this work provides an important advance in quan-titative network theory and a foundation forfurther development of theories that account forinteracting network defects and entanglements.Combining RENT with primary and higher-

order loop measurements provides quantitativeagreement with measured elastic moduli for net-works with compositions and structures that arerelevant to common applications. In other words,RENT can predict the bulk mechanical propertiesof polymer networks on the basis of molecularinformation. We anticipate that RENT and loop-counting methods will be applicable to a widerange of polymer networks.

REFERENCES AND NOTES

1. E. J. Mittemeijer, in Fundamentals of Materials Science: TheMicrostructure-Property Relationship Using Metals as ModelSystems (Springer, 2011), pp. 201–244.

2. P. Capper, Ed., Bulk Crystal Growth of Electronic, Optical &Optoelectronic Materials (Wiley, 2010).

3. K. Müllen, Nat. Rev. Mater. 1, 15013 (2016).4. P. J. Flory, J. Chem. Phys. 66, 5720 (1977).5. M. Rubinstein, R. H. Colby, Polymer Physics (Oxford Univ.

Press, 2003).6. G. Hild, Prog. Polym. Sci. 23, 1019–1149 (1998).7. D. R. Miller, C. W. Macosko, Macromolecules 9, 206–211 (1976).8. M. Mooney, J. Appl. Phys. 11, 582 (1940).9. S. K. Patel, S. Malone, C. Cohen, J. R. Gillmor, R. H. Colby,

Macromolecules 25, 5241–5251 (1992).10. M. Rubinstein, S. Panyukov, Macromolecules 30, 8036–8044

(1997).11. Y. Akagi et al., Macromolecules 44, 5817–5821 (2011).12. Y. Akagi, J. P. Gong, U.-i. Chung, T. Sakai, Macromolecules 46,

1035–1040 (2013).13. R. F. T. Stepto, in Biological and Synthetic Polymer Networks,

O. Kramer, Ed. (Springer, 1988), pp. 153–183.14. S. Dutton, R. F. T. Stepto, D. J. R. Taylor, Angew. Makromol. Chem.

240, 39–57 (1996).15. K. Dušek, M. Dušková-Smrčková, J. Huybrechts, A. Ďuračková,

Macromolecules 46, 2767–2784 (2013).16. R. F. T. Stepto, J. I. Cail, D. J. R. Taylor, Mater. Res. Innovat. 7, 4

(2003).17. H. Zhou et al., Proc. Natl. Acad. Sci. U.S.A. 109, 19119–19124

(2012).18. H. Zhou et al., J. Am. Chem. Soc. 136, 9464–9470 (2014).19. K. Kawamoto, M. Zhong, R. Wang, B. D. Olsen, J. A. Johnson,

Macromolecules 48, 8980–8988 (2015).20. A. C. Balazs, Nature 493, 172–173 (2013).21. R. Wang, A. Alexander-Katz, J. A. Johnson, B. D. Olsen, Phys.

Rev. Lett. 116, 188302 (2016).22. See supplementary materials on Science Online.23. H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. Int. Ed.

40, 2004–2021 (2001).24. J. A. Johnson et al., J. Am. Chem. Soc. 128, 6564–6565 (2006).25. G. S. Grest, M. Pütz, R. Everaers, K. Kremer, J. Non-Cryst.

Solids 274, 139–146 (2000).26. G. S. Grest, K. Kremer, E. R. Duering, Eur. Phys. Lett. 19,

195–200 (1992).27. R. F. T. Stepto, Polymer 20, 1324–1326 (1979).

ACKNOWLEDGMENTS

We thank C. N. Lam and S. Tang for help with Teflon mold fabrication.Supported by NSF grant CHE-1334703 (J.A.J. and B.D.O.), theInstitute for Soldier Nanotechnologies via U.S. Army Research Officecontract W911NF-07-D-0004 (B.D.O.), and NSF Materials ResearchScience and Engineering Centers award DMR-14190807. All data areavailable in the supplementary materials. Author contributions:M.Z., R.W., K.K., B.D.O., and J.A.J. designed the research; M.Z. andK.K. performed all experimental work; R.W. developed the theory; andM.Z., R.W., K.K., B.D.O., and J.A.J. wrote the paper.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/353/6305/1264/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S32References (28, 29)

29 April 2016; accepted 18 August 201610.1126/science.aag0184

NANOMATERIALS

1D nanocrystals with preciselycontrolled dimensions, compositions,and architecturesXinchang Pang, Yanjie He, Jaehan Jung, Zhiqun Lin*

The ability to synthesize a diverse spectrum of one-dimensional (1D) nanocrystals presentsan enticing prospect for exploring nanoscale size- and shape-dependent properties. Here wereport a general strategy to craft a variety of plain nanorods, core-shell nanorods, and nanotubeswith precisely controlled dimensions and compositions by capitalizing on functionalbottlebrush-like block copolymers with well-defined structures and narrow molecular weightdistributions as nanoreactors.These cylindrical unimolecular nanoreactors enable a high degreeof control over the size, shape, architecture, surface chemistry, and properties of 1D nanocrystals.We demonstrate the synthesis of metallic, ferroelectric, upconversion, semiconducting, andthermoelectric 1D nanocrystals, among others, as well as combinations thereof.

The synthesis of isotropic nanomaterials hasprovided access to an array of nanoparticleswith controlled sizes, shapes, and function-alities. Going beyond zero-dimensionalnanoparticles (1, 2), one-dimensional (1D)

nanocrystals such as nanorods (3), nanotubes (4),nanowires (5), and shish kebab–like heterostruc-tures (6, 7) exhibit a range of properties [e.g.,optical (8), electrical (9), magnetic (10), and cat-alytic (11)] depending on their size and shape.Emerging approaches, including template-assistedsynthesis (12–14), chemical vapor deposition (15),and colloidal synthesis (16), enable the prepara-tion of intriguing 1D nanocrystals with controlleddimensions. However, some of these proceduresrequire tedious multistep reactions and purifica-tion processes and rigorous experimental condi-tions; in addition, they are difficult to generalize.In contrast to previously reported polymer

brushes for the synthesis of nanowires (12), ourbottlebrush-like block copolymers (BBCPs) areunimolecular cylindrical polymer brushes thathave a cellulose backbone with densely graftedfunctional block copolymers as side chains (arms),which consist of multiple compartments (innerand intermediate blocks for templating nano-crystal growth and outer blocks for solubility).Cellulose forms a rigid backbone because of intra-molecular hydrogen bridges between hydroxylgroups and oxygen atoms (17). In addition, thethree substitutable hydroxyl groups on celluloseallow dense polymer side chains to be graftedfrom the cellulose backbone. We used these ad-vantages inherent in cellulose to synthesize ourstraight cylindrical BBCPs (figs. S1 to S8 and sup-plementary text, sections I to III). Each fam-ily of BBCPs was synthesized by sequentialatom transfer radical polymerization (ATRP)or ATRP followed by a click reaction (Fig. 1 andfigs. S9 to S11).

Plain nanorods of varied diameters and com-positions were synthesized using amphiphiliccellulose-g-(PAA-b-PS) {cellulose-graft-[poly(acrylicacid)-block-polystyrene]} BBCP nanoreactors (Fig.1A; table S2; and supplementary text, sectionsIII and IV). Because each unit in the cellulosebackbone enables the growth of three PtBA-b-PSdiblocks (upper left panel in Fig. 1A; supple-mentary text, sections I and II), the denselygrafted PtBA-b-PS arms in conjunction with therigidity of the backbone force the cellulose-g-(PtBA-b-PS) BBCP to adopt a straight, rigid, cy-lindrical conformation (upper right panel in Fig.1A) [PtBA, poly(tert-butyl acrylate)]. Subsequenthydrolysis of the PtBA blocks yields amphiphiliccellulose-g-(PAA-b-PS) with inner hydrophilic PAAblocks and outer hydrophobic PS blocks (lowerright panel in Fig. 1A and fig. S47).When cellulose-g-(PAA-b-PS) BBCPs are dispersed in dimethyl-formamide (DMF) polar solvent (18), the resultingunimolecularmicelles canbeused as nanoreactors.The interaction betweenhighly polar DMFand theinner PAA blocks is stronger than that betweenDMF and the outer PS blocks. Thus, there is agreater repulsion between PAA chains in DMFthan between PS chains (18). As a result, the PAAchains are greatly stretched and form a large com-partment. On addition and dispersion of inor-ganic precursors into the solution, the cylindricalcompartment containing PAA blocks can accom-modate a large volume of precursors. In additionto the solvent polarity effect noted above, the pre-cursors are also preferentially partitioned in thecylindrical PAA block compartment as a result ofthe strong coordination interaction between themetal moieties of precursors and the carboxylicacid groups of PAA, which creates a high enoughconcentration of precursors to initiate the nucle-ation and growth of inorganic nanorods (19) (figs.S38 to S46 and S71; see supplementary text, sectionIV, for the proposed formation mechanisms). Thein situ capping of PS chains on the nanorods facil-itates dispersion and solubility in various organicsolvents (lower left panel in Fig. 1A).

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School of Materials Science and Engineering, GeorgiaInstitute of Technology, Atlanta, GA 30332, USA.*Corresponding author. Email: zhiqun.lin@mse.gatech.edu

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As a proof of concept, we synthesized upcon-version NaYF4:Yb/Er nanorods. Transmissionelectron microscopy (TEM) images at differentmagnifications (Fig. 2A) demonstrate the forma-tion of uniform NaYF4:Yb/Er nanorods with anaverage diameterD of 9.8 ± 0.5 nm and length Lof 97 ± 9 nm. These nanorods are highly crys-talline andhave a hexagonal phase, as establishedby high-resolution TEM (HRTEM; Fig. 2A) andx-ray powder diffraction (XRD) measurements(fig. S60). Energy-dispersive x-ray spectroscopy(EDS) confirmed the composition of theNaYF4:Yb/Er nanorods (fig. S63). Thermogravimetric anal-ysis (TGA) showed that the volume percentage ofPAA blocks encapsulated by NaYF4:Yb/Er nano-rods was ~11.2% (fig. S54).As a living free-radical polymerization tech-

nique, ATRP affords excellent molecular weight(MW) control (20), enabling the precise design ofBBCPswith a tunableMWand narrowMWdistri-bution for each constituent block (table S2 to S10).Consequently, the diameter of 1D plain nanorodsis dictated by the length of the hydrophilic innerblock in BBCPs, which can be regulated by tuningthe polymerization time of the different blocks dur-ing ATRP. Moreover, the solubility of 1D nanocrys-tals (organic solvent–soluble or water-soluble) isrendered by the outer blocks of the BBCP brushes,which are covalently bonded to the inner blocks.Lastly, the lengthof 1Dnanocrystals canbeadjusted

by varying the length of the macroinitiator (de-noted cellulose-Br; supplementary text, section I).To obtain a specific length of cellulose-Br

macroinitiator, natural cellulose modified with2-bromoisobutyryl bromide in a mixed solventof ionic liquid, anhydrous 1-methyl-2-pyrrolidione(NMP), and DMF was purified by fractional pre-cipitation (figs. S1 to S3; table S1; and supplemen-tary text, section I). Taking noble metallic Aunanorods as an example, facile control over thenanorod length and diameter was achieved bydeliberately tuning the length of the cellulose-Brmacroinitiator and the MW of the PAA blocks,respectively, in cellulose-g-(PAA-b-PS) (Fig. 2B).As theMWof cellulose-Br increased from 11.2 ×103 to 79.6 × 103 g/mol, the length of the Au nano-rods increased from 51 ± 4 to 414 ± 39 nm. Byincreasing theMWof the PAA block from 5.2 × 103

to 11.2 × 103 g/mol, the diameter of the Au nano-rods increased from 10.4 ± 0.6 to 21.2 ± 1.5 nm.Conceptually, because many appropriate pre-

cursors are amenable to the cylindrical unimolecularnanoreactor strategy, a variety of uniformnano-rods can be created. Figure 3 shows noble metallicAu (figs. S12, S55, and S66) and Pt (fig. S13), fer-roelectric BaTiO3 (fig. S18), upconversion NaYF4:Yb/Er (figs. S14, S15, and S58) and NaYF4:Yb/Tm(figs. S16, S17, and S59), semiconducting CdSe(figs. S19 and S57), thermoelectric PbTe (figs. S20and S67), andmagnetic Fe3O4 (fig. S21) nanorods

synthesized by our cylindrical cellulose-g-(PAA-b-PS) nanoreactor approach. The possible mech-anisms for the growth of these plain nanorodsare shown in figs. S38 to S42 (supplementary text,section IV). Their crystalline lattices are shown asinsets in Fig. 3 and fig. S52, with their crystalstructures and compositions substantiated byXRD (fig. S60) and EDS measurements (fig. S63)(supplementary text, section IX). Because thenanorods are cappedwith PS chains that preventtheir aggregation (figs. S48 to S50), they arehomogeneously soluble in awide range of organicsolvents (e.g, toluene and chloroform) (fig. S53).The excess precursors that are present outsidethe cylindrical BBCP nanoreactor can easily formlarge, irregular, inorganic materials because ofthe lack of surface capping by PS chains, and thusthey readily precipitate from organic solventswhen subjected to low-speed centrifugation. Al-ternatively, the upper solution containing the 1Dnanocrystals can also be directly retrieved. Ournanoreactor strategy is effective in producingrelatively pure 1D nanocrystals (figs. S51 and S70and supplementary text, section V).A double-hydrophilic cylindrical cellulose-g-

(PAA-b-PEG) BBCP was synthesized by a combi-nation of ATRP and a click reaction (fig. S9; tableS3; and supplementary text, section II) [PEG,poly(ethylene glycol)]. Using this as a nanoreactor,we created a series of water-soluble PEG-capped

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Fig. 1. Synthetic strategies for 1D nanocrystals, using amphiphiliccylindrical BBCPs as nanoreactors. (A) Plain nanorods templated bycellulose-g-(PAA-b-PS). St, styrene; tBA, tert-butyl acrylate. (B) Core-shellnanorods templated by cellulose-g-(P4VP-b-PtBA-b-PS). (C) Nanotubestemplated by cellulose-g-(PS-b-PAA-b-PS).

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Fig. 2. Formation of plain nanorods. (A) TEM images of upconversion NaYF4:Yb/Ernanorods templated by cellulose-g-(PAA-b-PS) (sample 2A in table S2).The lower rightpanel is a HRTEM image showing crystal lattices. The insets are digital images ofNaYF4:Yb/Er nanorods in toluene (lower left panel) and dry state (upper right panel)before (left) and after (right) exposure to a 980-nm near-infrared laser. (B) The dimensional tunability of 1DAu nanorods is shown as an example.The upper panelshows the dependence of the length Lof Au nanorods on themolecular weightMn of cellulose-Brmacroinitiator (table S1).The lower panel shows the dependenceof the diameter D of Au nanorods (marked by arrows in the insets) on the molecular weight of PAA block in BBCP (table S2).

Fig. 3. TEM images of a variety of plain nano-rods templated by cellulose-g-(PAA-b-PS). Thedimensions of these nanorods are as follows: noblemetallic Au, L = 206 ± 19 nm and D = 21.2 ± 1.5 nmfrom sample 3B; noble metallic Pt, L = 48 ± 5 nmandD = 10.2 ± 0.6 nm from sample 1A; ferroelectricBaTiO3, L = 101 ± 8 nm and D = 10.6 ± 0.8 nm fromsample 2A; upconversion NaYF4:Yb/Er (green-emitting), L = 99 ± 10 nm and D = 9.6 ± 0.4 nmfromsample 2A; upconversionNaYF4:Yb/Tm (blue-emitting), L = 103 ± 7 nm and D = 10.4 ± 0.5 nmfrom sample 2A; semiconducting CdSe, L = 98 ±9 nm and D = 10.1 ± 0.7 nm from sample 2A;thermoelectric PbTe, L= 102 ± 10 nmandD=9.9 ±0.6 nm fromsample 2A;magnetic Fe3O4, L=203 ±16 nm and D = 10.2 ± 0.8 nm from sample 3A andL = 916 ± 87 nm and D =10.3 ± 0.5 nm fromsample 5A. Insets at the bottom of each panel areHRTEM images showing the crystal lattice of thesample. The upper insets in the middle-left andcenter panels are digital images of green-emittingNaYF4:Yb/Er and blue-emitting NaYF4:Yb/Tm nano-rods, respectively, under near-infrared laser illumi-nation (980 nm at 2 W). The upper insets in thebottom right panel are digital images demonstratingthe magnetic properties of Fe3O4 nanorods as theywere deposited on the wall of vial (right) by a mag-netic bar. Further details about the samples are givenin table S2.

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plain Au (figs. S22, S23, and S56), NaYF4:Yb/Er(fig. S24), and Fe3O4 (fig. S25) nanorods (supple-mentary text, section III). These water-soluble 1Dnanocrystals are pertinent to a number of sci-entific areas, including self-assembly, bioimaging,and biosensors.Our cylindrical BBCP nanoreactor strategy

also affords a platform to synthesize high-qualitycore-shell nanorods composed of two differentmaterials that have large lattice mismatches. Forthe synthesis of high-quality core-shell nano-particles, a moderate lattice mismatch (<2%) be-tween two dissimilar materials is necessary forsuccessful epitaxial growth (21). This greatly limitsthe core and shell material choices for sequentialepitaxial growth (22). Furthermore, in comparisonwith core-shell nanoparticles, the effectivemethodsto produce core-shell nanorods are few and limitedin scope (23).The creation of core-shell nanorods with con-

trolled dimensions (core diameter, shell thickness,and length), compositions, and solubility is enabledby using a class of cylindrical BBCPs comprisingdensely grafted amphiphilic triblock copolymerside chains. Specifically, cellulose-g-(P4VP-b-PtBA-b-PS) and cellulose-g-(P4VP-b-PtBA-b-PEG) canserve as organic-soluble and water-soluble nano-reactors, respectively (supplementary text, sec-tion III) [PV4P, poly(4-vinylpyridine)]. Similarto the synthesis of plain nanorods, in polar DMFsolvent, precursors are selectively partitioned inthe corresponding template compartments of thetriblock copolymer–containing BBCPs by meansof a favorable coordination interaction betweenthe functional groups of the template blocks andthe metal moieties of the precursors. In succes-sion, the core and shell components of the nano-rod can be grown.

We describe the synthesis of nanorods with anoble metallic Au core and amagnetic Fe3O4 shellas an example to demonstrate the effectiveness ofcylindrical cellulose-g-(P4VP-b-PtBA-b-PS) BBCPs(upper right panel in Fig. 1B) as nanoreactors inproducingorganic solvent–soluble core-shell nano-rods (supplementary text, section III). The Au-core nanorod with L = 103 ± 7 nm andD = 10.5 ±0.6 nm (Fig. 4A and fig. S68) was synthesized inDMF through preferential partitioning of Au pre-cursors in the compartment of the inner P4VPblocks, whose pyridyl groups imparted and coor-dinated with a large population of precursors(central panel in Fig. 1B). The possible formationmechanism is illustrated in fig. S43. Subsequently,the PtBA blocks of the PtBA-b-PS capping on thesurface of the Au-core nanorods were hydrolyzedinto PAA blocks (supplementary text, sectionIII), thus templating the formation of the Fe3O4

shell in DMF in a similar fashion to that of theAu core (fig. S44). The resulting Au-Fe3O4 core-shell nanorods capped by PS exhibited uniformdimensions. The HRTEM image clearly showsthe dark crystalline Au core surrounded by a shellof relatively lighter Fe3O4 (4.6 ± 0.4 nm thick) (Fig.4B). The XRD and EDS measurements furtherverified the crystal structure and composition ofFe3O4 and Au, respectively (figs. S61 and S64). Itis important to note that despite a lattice mis-match of more than 50% between Fe3O4 and Au(24), Au-Fe3O4 core-shell nanorods were success-fully created by capitalizing on the cylindricalcellulose-g-(P4VP-b-PtBA-b-PS) BBCP nanoreactor.Many other material combinations can also beprepared to produce organic solvent–soluble core-shell nanorods (e.g., magnetic-metallic Fe3O4-Au,shown in fig. S26, and metallic-semiconductingAu-TiO2, shown in figs. S27, S28, and S45).

Similarly, the use of the cylindrical cellulose-g-(P4VP-b-PtBA-b-PEG) BBCP (supplementary text,section III; upper right panel in fig. S10) as ananoreactor yieldedwater-soluble core-shell nano-rods (lower left panel in fig. S10), such as metallic-semiconducting Au-TiO2 (figs. S29 and S30) andmetallic-upconversion Au-NaYF4:Yb/Er (fig. S31),eachwith hydrophilic PEGblocks directly tetheredto their surface (table S5 and supplementary text,section III). Likewise, the crystal structures andcompositions of these nanorods were confirmedby XRD and EDSmeasurements (supplementarytext, section IX).The core diameter and shell thickness of

nanorods can be precisely tuned by varying theMW of the inner P4VP block and the inter-mediate PtBA block. These are controlled bymediating the sequential ATRP polymerizationtimes. A uniform nanorod length is attained bycontrolling the length of the cellulose-Br macro-initiator through fractional precipitation. Becausethe core and shell materials can be grown in-dependently in their respective templates, thelattice structure of the synthesized shell materialcan be completely independent of the core mate-rial. This cylindrical BBCP nanoreactor strategycan virtually eliminate the restriction on latticematching requirements (21). Thus, our cylindricalBBCP composed of amphiphilic triblock copo-lymer arms can be used to create a new class ofexotic core-shell nanorods that would otherwisebe challenging to obtain. Through the precisetailoring of various core and shell combinations,it is possible to explore potentially new coupledsize- and shape-dependent properties.The amphiphilic cylindrical BBCPnanoreactor

strategy can also be used to synthesize uniformnanotubes (hollow nanorods) by selectively

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Fig. 4. TEM and digital images of Au-Fe3O4 core-shell nanorods and Au nanotubes templated by cellulose-g-(P4VP-b-PtBA-b-PS) and cellulose-g-(PS-b-PAA-b-PS), respectively. (A) TEM images of Au-core nanorods(L = 103 ± 7 nm,D = 10.5 ± 0.6 nm). A digital image of Au-core nanorods in toluene (top) and aHRTEM image of a Au

nanorod (bottom) are shown as insets. (B) TEM images of Au-Fe3O4 nanorods (Fe3O4 shell thickness t = 4.6 ± 0.4 nm) (sample 2B; table S4).The HRTEM image(bottom left) shows the crystal lattice of the Au core and Fe3O4 shell (white dashed lines for guidance).The bottom right panel shows digital images demonstratingthemagnetic properties of Au-Fe3O4 nanorods. (C) TEM images of Au nanotubes at different magnifications (L = 103 ± 12 nm, t = 5.1 ± 0.5 nm, hollow interiorD =5.3 ± 0.4 nm) (sample 2A; table S6).The inset is a digital image of Au nanotubes in toluene.

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restricting the appropriate precursors to theintermediate B block of an A-b-B-b-A BBCP tri-block copolymer nanoreactor. The inside and out-side surfaces of the nanotubes are capped by innerandouterAblocks. As an example, organic solvent–soluble Au nanotubes (table S6 and supplemen-tary text, section III) were synthesized by usingamphiphilic cellulose-g-(PS-b-PAA-b-PS) as anano-reactor (upper right panel in Fig. 1C and fig. S69).The Au precursors were sequestered in the com-partment containing the intermediate PAA blocksand ultimately formed PS-capped Au nanotubes(lower left panel in Fig. 1C). In Fig. 4C, the centerof the nanotubes appears brighter, signifyingthat they are hollow. The HRTEM image (lowerright panel in Fig. 4C) and XRD pattern (fig. S62)suggest that the nanotubes are highly crystalline.Moreover, EDSmeasurements further corroboratethe successful formation of Au nanotubes (fig.S65). The diameter of the hollow interior and thethickness of the nanotube can be controlled bytailoring the MWs of the inner PS block andintermediate PtBA block during sequential ATRP.Thus, an assortment of nanotubes with differentsizes and compositions canbe produced, includingupconversion NaYF4:Yb/Er nanotubes (figs. S32and S33) and semiconducting TiO2 nanotubes(figs. S34 and S46). Despite the uniformdiameterand thickness, there was a distribution of Au nano-tube lengths (Fig. 4C) because of the differentlengths of the individual cellulose-Br macro-initiators used to prepare the cellulose-g-(PS-b-PAA-b-PS) nanoreactors. However, cellulose-Brmacroinitiators with uniform lengths can berealized by fractional precipitation. Likewise, byusing cellulose-g-(PS-b-PAA-b-PEG) nanoreactors(fig. S11), water-soluble nanotubes (e.g., Au, TiO2,andNaYF4:Yb/Er nanotubes in figs. S35, S36, andS37, respectively) can also be synthesized (table S7and supplementary text, section III).All of the 1D nanocrystals that we produced

(Figs. 2 to 4) had round ends. This is not sur-prising, given that each cellulose backbone washeavily grafted with diblock or triblock copoly-mer arms. These arms can stretch out at thetwo ends of the cylindrical BBCPs because of theavailable space there. Moreover, the two ends ofthe cellulose backbone have two hydroxyl groups,which allows for the growth of a diblock ortriblock copolymer arm at each end. Together,the brushes on the ends of the cylindrical BBCPshave a hemispherical chain conformation. Thisleads to the formation of hemisphere-shapednanocrystals situated at both ends of the 1Dnanocrystals. The reaction temperature for thesynthesis of nanorodswas lower than the degrada-tion temperature Td of nanoreactors measured byTGA [e.g., Td = 210°C for cellulose-g-(PAA-b-PS)](fig. S54). Thus, the polymer templates are likelyencased by 1D nanocrystals.Wehave developed a general and robust strategy

for the synthesis of a variety of 1D nanocrystalsin a way that allows high-level control over di-mension, anisotropy, composition, surface chem-istry, and architecture. Central to this effectivestrategy is the rational design and synthesis offunctional BBCPs—composed of a cellulose back-

bone densely grafted with diblock or triblockcopolymers of precisely tunable lengths—thatserve as nanoreactors. All of these 1D nanocrystalscan be used as building blocks in the bottom-upassembly of nanostructuredmaterials and deviceswithdesirable characteristics (enabledby theprop-erties of individual nanocrystals and their properspatial arrangement) for use in optics, electronics,optoelectronics, magnetic technologies, sensors,and catalysis, among other applications. They canalso serve as model systems for fundamental re-search in self-assembly, phase behavior, and crys-tallization kinetics of nanocrystals (25).

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105, 1025–1102 (2005).

ACKNOWLEDGMENTS

We gratefully acknowledge funding support from the Air ForceOffice of Scientific Research (grant FA9550-16-1-0187). Theauthors also thank C. Feng for nuclear magnetic resonance andTGA measurements; B. Li for TEM measurements; X. Xin, D. Zheng,and M. Wang for EDS measurements; J. Iocozzia for comments;and Y. Yang for graphic assistance. Z.L. and X.P. conceived anddesigned the experiments. X.P., Y.H., and J.J. performed theexperiments. Z.L., X.P., Y.H., and J.J. analyzed the data. Z.L.and X.P. wrote the paper. All the authors discussed the resultsand commented on the manuscript. The authors declare nocompeting financial interests.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/353/6305/1268/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S71Tables S1 to S10References (26–42)

7 November 2015; accepted 3 August 201610.1126/science.aad8279

MARINE MICROBIOME

Decoupling function and taxonomy inthe global ocean microbiomeStilianos Louca,1,2,5* Laura Wegener Parfrey,1,3,4 Michael Doebeli1,4,5

Microbial metabolism powers biogeochemical cycling in Earth’s ecosystems.The taxonomiccomposition of microbial communities varies substantially between environments, but theecological causes of this variation remain largely unknown.We analyzed taxonomic andfunctional community profiles to determine the factors that shape marine bacterial andarchaeal communities across the global ocean. By classifying >30,000marinemicroorganismsinto metabolic functional groups, we were able to disentangle functional from taxonomiccommunity variation.We find that environmental conditions strongly influence the distributionof functional groups in marine microbial communities by shaping metabolic niches, but onlyweakly influence taxonomic composition within individual functional groups. Hence, functionalstructure and composition within functional groups constitute complementary and roughlyindependent “axes of variation” shaped by markedly different processes.

Microbial communities drive global biogeo-chemical cycling (1). Bacteria and archaea,for example, strongly influence marinecarbon, nitrogen, and sulfur fluxes, therebymodulating global ocean productivity and

climate (2, 3). Elucidating the processes that shapemicrobial communities over space and time is im-portant for predicting how biogeochemical cycleswill changewithchangingenvironmental conditions.

Taxonomicmicrobial community profiling canreveal intriguing, but often unexplained, variation

1272 16 SEPTEMBER 2016 • VOL 353 ISSUE 6305 sciencemag.org SCIENCE

1Biodiversity Research Centre, University of British Columbia,Canada. 2Institute of Applied Mathematics, University ofBritish Columbia, Canada. 3Department of Botany, Universityof British Columbia, Canada. 4Department of Zoology,University of British Columbia, Canada. 5Department ofMathematics, University of British Columbia, Canada.*Corresponding author. Email: louca@zoology.ubc.ca

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1D nanocrystals with precisely controlled dimensions, compositions, and architecturesXinchang Pang, Yanjie He, Jaehan Jung and Zhiqun Lin

DOI: 10.1126/science.aad8279 (6305), 1268-1272.353Science 

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REFERENCES

http://science.sciencemag.org/content/353/6305/1268#BIBLThis article cites 42 articles, 5 of which you can access for free

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