取向的自组装聚苯胺纳米线阵列中新型制备方法检测方案

ADVANCEDFUNCTIONALMATERIALS ADVANCEDFUNCTIONALMATERIALSH. Qiu et al./Oriented Self-Assembled Polyaniline Nanowire Arrays Oriented Growth of Self-Assembled Polyaniline Nanowire ArraysUsing a Novel Method** By Hongjin Qiu， Jin Zhai， Shuhong Li， Lei Jiang，* and Meixiang Wan* A novel method for fabrication of highly oriented polyaniline (PANI) nanowires without removal of the template was devel-oped by combining self-assembly and template synthesis techniques. By using a self-assembly process under inhibition condi-tions， oriented arrays of PANI nanowires growing out of the nanoporous template were obtained， with nanowire diametersranging from 110 to 190 nm and lengths of several micrometers. The lengths of these wires can be roughly controlled by the po-lymerization time. Nanostructure materials， especially one-dimensional (1D)nanostructures， including inorganic materials (carbon， metals，ceramics， glasses) and organic materials (biomolecules， poly-mers)， 1.2 have potential applications as electrical and opticalmaterials.3 Conducting polymer nanotubes have potentialapplications in the fabrication of many kinds of electronic de-vices，4 such as batteries， capacitors， and light-emitting diodes.Micro- and nanotubes of polyaniline and polypyrrole havebeen reported by several groups. s-9 Most of this work was car-ried out using microporous polymeric filtration membraneswith a wide range of pore diameters and pore densities astemplates. Basically， template-directed synthesis[10-12 and self-assembly growth are two typical methods for preparing 1Dtubes and fibers. Martin and co-workers 13 synthesized nano-tubes/-wires of conducting polymers using polycarbonate andalumina membranes as templates. Self-assembled nanotubes/-fibers have been reported in the literature5，6] as well. Thesetwo methods have both merits and limitations. By using thetemplate-directed synthesis method， unique and ordered struc-tures can be built directly， but post-processing is required inorder to remove the template. On the other hand， a myriad ofnanoscale morphologies can be constructed through self-as-sembly， but controlling the orientation and size (e.g.， diameter)is difficult.Recently， Liu and co-workers 14] used direct electro-chemical synthesis and fabricated uniform and oriented poly-aniline (PANI) nanowires on various substrates without using asupport template by controlling the current density. This pro-vides a new approach with potential for microelectronic andoptical devices on the basis of electropolymerization. As forchemical synthesis， the fabrication of self-assembled conduct- ( [ * ] P rof. L . Jiang， Prof . M. Wan， Dr. H. Qiu， Dr. J. Zhai， D r. S. L i Center of Molecular Sciences， Institute of Chemistry The Chinese Academy of Sciences B eijing 100080 (PR China) ) ( E -mail： j ianglei@iccas.ac.cn， wanmx@iccas.ac.cn ) ( [** T h ] e work was su p ported by th e National Natural S c ience F o undation of China (No. 2 9634020-2； N o. 2 9974037)， S tate K ey P r oject F undamental R esearch (G1999064504)， Special Research Foundation of National N a ture S ciences Foundation of C h ina and Ce n ter for Molecular Sciences， Ins t ituteof Chemistry， Chinese Academy of Sciences (No.CMS-CX2001). ) ing polymer micro/-nanotubes has been developed in ourin17，group.17.8 It provides an attractive， template-free， alternativeroute to nanotubes or -fibers， but obtaining oriented arrays isquite difficult. In this report， we demonstrate a simple and nov-el self-assembly process combined with a porous template toprepare highly oriented arrays of PANI nanowires. 2. Results and Discussion As the polymer to form nanowire arrays， aniline-4-(3-(4-((4-nitrophenyl)azo)phenyloxy)propyl)aminobenzene sulfonic acid(aniline/C3-ABSA) was chosen， which could be formed as freemicelles in aqueous solution and self-assembled to form PANI/C3-ABSA nanowires bythe addition of the oxidant(NH4)4S2O8 (APS)， as reported by us previously.17.8 A noveldopant was used in this fabrication and the chemical structureof a PANI nanotube is shown in Scheme 1. The diameter of thewires ranged from micrometers to nanometers (4 um to50 nm) depending on the synthesis conditions.[8，9，15] The details PANI： HN +NH AA-=C3-ABSA：02N- -N=N -OCH2CH2CH2NH SO3 Scheme 1.The chemical structures of PANI and the dopant C3-ABSA. of the experiment are given in the Experimental section. Inorder to obtain an ordered array structure， a hydrophilictrack-etched Al2O3 substrate with average pore diameter of200±30 nm and ca. 60 um thickness was immersed as a tem-plate into the emulsion of aniline/C3-ABSA. The self-as-sembled nanowires of PANI-(C3-ABSA) grow oriented per-pendicular to the AlzO template while the lengths of thesewires can be roughly controlled by controlling the polymeriza- tion time. When another dopant， naphthalene sulfuric acid(NSA)， was adopted，no aligned nanowires were obtained， in-dicating that different dopants may affect the self-assembledalignment of PANI. The structure of PANI-(C3-ABSA) nanowires was character-ized by Fourier transform infrared (FTIR) and UV-vis spec-trometry. FTIR spectra showed that the main chain is identicalto that of PANI synthesized by a common method， 16 while theposition of the benzene ring at 1578-1590 cmand the dopingbands at 1123-1142 cm- were slightly affected by the oxidationstate. The UV-vis absorption of PANI-(C3-ABSA) exhibitedthe doping state of the emeraldine salt form of PANI. Figure 1 shows scanning electron microscopy (SEM) imagesof an as-grown array of polyaniline tubes without the templatebeing removed. It can be seen that nanowires grow out of the Figure 1. SEM images of PANI-(C3-ABSA) nanowires/-fibers obtained by thecombined methods of self-assembly and template synthesis. A) PANI-(C3-ABSA) nanowires/-fibers grow out of the template and aggregate to formbunches on the micrometer scale (with surface cracks) without removal of thehydrophilic porous Al2O3 substrate. The polymerization time was 72 h. B) Anenlargement of (A). The diameter of the nanowires/-fibers ranges from 110 nmto 190 nm and the length is on the micrometer scale. template and aggregate to form bunches on the micrometerscale with surface cracks (Fig. 1A). These cracks were causedby shrinkage of the polymer during drying. The top of thesebunches was uniformly flat， indicating the even growth rate ofnanowires at the initial growth step. Figure 1B is a high resolu-tion image. The morphology of the nanowires can be clearlyobserved， and these nanowires protrude vertically from the sur-face of the porous Al2O3 template to form a 1D highly orderedarray. The diameter of the nanowires ranged from 110 to190 nm and the length (taken as that protruding out of theAl2O3 template) is on the scale of several micrometers， de-pending on the reaction time. With increasing polymerization time， the morphology of thenanowires changed from the 1D ordering of vertical alignmentto flower-like aggregated bunches (Fig. 2A). This phenomenoncan be attributed to the different growth rates of the wires；differences in diameter may lead to differences in length. At B Figure 2. A) SEM image of PANI-(C3-ABSA) nanowires after polymerizationfor 96.0 h. The nanowires/-fibers aggregate to form flower-like bunches. Thehydrophilic porous Al2Os template was not removed. B) The relationshipsbetween the polymerization time and the length (right) and diameter (left) of thenanowires/-fibers. the initial stage of growth，the length difference induced bythe different growth rates was not obvious， therefore a flat topsurface appeared. In this case， the nanowires grew in symmetri-cal interactions because of the close-packed hexagonal porestructure. After a long polymerization time， an obvious lengthdifference was produced， and asymmetrical interactions amongthese wires occurred. As a result，PANI-(C3-ABSA) nanowiresmay bend and aggregate to form disordered flower-like struc-tures as shown in Figure 2A， which results from a tendency ofthe wires to form a structure similar to that of wires grownfrom solution.[8 Thus the polymerization time influences thelength and arrangement of nanowires. In order to prove thisconsideration， the morphologies resulting from differentgrowth times of 24 h， 48 h， 72 h， 96 h， 120 h， and 144 h werestudied. The relationship between the polymerization time andthe length or diameter of the wires is shown in Figure 2B. It was found that these wires were situated in the pores of thetemplate when the growth time was less than 50 h. There wasno distinct growth out of the template. The length of the nano-wires varied from ca. 1 um to 10 um as the growth timechanged from 72.0 h to 144.0 h， while the diameters did notchange significantly. An ordered array of nanowires/-fibers canbe obtained when the polymerization time is 72 h. When the polymerization time was not long enough to letthe nanowires/-fibers grow outside the surface of Al2O3 (inFig. 3A)， it was found that most of the nanostructures withinthe pores were hollow tubes and the others were solid fibers Figure 3. A) SEM image of PANI-(C3-ABSA) nanowires when the polymeriza-tion time is 48.0 h. Most of the nanostructures are hollow tubes， labeled c， othersare solid fibers， labeled a. One tube/fiber grows in a pore with a regular hexagonshape， labeled c. Two or three wires grow in a pore with an irregular contour，l1abeled a and b. The shapes of some wires are similar to the shape of the pores，labeled c， indicating the growth is along the wall of the pores. B) A model of theformation mechanism of PANI-(C3-ABSA) nanowires. The micelles can be as-sumed to have a "head-tail" structure in which -SOH is assigned as a“tail"packed outside the micelles in a water system， while aniline is a"head" packedinside the micelles. The porous Al2Os template is hydrophilic. After the additionof oxidant and dopant (NH4)4S2Os， aniline-(C3-ABSA) self-assembled to formPANI-(C3-ABSA) nanowires/-fibers in the pores of the template，and grew ori-ented out of the template to form ordered arrays. (e.g.， Fig. 3A-a)， which is similar to self-assembly results pre-viously reported by us. Evidently， the diameter of these wiresis smaller than that of the pore， which could be attributedeither to the shrinkage of the nanowires as the sample dried orto the enlarged pore size of Al2O3 in acidic polymerizationsolution to some degree. However， the shapes of some wireswere similar to the shapes of the pores (e.g.， Fig. 3A-c). Thisalso suggested that an interfacial effect played an importantrole during this assembly process. A thin surface film may cov- er the pore walls in the initial stages of wetting， because thecohesive driving forces for complete filling are much weakerthan the adhesive forces.i In some cases， one wire grew in asingle pore. But there were also examples of two or three wiresgrowing in one pore. Detailed observation revealed that if apore was a regular hexagon in shape， only one nanotube/-fibergrew in it； if a pore had an irregular contour， then two or morenanowires were produced in the pore (e.g.， Fig. 3A-b). Thiswas different from the results 7] obtained simply by using po-rous Al2O3 as a conventional template， in which only one tubeor fiber can be formed in a pore of a template， indicating thecombination of the effects of both self-assembly and the porecontour of the template. A model to illustrate the formation ofthe 1D oriented and highly ordered array of nanowires is pro-posed in Figure 3B. In general， the polymerization takes placeafter the precursors enter the pores of the template. In thiscase， the free micelles8of aniline/C3-ABSA with hydrophilic(-SO；H) tail and hydrophobic head were formed in emulsionat the initial step. These amphiphilic micelles can be easilyintroduced into the hydrophilic pores through the driving forceof interfacial attraction， one， two， or three being incorporated，depending on the curvature and interfacial hydrophilic prop-erty of the pores. It should be noted that no oriented arraycould be grown when the template was treated to be hydropho-bic. The self-assembled nanowires were randomly distributed，lying on the surface of Al2O3 template (shown in Fig. 4) similarto the morphology of wires formed in solution. Evidently， it isthe interfacial hydrophilic behavior that controls the orienta-tion during the self-assembly process， and hence ordering ofthe nanowires. The template played an important role at thisstage. Then the nanowires grew oriented along the direction ofthe pore wall as the result of the interaction between wires andtemplate， and self-assembly was the main process of the growthat this step. Figure 4. SEM image of PANI-(C3-ABSA) synthesized in the presence of hydro-phobic porous Al2O3 substrate. The self-assembled nanowires were randomlys Wdistributed lying on the surface of Al2O3 template similar to the morphology ofwires formed in solution. 3.Conclusion In summary， oriented nanowires of polyaniline with highlyordered structures were obtained by using a self-assembly syn-thesis method on a hydrophilic porous Al2O3 template. The combination of self-assembly growth with a template allowsthe simple creation of large-scale oriented nanowires withoutremoval of the template. It is essential that a self-assembly sys-tem adequately matches the porous template (hydrophilicityand hydrophobicity) in terms of interfacial effect. This methodcan also be used for many other polymers， which can formtubes or fibers by self-assembly，[15，18，19] on the basis of the inter-facial effect between self-assembly system and porous templateto form 1D-ordered nanostructures， which may have potentialapplications in field-effect and photoelectric devices， etc. 4. Experimental 4-(3-(4-((4-Nitrophenyl)azo)phenyloxy)propyl)aminobenzene sulfonic acid(C3-ABSA) was designed and synthesized by the reaction of 3-bromide-1-(4-((4-nitrophenyl)azo)phenyloxy)propane (B3) with sodium p-aminobenzene sulfonicacid (ABSA) and acidification with hydrochloric acid. The molecular weight andformula of C3-ABSA were measured by negative secondary ion mass spectrome-try to be ca. 455 and C21H20N4O，S， respectively. In a typical experiment， aniline (0.2 mL)， C3-ABSA (5.0 mg)， and deionizedwater (1.0 mL) were mixed to form a homogeneous emulsion under ultrasonicstirring for about 0.5 h. The porous，hydrophilic Al2O3 template was immersed inthe above emulsion with ultrasonic stirring at room temperature for about 1.0 hin order to fill the emulsion into Al2O3 pores. Then， aqueous APS (1.2 mL，0.5 M) pre-dissolved in deionized water was added rapidly. 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WILEY-VCH Verlag GmbH & Co. KGaA， WeinheimAdv. Funct.Mater. No. December WILEY-VCH Verlag GmbH & Co. KGaA， Weinheimhttp：//www.afm-journal.deAdv. Funct. Mater.No.December