Editorial Board

Supported by NSFC

Honorary Editor General ZHOU GuangZhao (Zhou Guang Zhao)

Editor General ZHU ZuoYan Institute of Hydrobiology, CAS, China

Editor-in-Chief LI LeMin Peking University, China

Associate Editor-in-Chief CAO Yong South China University of Technology, China TIAN ZhongQun Xiamen University, China CHEN HongYuan Nanjing University, China XUE Zi-Ling University of Tennessee, USA FENG ShouHua Jilin University, China YUAN Quan Dalian Institute of Chemical Physics, CAS, China LIN GuoQiang Shanghai Institute of Organic Chemistry, CAS, China

Members

BAO XinHe Dalian Institute of Chemical Physics, CAS, China BU XianHe Nankai University, China CHAI ZhiFang Institute of High Energy Physics, CAS, China CHAN Albert S C Hong Kong Polytechnic University, China CHEN Xian University of North Carolina-Chapel Hill, USA CHEN XiaoMing Sun Yat-Sen University, China CHEN Yi Institute of Chemistry, CAS, China CUI ZhanFeng Oxford University, UK DUAN Xue Beijing University of Chemical Technology, China

FEI WeiYang Tsinghua University, China FENG XiaoMing Sichuan University, China GAO ChangYou Zhejiang Universtiy, China GAO Song Peking University, China GUO ZiJian Nanjing University, China

HAN BuXing Institute of Chemistry, CAS, China

HE MingYuan Research Institute of Petroleum Processing, SINOPEC, China HONG MaoChun Fujian Institute of Research on the Structure of Matter, CAS, China HUANG PeiQiang Xiamen University, China HUANG Zhen Georgia State University，USA

JIANG GuiBin Research Center for Eco-Environmental Sciences, CAS, China

JIANG Long Institute of Chemistry, CAS, China

JIAO Kui Qingdao University of Science and Technology, China JU HuangXian Nanjing University, China KONG Wei Oregon State University, USA LI QianShu South China National University, China LI YaDong Tsinghua University, China

LIAN TianQuan Emory University, USA

LIANG WenPing National Natural Science Foundation of China, China LIN JianHua Peking University, China LIU GuoJun Queen’s University, Canada LIU Jun O Johns Hopkins Medicine Institute, USA LU FengCai Institute of Chemistry, CAS, China NIE ShuMing Georgia Institute of Technology and Emory University, USA PAN CaiYuan University of Science and Technology of China, China PU Lin University of Virginia, USA QIAO JinLiang SINOPEC Beijing Research Institute of Chemical Industry, China SHAO YuanHua Peking University, China SHEN ZhiQuan Zhejiang University, China SHUAI ZhiGang Tsinghua University, China SUN LiCheng Royal Institute of Technology (KTH), Sweden TANG Ben Zhong Hong Kong University of Science & Technology, China TIAN He East China University of Science & Technology, China TONG Liang Columbia University, USA TUNG ChenHo Technical Institute of Physics and Chemistry, CAS, China WAN LiJun Institute of Chemistry, CAS, China WANG MeiXiang Institute of Chemistry, CAS, China WANG ShiQing University of Akron, USA WANG ZhenGang California Institute of Technology, USA WANG ZhongLin Georgia Institute of Technology, USA WU YunDong Hong Kong University of Scence & Technology, China XIE ZuoWei Chinese University of Hong Kong, China

XIONG RenGen South East University, China XU ChunMing China University of Petroleum, China YAM Vivian Wing-Wah University of Hong Kong, China YAN DeYue Shanghai Jiao Tong University, China YANG Bai Jilin University, China YANG DongSheng University of Kentucky, USA YANG PengYuan Fudan University, China YANG WeiTao Duke University, USA YANG XueMing Dalian Institute of Chemical Physics, CAS, China YANG YuLiang Fudan University, China YAO ShouZhuo Hunan University, China YAO ZhuJun Shanghai Institute of Organic Chemistry, CAS, China YOU XiaoZeng Nanjing University, China YU LuPing University of Chicago, USA ZHANG HongJie Changchun Institute of Applied Chemistry, CAS, China ZHANG JinSong University of California, Riverside, USA ZHANG JinZhong University of California, Santa Cruz, USA ZHANG John ZengHui New York University, USA ZHANG LiHe Peking University, China ZHANG Xi Tsinghua University, China ZHANG YuKui Dalian Institute of Chemical Physics, CAS, China ZHAO XinSheng Peking University, China ZHAO YuFen Xiamen University, China ZHENG LanSun Xiamen University, China ZHOU QiLin Nankai University, China ZHU Tong Peking University, China ZHU Julian X Université de Montréal, Canada

Editorial Staff ZHU XiaoWen (Director) SONG GuanQun ZHANG XueMei

SCIENCE CHINA Chemistry

© Science China Press and Springer-Verlag Berlin Heidelberg 2012 chem.scichina.com www.springerlink.com

Contents Vol.55 No.5 May 2012

SPECIAL ISSUE: In Honor of the 80th Birthday of Professor WANG Fosong Preface

CHENG Stephen Z. D. & CAO Yong Sci China Chem, 2012, 55(5): 643–645

NEWS & COMMENTS

Professor Fosong Wang on his 80th birthday: A great scientist and a great ambassador

SAWAMOTO Mitsuo

Sci China Chem, 2012, 55(5): 647

FEATURE ARTICLES

Design and synthesis of self-healing polymers

ZHANG MingQiu & RONG MinZhi

Sci China Chem, 2012, 55(5): 648–676

New D--A dyes for efficient dye-sensitized solar cells

QU SanYin, HUA JianLi & TIAN He

Sci China Chem, 2012, 55(5): 677–697

Microstructure, morphology, crystallization and rheological behavior of impact polypropylene copolymer

SHANG-GUAN YongGang, CHEN Feng & ZHENG Qiang

Sci China Chem, 2012, 55(5): 698–712

ii

The abnormal behavior of polymers glass transition temperature increase and its mechanism

WANG Xiang, QI GuiCun, ZHANG XiaoHong, GAO JianMing, LI BingHai, SONG ZhiHai & QIAO JinLiang

Sci China Chem, 2012, 55(5): 713–717

REVIEWS

Recent advances in flexible and stretchable electronics, sensors and power sources

TOK Jeffrey B.-H. & BAO Zhenan

Sci China Chem, 2012, 55(5): 718–725

Polystyrene-based blend nanorods with gradient composition distribution

WU Hui, SU ZhaoHui, TERAYAMA Yuki & TAKAHARA Atsushi

Sci China Chem, 2012, 55(5): 726–734

Self-assembled structures of a semi-rigid polyanion in aqueous solutions and hydrogels

SUN TaoLin, WU ZiLiang & GONG JianPing

Sci China Chem, 2012, 55(5): 735–742

iii

ARTICLES

Large open-circuit voltage polymer solar cells by poly(3-hexylthiophene) with multi-adducts fullerenes

GONG Xiong, YU TianZhi, CAO Yong & HEEGER Alan J.

Sci China Chem, 2012, 55(5): 743–748

Polymer solar cells with an inverted device configuration using polyhedral oligomeric silsesquioxane-[60]fullerene dyad as a novel electron acceptor

ZHANG Wen-Bin, TU YingFeng, SUN Hao-Jan, YUE Kan, GONG Xiong & CHENG Stephen Z. D.

Sci China Chem, 2012, 55(5): 749–754

Inverted polymer solar cells with a solution-processed zinc oxide thin film as an electron collection layer

YANG TingBin, QIN DongHuan, LAN LinFeng, HUANG WenBo, GONG Xiong, PENG JunBiao & CAO Yong

Sci China Chem, 2012, 55(5): 755–759

iv

A structurally ordered thiophene-thiazole copolymer for organic thin-film transistors

CHEN DuGang, ZHAO Yan, ZHONG Cheng, YU Gui, LIU YunQi & QIN JinGui

Sci China Chem, 2012, 55(5): 760–765

Alkali metal salts doped pluronic block polymers as electron injection/transport layers for high performance polymer light-emitting diodes

ZHANG Kai, LIU ShengJian, GUAN Xing, DUAN ChunHui, ZHANG Jie, ZHONG ChengMei, WANG Lei, HUANG Fei & CAO Yong

Sci China Chem, 2012, 55(5): 766–771

Preparation and self-assembly of amphiphilic polymer with aggregation-induced emission characteristics

QIN AnJun, ZHANG Ya, HAN Ning, MEI Ju, SUN JingZhi, FAN WeiMin & TANG Ben Zhong

Sci China Chem, 2012, 55(5): 772–778

Shear and extensional rheology of entangled polymer melts: Similarities and differences

SUN Hao & WANG Shi-Qing

Sci China Chem, 2012, 55(5): 779–786

v

Energetics of dioxygen binding into graphene patches with various sizes and shapes

YUMURA Takashi, KOBAYASHI Hisayoshi & YAMABE Tokio

Sci China Chem, 2012, 55(5): 787–795

Theoretical study of current-voltage characteristics of carbon nanotube wire functionalized with hydrogen atoms

FUENO Hiroyuki, KOBAYASHI Yoshikazu & TANAKA Kazuyoshi

Sci China Chem, 2012, 55(5): 796–801

Tuning periodicity of polymer-decorated carbon nanotubes

WANG WenDa, LAIRD Eric D., LI Bing, LI LingYu & LI Christopher Y.

Sci China Chem, 2012, 55(5): 802–807

Electrical conductivities of carbon nanotube-filled polycarbonate/polyester blends

XIONG ZhuoYue, SUN Yao, WANG Li, GUO ZhaoXia & YU Jian

Sci China Chem, 2012, 55(5): 808–813

vi

Comparison of magnetic properties of DNA-cetyltrimethyl ammonium complex with those of natural DNA

KWON Young-Wan, CHOI Dong Hoon, JIN Jung-Il, LEE Chang Hoon, KOH Eui Kwan & GROTE James G.

Sci China Chem, 2012, 55(5): 814–821

TEMPO-substituted polyacrylamide for an aqueous electrolyte-typed and organic-based rechargeable device

CHIKUSHI Natsuru, YAMADA Hiroshi, OYAIZU Kenichi & NISHIDE Hiroyuki

Sci China Chem, 2012, 55(5): 822–829

Oxidative polymerization of hydroquinone using deoxycholic acid supramolecular template

ZHANG AiJuan, HE Jian, GUAN Ying, LI ZhanYong, ZHANG YongJun & ZHU Julian X.

Sci China Chem, 2012, 55(5): 830–835

Electrochemically sensitive supra-crosslink and its corresponding hydrogel

DU Ping, CHEN GuoSong & JIANG Ming

Sci China Chem, 2012, 55(5): 836–843

vii

Exploration of structure and mechanism of insoluble gels formed in microwave-assisted Suzuki coupling for poly(9,9-dihexylfluorene)s

ZHANG WenSi, LU Ping, WANG ZhiMing & MA YuGuang

Sci China Chem, 2012, 55(5): 844–849

Improvement of the physical properties of poly(methyl methacrylate) by copolymerization with N-pentafluorophenyl maleimide; zero-orientational and photoelastic birefringence polymers with high glass transition temperatures

TAGAYA Akihiro, LOU LiPing, IDE Yoko, KOIKE Yasuhiro & OKAMOTO Yoshiyuki

Sci China Chem, 2012, 55(5): 850–853

Chemical-physical aspects of formation and evolution of phase structure in multi-polymers: Intensity fluctuation, phase structure and its fractal characteristics in blends of isotactic polypropylene with poly(cis-1,4-butadiene) rubber

MA GuiQiu, YANG YuPing, HUANG DingHai & SHENG Jing

Sci China Chem, 2012, 55(5): 854–864

SCIENCE CHINA Chemistry

© Science China Press and Springer-Verlag Berlin Heidelberg 2012 chem.scichina.com www.springerlink.com

*Corresponding author (email: Chrisli@drexel.edu)

• ARTICLES • May 2012 Vol.55 No.5: 802–807

· SPECIAL ISSUE · In Honor of the 80th Birthday of Professor WANG Fosong doi: 10.1007/s11426-012-4502-4

Tuning periodicity of polymer-decorated carbon nanotubes

WANG WenDa, LAIRD Eric D., LI Bing, LI LingYu & LI Christopher Y.*

A. J. Drexel Nanotechnology Institute and Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104, USA

Received October 1, 2011; accepted November 23, 2011; published online February 2, 2012

Carbon nanotube (CNT) is one of the most extensively investigated nanomaterials. Patterning soft matter such as liquid crys-tals and polymers on CNTs could potentially enable various applications for CNTs. We have demonstrated that controlled polymer crystallization using CNTs as the 1D nucleation sites can lead to periodically functionalized CNTs. Here we show that selected crystalline block copolymers can be periodically decorated along CNTs. This facile technique opens a gateway to pe-riodic patterning on 1-D nanomaterials.

polymer crystallization, carbon nanotube, block copolymers

1 Introduction

Functionalization of carbon nanotubes (CNTs) is of great interest from both scientific and technological viewpoints [1–3]. Periodically functionalized CNTs can directly lead to controlled two-dimensional or three-dimensional CNT su-prastructures, which is an essential step toward building future CNT-based nanodevices. Very few reports have ad-dressed periodic functionalization/patterning on CNTs. Czerw et al. demonstrated regular organization of poly (propionylethylenimine-co-ethylenimine) on CNTs using Scanning Tunneling Microscopy (STM) [4]. Single-stranded DNAs have been bound to CNTs, resulting in periodic heli-cal wrapping on the surface of CNTs [5, 6]. Surfactants such as sodium dodecyl sulfate (SDS) have been found to form uniform patterns on CNTs [7]. On the other hand, CNT-induced polymer crystallization is studied in polymer CNT nanocomposites (PCNs) formed by CNTs and semi-crystalline polymers such as iPP [8–12], PE [13], polyvinyl alcohol (PVA) [14], polyacrylonitrile (PAN) [15–17], ther-moplastic polyimide [18], conjugated organic polymer [19], as well as thermoplastic elastomers such as polyurethane

[20–22]. Polymer crystallization has been recently used to probe

polymer/nanoparticle interface [23–32]. In order to clearly reveal the CNT/polymer interface and periodically pattern crystalline polymers on CNTs, we proposed to use a con-trolled solution crystallization method. Polymer single crys-tal-functionalized CNTs were recently observed [23, 33–40]. This novel technique is a generic method for CNT and nan-ofiber functionalization [41, 42]. It can be used for a variety of CNTs, including single-walled (SWNT), multi-walled (MWNT) and vapor grown carbon nanofibers (CNF). For-mation mechanism of this unique structure was attributed to “size-dependent soft epitaxy”. Two main factors affected the polymer chain orientation on CNT during crystal growth: epitaxy and geometry confinement. As the diameter of the CNT is comparable to the radius of gyration of a polymer chain, its highly curved surface leads to strong geometric confinement and polymer chains are forced to align parallel to the CNT surface upon crystallization, regardless of the CNT chirality. As the diameter increases to ~100–300 nm, the geometric confinement effect became weakened and epitaxy dictated the polymer lamellar growth.

We have also demonstrated that the periodic structure is largely due to density fluctuation of polymer concentration along the CNT surface during the crystallization process;

Wang WD, et al. Sci China Chem May (2012) Vol.55 No.5 803

the pattern therefore is not quite regular. To this end, using semicrystalline block copolymers (BCP) could lead to uni-form patterns [43, 44]. The research work involving both BCP and CNTs has been reported by a few groups [45–50]. For example, Taton and his coworkers used BCP polysty-rene-block-poly(acrylic acid) (PS-b-PAA) to form micelles in H2O/ dimethylformamide solution [47]. SWNT was en-capsulated in core of the micelles made of PS while PAA can be further cross-linked to form a solid structure. The similar concept was adopted later on by Park et al. [49], and Agarwal et al. [46]. Most recently, we demonstrated that low molecular weight polyethylene-b-poly (ethylene oxide) (PE-b-PEO) BCP could be patterned onto CNT surface [39]. Herein we report that polymer crystallization induced phase separation holds the key to this regular pattern formation. This unique hybrid structure is promising for a variety of nanoelectronic and biomedical applications.

2 Experimental

2.1 Materials

Purified HiPco SWNTs were purchased from Carbon Nan-otechnologies Inc. 1,2-Dichlorobenzene (DCB), pentyl ace-tate, thioglycolic acid, sulfuric acid (98%), isopropyl ether, dichloromethane, toluene and chloroform were purchased from Sigma-Aldrich and used as received. PE-b-PEO (mo-lecular weight 1,400 g/mol, 50 wt% PE) was purchased from Sigma-Aldrich and was fractionated before usage. Polybutadiene (1,4 rich)-b-poly (ethylene oxide) (PB-b-PEO) (molecular weight 930–1020 g/mol) was purchased from Polymer Source Inc. and used as received. PE-b-SBR block copolymer samples were kindly provided by Bridgstonetire Co. PE block synthesized by hydrogenation of polybutadi-ene (PB) has average molecular weight (MW) of 25,200, polydispersity index (PDI) of 1.14 and SBR has MW of 100,220 and PDI of 1.25. The total hydrogenation percent-age is 99.3%.

2.2 Instruments

The Branso Ultrasonic Cleaner was used for sonication. Spincoating was performed on the Specialty Coating Sys-tems Spin Coater-G3P12. The Fisher Scientific Centrifuge Marathon 21000 was used for centrifugation. TEM experi-ments were conducted on the JEOL 2000FX TEM with an accelerating voltage of 120 kV. The PDI of PE-b-PEO was characterized by gel permeation chromatography (GPC) at 40 °C using tetrahydrofuran as the eluent at a flow rate of 1.0 mL/min. Data were collected by the Refractive Index Detector 2414 and analyzed using the software provided by Waters. The calibration curve was constructed with nar-rowly distributed PEO standards. Proton nuclear magnetic resonance (1H NMR) was measured on the Unityinova 500 MHz NMR Spectrometer. The Fourier Transform Infrared

(FTIR) spectra were obtained on the Varian Excalibur FTS-3000. Vacuum evaporation of carbon was conducted on a Polaron Range E6300 Vacuum Evaporator.

2.3 Fractionation of PE-b-PEO

10 g of PE-b-PEO was dissolved in 50 mL of dichloro-methane. 100 mL of isopropyl ether was added to the solu-tion subsequently. The mixture was then placed in a vacuum chamber to gradually remove the solvents. The BCPs with the highest PE percentage precipitated out first. The precip-itated BCP was collected and labeled as fraction 1 to 6 in a time order. Fraction 4 was chosen to be used in this research. The GPC spectrum shows that the PDI of the fractionated BCP is 1.15. From the end-group analysis using 1H NMR, the molecular weight is 1700 g/mol and the PE block is 50 wt%.

2.4 Thin film crystallization of BCP on SWNTs

0.02 mg of SWNTs was dissolved in 1.0 g of DCB by 1 h sonication. The SWNT/ DCB solution was dropcast on the carbon-coated nickel grids and dried at ambient temperature. BCP/chloroform solution with various concentrations was spincoated on the SWNT-loaded grids at 3000 r/min for 30 s. The samples were stained by ruthenium tetroxide (RuO4) prior to the TEM observation.

2.5 Solution crystallization

For polymer solution crystallization, DCB was used as sol-vent. 0.1–0.5 mg PE-b-SBR was dissolved in 4 g DCB at 120 °C. 0.1 mg SWNT and 1 g DCB solution was sonicated for 2–3 h at 45 C and then added to PE/ DCB solution. The mixture was then quenched to the preset crystallization temperature (Tc = 88 °C). The crystallization time was con-trolled to be 0.5–3 h. Sample was isothermally filtered after crystallization to remove the uncrystallized materials.

3 Results and discussion

3.1 Homopolymer decorated CNTs

Figure 1 shows an unshadowed TEM image of PE single crystal decorated SWNT. Edge-on PE crystals can be clear-ly seen from the image. Selective area electron diffraction (ED) pattern from the circled area is shown in Figure 1(b). While it is relatively weak, a pair of (002) diffraction spots can be seen and the orientation is parallel to the lamellar normal (CNT axis). This confirms that PE crystals are formed by CNT-induced PE crystallization and the polymer chains are parallel to the CNT axis. Figure 1(c) shows the schematic representation of the unique hybrid structure. This fibril-linked-disc structure is similar to the classic “shish-kebab” polymer crystals formed under shear field, as

804 Wang WD, et al. Sci China Chem May (2012) Vol.55 No.5

first observed in the 1960s by Pennings [51, 52]. A shish- kebab polymer crystal usually consists of a central fibril (shish) and disc-shaped folded-chain lamellae (kebab) ori-ented perpendicularly to the shish. Since the morphology is similar to the classical polymer shish kebabs, nano hybrid shish kebab (NHSK) is used to describe the structure. High resolution TEM (HRTEM) was used to reveal the fine structure on the surface of SWNTs. Figure 2 shows a HRTEM image of SWNT/PE NHSK structure. At the PE kebab vicinity area (~2–5 nm from PE kebab) there are some polymer-like coatings on SWNT surface possibly due to the dangling chains or chain ends extended from PE sin-gle crystal kebab. Note that in this case, there are bundles of SWNTs, instead of individual SWNTs, that form the shish structure. This is because that before PE crystallization, SWNTs are not completely “dissolved” so that these bun-dled SWNTs are wrapped by PE lamellar crystals.

3.2 Thin film crystallization of BCP on SWNTs

Thin film crystallization was first used to explore the feasi-bility of CNT-induced BCP crystallization. A SWNT/DCB solution was dropcast on a carbon-coated nickel grid and dried at ambient temperature. The fractionated PE-b-PEO was dissolved in chloroform and the solution was then spincoated onto the SWNT-loaded grid. Figure 3 shows a

Figure 1 TEM micrograph of SWNTs periodically patterned with PE lamellae crystals produced by crystallization of PE on SWNTs at 88 °C in DCB (a); (b) the corresponding ED pattern; (c) the schematics of a NHSK.

Figure 2 HRTEM micrograph of PE decorated SWNTs.

Figure 3 TEM image of PE-b-PEO decorated SWNTs.

TEM image of the resultant BCP/SWNT hybrid. Note that the sample is stained with RuO4 to enhance the contrast. In the image there are numerous elongated “worm-like” struc-tures with dark and bright stripes. The average length is ~1 m and the width is ~50 nm. The dark regions are PEO, while the bright ones are PE blocks because PEO was selec-tively stained by RuO4. The consistent orientations of the adjacent stripes and the aspect ratio of this unique worm-like morphology indicate that the axis of the under-neath SWNT is perpendicular to the stripes, as shown in Figure 1(b).

Observing this regular pattern on CNTs at ~12 nm scale is intriguing and the formation of this unique structure is related to the interplay between BCP phase separation and CNT-induced polymer crystallization. BCPs are known to be able to phase separate into ordered microstructures at ~10–100 nm scale [53–55]. As they are dissolved in sol-vents, BCPs can be considered as macromolecular surfac-tants [47, 56]. In a CNT/BCP system, if one segment of the BCP is crystalline and is able to form single crystals on CNTs, the BCP phase separation and the CNT-induced crystallization should affect each other. Depending on the BCP/CNT/solvent interaction parameters, a few scenarios are possible: (1) BCPs form micelles (or other aggregates), which separate from CNTs; (2) BCPs form micelles wrap-ping around CNTs; and (3) one segment of the BCP crystal-lizes on CNTs, leading to the CNT-induced BCP phase sep-aration. The morphology of the BCP/SWNT hybrid in Figure 2 clearly indicates that the phase separation of PE-b-PEO is directed by the underneath SWNTs, suggesting that scenario 3 is the dominant physical process in the present system. In order to demonstrate the role of PE crystallization in the formation of the present hybrid structures, we further con-ducted two control experiments. In the first control experi-ment, PE-b-PEO was replaced with PB-b-PEO. In the se-cond one, a thin layer of amorphous carbon was deposited onto the SWNTs prior to spincoating. In both cases, alter-nating BCP patterns were not observed on the SWNTs. These control experiments clearly demonstrated that CNT-induced PE crystallization was critical to the for-mation of the alternating patterns on the CNTs. In the present

Wang WD, et al. Sci China Chem May (2012) Vol.55 No.5 805

BCP/SWNT hybrids, upon crystallization, PE chains aligned parallel to the SWNT axis forming the bright stripes. The observed alternating stripes are thus perpendicular to the SWNT axis. Compared with the crystal patterns formed in the CNT-induced homopolymer crystallization, the present alternating pattern formed by the BCP is far more uniform. In Figure 3, the period of the alternating pattern is 11.9 ± 0.9 nm. The width of the bright stripes along the CNT axes is 5.9 ± 0.7 nm. Comparing this number with the extended chain length of the PE block suggests that each PE domain is made of one layer of interdigitated extended PE chains.

3.3 Crystallization of PE-b-SBR on SWNTs

PE-b-SBR was also used to crystallize onto SWNTs. De-tailed information regarding PE-b-SBR can be found in the experimental section. Solution crystallization was used and DCB was the model solvent. Figure 4 shows TEM images of PE-b-SBR/SWNT nanostructure. Samples in Figure 4(a) was shadowed with platinum/palladium alloy wire (80:20, 0.2 mm) to enhance the contrast. The red arrow in Figure 4(a) indicates the shadow direction. It can be seen that there are lamellar-like objects on the surface of SWNT. These objects are arranged in an orthogonal orientation with re-spect to the tube axis. These lamellar-like objects are PE-b-SBR single crystals grown in DCB solution and they seem to be rounded in shape.

The lateral size of these crystals is ~25 nm and the dis-tance between adjacent crystals is ~25–30 nm. Although shadow greatly enhanced the contrast of image, the sample appears “fatter” than its true thickness. Staining was also a widely used technique to reveal the fine structure of poly-mer and biological specimen. RuO4 was used to stain the sample. Figure 4(b) shows a TEM image of stained PE-b-SBR functionalized SWNT sample. TEM grid con-taining the sample was stained in RuO4 vapor for 15 min before imaging. It is clear that the PE-b-SBR crystals appear much thinner than those in shadowed image. The darker strips indicated by blue arrows in Figure 4(b) are PE block. There are some appealingly lighter and foggy materials

Figure 4 TEM images of PE-b-SBR functionalized SWNTs produced by crystallization of PE-b-SBR on SWNTs at 88 °C in DCB for 0.5 h. (a) TEM image of a Pt/Pd shadowed sample; (b) TEM image of a RuO4 stained sample.

which wrap on SWNT surface in between PE strips. These are loosely packed amorphous SBR block.

On the basis of the above observations, we propose a growth mechanism for the formation of the BCP-decorated SWNTs. During spincoating, the BCP molecules randomly adsorb onto the SWNT surface due to the favorable interac-tion between PE segments and SWNTs, leading to hetero-geneous nucleation. After a stable nucleus forms, the PE crystal starts to grow following the soft epitaxy mechanism [23]. In the solution crystallization case, PE crystallizes into lamellar single crystal in solution and SBR blocks are ex-cluded out of the order structure as defects. So SBR dangles either on the top or bottom of the PE lamellar in solution state. Upon solvent evaporation, SBR blocks adhere on SWNT surface because of reduced surface energy. Figure 5 shows a schematic representation of BCP decorated SWNTs.

Figure 5 Schematic illustration of PE-b-SBR functionalized SWNT structure.

4 Conclusions

We have produced nanoscale alternating patterns of BCP along SWNTs. Both PE-b-PEO and PE-b-SBR have been used to form regular and periodic patterns on SWNTs. The periodicity of the patterns was ~12–30 nm along the SWNT axis. The formation mechanism was attributed to the inter-play of CNT-induced PE crystallization and the BCP phase separation. The reported work demonstrated a facile method to achieve periodic patterning on SWNTs, a key step to-wards using 1-D nanomaterials for the nanodevice applica-tions.

This work was supported by the National Natural Science Foundation of China (DMR-0804838).

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