temperature for 20 min. A positively (LECO AMH43, St. Joseph, MI, USA) were conducted to charged surface was formed by adsorption of PEI on sili- evaluate fracture toughness of the NLCs following the con since PEI can givegood coveringof oxidizedsurfaces methodproposedbyXiaetal.[17]. [14]. The thickness of the PE layers wascontrolled by the number of dipping cycles into PAH/PSS solutions, while Results and discussion three dipping cycles were carried out in the present work Microstructures to ensure the thickness of the PE layers to be less than A scanning electron microscopy (SEM) observation 30 nm. Deposition of inorganic TiO layers onto the PE (Figure1a) shows that the surface ofthe (PE/TiO ) NLC 2 2 4 surfacewasaccomplishedina10mMsolutionoftitanium isquitesmooth.Acrackingregioncausedbya scratching peroxo complex (TiO2+) and 30 mM HCl by the CBD of a needle reveals that the NLC is a typical multilayered 2 procedure [10]. In order to ensure the thickness of the structure with four layers, as indicated by arrows in deposited TiO layer to be less than 30 nm, the adopted Figure 1b. The surface morphology of the NLC examined 2 deposition time and temperature were 2 h and 60°C, re- byatomicforcemicroscopy(Figure1c)showsthatthetop spectively.ThePE/TiO NLCswithfourbilayeredperiods TiO layer is a densely packed spherical particle with a 2 2 ((PE/TiO ) ) were prepared finally by sequentially apply- diameter of approximately 40 nm. The surface roughness 2 4 ingtheLBLself-assemblyandtheCBDtechniques. ofthetopTiO layerisabout4.5nm(Figure1d). 2 Secondary ion mass spectroscopy (SIMS; ION-TOF SIMS characterizations of the intensity variations of the TOF.SIMS 5, Münster, Germany) was utilized to deter- ejected secondary ions of the present elements as a func- mine the existence of Ti, O, C, and Si ions, as a function tion of sputtering time of the primary ion beam exhibit ofdepthbelowthefilmsurface.Ananoindenter(Hysitron thatthereisaperiodicalvariationoftheintensityofOion Figure1SEMobservations,AFMcharacterization,andsurfaceroughnessofthenanocomposite.SEMobservationsonsurfaceofthe(PE/TiO) 24 nanolayeredcomposite:(a)surfacemorphologyand(b)layerstructure.(c)AFMcharacterizationofsurfaceofthenanocomposite.(d)Surface roughnessofthenanocompositemeasuredbyAFM. Zhangetal.NanoscaleResearchLetters2013,8:44 Page3of5 http://www.nanoscalereslett.com/content/8/1/44 and Ti ion with the sputtering time (Figure 2), while the intensity of C ion exhibits an inverse periodical variation with the sputtering time. After the appearance of four peaks of the periodical variation of the elements, the in- tensityoftheTiandCionsbecomesdecreased,whilethat of the Si ion becomes strong and finally reaches a cer- tain intensity level, indicating the appearance of the Si substrate. The profile clearly demonstrates the presence of a multilayered structure of alternating TiO -enriched 2 and C-enriched layers, i.e., the existence of an ordered composite structure of well-defined inorganic and or- ganiclayers. A transmission electron microscopy (TEM) cross- sectional observation at a low magnification (Figure 3a) also clearly reveals the multilayered structure in the (PE/ TiO ) NLC,thoughthereisinterpenetrationbetweenthe 2 4 PEand TiO layers(seeFigure3b).TheorganicPElayers 2 appear as bright regions with an average thickness of 16.4 nm, while the inorganic TiO layers are visible as 2 dark regions with an average thickness of 17.9 nm esti- matedfromTEMcross-sectionalimages.Thus,thethick- ness ratio (R) of the TiO layer to the PE layer is about t 2 1.1.AhighmagnificationofthePE/TiO NLC(Figure3b) 2 shows that the interface between the PE and TiO layers 2 is not sharp completely, but somewhat diffuse, indicating a sizeable interpenetration between theTiO and organic 2 PE components [10]. A selected-area electron diffraction pattern taken from the dotted-circle region in Figure 3a was presented in the inset of Figure 3b, revealing the dif- fuse diffraction ring corresponding to the amorphous PE layers, while some diffraction spots exhibit the existence ofcrystallites.Ahigh-resolutiontransmissionelectronmi- croscopy (HRTEM) image (Figure 3c) shows that some nanocrystallines (NCs) with different orientations have Figure3TEMcross-sectionalimagesofthecompositeand HRTEMimageoftheinterface.TEMcross-sectionalimagesofthe (PE/TiO ) nanolayeredcompositeat(a)lowmagnificationand 24 (b)highmagnification.(c)HRTEMimageofinorganicTiO layer 2 andorganic/inorganicinterface. formed in theTiO layer and their sizes are in a range of 2 about 5 to 15 nm. The NC TiO might form during the 2 CBD process rather than the TEM electron-beam irra- Figure2SIMScharacterizations.Variationoftheintensityof diation since the TEM accelerating voltage we used was ejectedsecondaryionsofthepresentelementsasafunctionof 200 keV rather than 400 keV [10]. The formation of the sputteringtimeofprimaryionbeamcharacterizedbysecondaryion NC TiO might be related to the very thin TiO layers massspectroscopy. 2 2 (approximately17.9nm)depositedinashorttime(2h)of Zhangetal.NanoscaleResearchLetters2013,8:44 Page4of5 http://www.nanoscalereslett.com/content/8/1/44 theCBDprocess.Inaddition,theroughandthinPElayers indentation depth of about 22 nm. Young's modulus of assembled by few numbers of cycles (3 cycles) for the theNLCdeterminedfromthecontactareaandtheelastic PAH/PSSmightalsoplayanimportantroleinthehetero- contact stiffness [16] is 17.56±1.35 GPa, which is much geneousnucleationoftheTiO nanocrystallines. lowerthanthatofthenacre(E=50GPa)[18].Suchalow 2 Young's modulus may be attributed to the large volume fraction of organic PElayersdue to R ≈1.1.Based on the t ruleofmixture,Young'smodulusisestimatedtobeabout MFigeuchrean4iacaslhpoewrfsoarmtyapnicceal load-indentation depth curve of 16.74 GPa by using ETiO2 = 27.5 GPa and EPE=5 GPa [11], and this is close to the experimental result of the the (PE/TiO ) NLC. In the loading stage, no pop-in be- 2 4 (PE/TiO ) NLC (17.56 GPa). The mean hardness of the 24 havior was detected, indicating that the NLC can be (PE/TiO ) NLC determined by nanoindentation is 24 deformed continuously to the indentation depth of about 0.73 GPa with a standard deviation of 0.09 GPa. Using a 30 nm. In the unloading stage, the initially linear unload- general relation between hardness (H) and strength (σ) ing reveals an elastic recovery. With a further unloading, found in a lot of materials, σ≅H= , the mean strength of 3 the nonlinear variation of the load with the displacement theNLCwascalculatedasabout245MPa,whichisquite reveals the non-elastic recovery, leading to a residual close to the strength of shells reported in the literature (100to300MPa)[10,18].AlthoughR ≈1.1,itisexpected t thattheNC TiO layerswouldalsocontributetothehigh 2 strengthofthecomposite. Following the method to determine the fracture tough- ness(K )ofathinfilmbondedtoabrittlesubstrate[17], IC when the indentation load was large enough applied to the Si substrate uncoated by the (PE/TiO ) NLC, micro- 2 4 cracks initiated from four corners of the indent in the Si substrate and advanced into the (PE/TiO ) nanolayer- 2 4 coated region, as indicated by an arrow in Figure 4b. Based on the measurements of the crack length, K of IC the (PE/TiO ) NLC was obtained as K =1.62± 2 4 IC 0.30 MPa·m1/2, which is almost a threefold increase in comparison to that of the single TiO layer of approxi- 2 mately 400 nm thick [11]. One reason for the enhance- ment of K of the present NLC was attributed to energy IC dissipationviacrackdeflectionalongtheinorganic/organic interface, as a general mechanism operated in artificial and natural multilayered architectures [11]. Furthermore, since the present (PE/TiO ) NLC has an inorganic/ 24 organic layer thickness ratio of about 1.1 and the TiO 2 thicknessisonly17.9nm,itisbelievedthatevenifacrack initiatesintheTiO layerwithathicknessof17.9nm,the 2 NLC would become more insensitive to flaws, as pre- dicted by Gao et al. [12]. The hierarchical structures in biological materials have shown a good synergy of high strength and good fracture toughness (damage tolerance). Li et al. [19] have revealed that the mineral layer in the nacre consists of nanocrystalline CaCO platelets, which 4 facilitates grain boundary sliding. This also implies the possible activation of the grain boundary sliding mecha- nism in our NC TiO layers during deformation. The Figure4Load-indentationdepthcurveofthecompositeand 2 present results indicate that building the composite con- SEMimageoftheindentation-inducedmicrocrack.(a)Load- indentationdepthcurveofthe(PE/TiO2)4nanolayeredcomposite sisted of the amorphous PE and the NC TiO2 layers at measuredbynanoindentation.(b)SEMimageshowingthat nanometer scales may provide a possible strategy toward indentation-inducedmicrocrackadvancedintothe(PE/TiO2)4 enhancing damage tolerance of the material even if the nanolayer-coatedregion,bywhichfracturetoughnessofthe best optimum ratio of the organic layer to the NC inor- nanocompositecanbeobtained. ganiclayerstillneedstobefound. Zhangetal.NanoscaleResearchLetters2013,8:44 Page5of5 http://www.nanoscalereslett.com/content/8/1/44 Conclusions 13. BillJ,HoffmannRC,FuchsTM,AldingerF:Depositionofceramicmaterials The bio-inspired (PE/TiO ) nanolayered composite with fromaqueoussolutioninducedbyorganictemplates.ZMetallkd2002,93:12. 24 14. DecherG:Fuzzynanoassemblies:towardlayeredpolymeric an inorganic/organic layer thickness ratio of about 1.1, multicomposites.Science1997,277:1232–1237. which consisted of nanocrystalline TiO2 and amorphous 15. SeuKJ,PandeyAP,HaqueF,ProctorEA,RibbeAE,HovisJS:Effectof PElayerswiththicknessesof17.9and16.4nm,respectively, surfacetreatmentondiffusionanddomainformationinsupportedlipid bilayers.BiophysJ2007,92:2445–2450. was prepared on a Si (001) substrate by LBL self-assembly 16. OliverWC,PharrGM:Measurementofhardnessandelasticmodulusby and CBD methods. The (PE/TiO2)4 nanocomposite has a instrumentedindentation:advancesinunderstandingandrefinements strength of about 245 MPa, being close to that of the na- tomethodology.JMaterRes2004,19:3–20. 17. XiaZ,CurtinWA,SheldonBW:Anewmethodtoevaluatethefracture turalshell,whilethefracturetoughnessofthenanocompo- toughnessofthinfilms.ActaMater2004,52:3507–3517. site, KIC=1.62±0.30 MPa·m1/2, is evidently higher than 18. JiBH,GaoHJ:Mechanicalpropertiesofnanostructureofbiological thatofthesingleTiO ofabout400nmthick. materials.JMechPhysSolid2004,52:1963–1990. 2 19. LiXD,XuZH,WangRZ:Insituobservationofnanograinrotationand deformationinnacre.NanoLett2006,6:2301–2304. Abbreviations CBD:Chemicalbathdeposition;LBL:Layer-by-layer;NC:Nanocrystalline; NLC:Nanolayeredcomposite;PE:Polyelectrolyte. doi:10.1186/1556-276X-8-44 Citethisarticleas:Zhangetal.:Microstructuresandmechanical performanceofpolyelectrolyte/nanocrystallineTiO nanolayered Competinginterests 2 composites.NanoscaleResearchLetters20138:44. Theauthorsdeclarethattheyhavenocompetinginterests. Authors’contributions Allauthorscontributedequallytothiswork.BZ,XDS,andGPZconceivedthe project.BZ,HFT,andMDZperformedtheexperiments.JWYperformedthe TEMobservations.Allauthorsanalyzedthedata,discussedtheresults,and wrotethepaper.Allauthorsreadandapprovedthefinalmanuscript. Acknowledgements ThisworkwassupportedbytheNationalBasicResearchProgramofChina (grantno.2010CB631003)andpartiallysupportedbytheNationalNatural ScienceFoundationofChina(grantnos.51171045and51071158). Received:20November2012Accepted:6January2013 Published:21January2013 References 1. FratzlP:Bonefracture-whenthecracksbegintoshow.NatMater2008, 7:610–612. 2. JacksonAP,VincentJFV,TurnerRM:Themechanicaldesignofnacre. ProcRSocLondBBiolSci1988,234:415–440. 3. LesuerDR,SynCK,SherbyOD,WadsworthJ,LewandowskiJJ,HuntWH: Mechanicalbehaviouroflaminatedmetalcomposites.IntMaterRev1996, 41:169–197. 4. BouazizO,BrechetY,EmburyJD:Heterogeneousandarchitecturedmaterials: apossiblestrategyfordesignofstructuralmaterials.AdvEngMater2008, 10:24–36. 5. SynCK,LesuerDR,CadwellKL,SherbyOD,BrownKR:Laminatedmetal compositesofultrahighcarbon-steelbrassandAl/Al-Sic-processing andproperties.InDevelopmentsinCeramicandMetal-MatrixComposites: Proceedingsofthe1992AnnualMeetingoftheMinerals,MetalsandMaterials Society,SanDiego,CA.EditedbyUpadhyaK.Warrendale:Minerals,Metals andMaterialsSociety;1991:311–322. 6. SellingerA,WeissPM,NguyenA,LuYF,AssinkRA,GongWL,BrinkerCJ: Continuousself-assemblyoforganic–inorganicnanocompositecoatings thatmimicnacre.Nature1998,394:256–260. 7. TangZY,KotovNA,MagonovS,OzturkB:Nanostructuredartificialnacre. NatMater2003,2:413–418. Submit your manuscript to a 8. SanchezC,ArribartH,GuilleMMG:Biomimetismandbioinspirationas journal and benefi t from: toolsforthedesignofinnovativematerialsandsystems.NatMater2005, 4:277–288. 7 Convenient online submission 9. DevilleS,SaizE,NallaRK,TomsiaAP:Freezingasapathtobuildcomplex composites.Science2006,311:515–518. 7 Rigorous peer review 10. BurghardZ,TucicA,JeurgensLPH,HoffmannRC,BillJ,AldingerF: 7 Immediate publication on acceptance Nanomechanicalpropertiesofbioinspiredorganic–inorganic 7 Open access: articles freely available online compositefilms.AdvMater2007,19:970–974. 7 High visibility within the fi eld 11. BurghardZ,ZiniL,SrotV,BellinaP,vanAkenPA,BillJ:Toughening throughnature-adaptednanoscaledesign.NanoLett2009,9:4103–4108. 7 Retaining the copyright to your article 12. GaoHJ,JiBH,JagerIL,ArztE,FratzlP:Materialsbecomeinsensitiveto flawsatnanoscale:lessonsfromnature.ProcNatlAcadSciUSA2003, Submit your next manuscript at 7 springeropen.com 100:5597–5600.

See more

The list of books you might like

Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.