Materials Science and Engineering B 134 (2006) 919

Review

Synthesis and applications of one-dimensional

Abstract

This papepotential apsynthesis acapproachesarrays on a lone-dimensienvironmendigital nonv 2006 Else

Keywords: Polyaniline; Synthesis; Template; Nanofiber; Nanotube; Nanowire; Surface area; Sensor

Contents

1. Introd2. Synth

2.1.2.2.2.3.2.4.2.5.

3. Prope4. Appli

4.1.4.2.4.3.4.4.4.5.

CorresponE-mail ad

0921-5107/$doi:10.1016/juction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10esis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Hard template synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Soft template synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Combined soft and hard template synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Seeding polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13No-template synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.5.1. Interfacial polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.5.2. Radiolytic synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.5.3. Rapid mixing reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.5.4. Sonochemical synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.5.5. Electrochemical approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

rties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Sensor application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Energy storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Field emission application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Flash welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Digital nonvolatile memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

ding author.dress: victordhzhang@126.com (D. Zhang).

see front matter 2006 Elsevier B.V. All rights reserved..mseb.2006.07.037nano-structured polyaniline: An overviewDonghua Zhang a,, Yangyong Wang b

a School of Materials and Chemical Engineering, Xian Technological University, Xian 710032, PR Chinab School of Energy and Power Engineering, Xian Jiaotong University, Xian 710049, PR China

Received 9 February 2006; received in revised form 28 July 2006; accepted 28 July 2006

r summarizes and reviews the various synthesizing approaches of one-dimensional nano-structured polyaniline (PANI) and severalplications of the nanomaterial. The synthesizing approaches can be generally categorized into template synthesis and non-templatecording to whether template(s), hard (physical template) or soft (chemical template), is (are) used or not. However, though the variousestablished, preparation of one-dimensional nano-structured PANI with controllable morphologies and sizes, especially well orientedarge scale is still a major challenge. Furthermore, the formation mechanisms of the nanostructures are still unclear. On the other hand,onal nano-structured PANI exhibits high surface area, high conductivity, as well as controllable chemical/physical properties and goodtal stability, rendering the nanomaterial promising candidate for application ranging from sensors, energy storage and flash welding toolatile memory.vier B.V. All rights reserved.

10 D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919

5. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction

Intrinsically conducting polymers, including polyacetylene,polyaniline (PANI) (Fig. 1), polypyrrole, polythiophene, poly(p-phenylene-vinylene), etc., are termed organic polymers thatpossess the electrical, electronic, magnetic, and optical proper-ties of a meability, etc.and more cpolymers,conductivitto its wideregime, unlow cost, eious fields,magnetic isensors [7]derivativeschemical osome otherelectrolesstion [14,15infusibilityapplicationpolymers waddress thipoint of viePANI, on oblend of Pimprove thspecial phymaterial wider it for neconversionelectronicsPANI nanotechnique aof a recentincluding nrils, nanobfabricating

Fig. 1. M(b) form,

connectionobjective osynthesis aPANI. It shto provideinevitable d

hes

frha4],eno te w

ona

uctes,n th

ernthpringizame

heste

rd

aretings inof

oditerins wpin

. Hted

theaytal while retaining the mechanical property, process-commonly associated with a conventional polymer,ommonly known as synthetic metals [1]. Of thesePANI has elicited the most interest since its electricy was found by MacDiarmid et al. [2] in 1985, duerange of conductivity from insulating to metallic

ique redox tunability, good environmental stability,ase of synthesis, and promising applications in var-such as metallic corrosion protection [3,4], electro-

nterference shielding [5], electrostatic discharge [6],, actuators [8], to mention just a few. PANI and itsare generally synthesized by chemical or electro-

xidative polymerization of the monomers, althoughapproaches such as plasma polymerization [911],polymerization [12,13] and solid-state polymeriza-] were also reported. Note that the intractability, i.e.,and insolubility, is the main factor that hampers thes of PANI, dispersing of the polymer in conventionalas considered one of the most effective approaches to

s problem from both the scientific and technologicalw [3,16]. Accordingly, synthesis of nano-structuredne hand, is the key step in preparing highly dispersedANI with other processable polymers, and thus toe processability of PANI. On the other hand, somesical and chemical properties differing from the bulkll be achieved on nano-structured PANI and will ren-w applications [17], such as chemical sensors, energyand storage, light-emitting display devices, micro-

, optical storage, and so on. In comparison with theparticles, which are mainly synthesized by dispersionnd electrochemical method and have been the subjectreview [18], one dimensional nano-structured PANI,anofibers, nanowires, nanorods, nanotubes, nanofib-

elts and nanoribbons, presents several advantages innano-devices and in preparing nanoscale electrical

subject.

2. Synt

Asideand mecroute [2one-dimrized intoxidativconventithesizingnano-strcategorithesis, iThe form[25]) sythesis apthe reactpolymerreactionapproacand hard

2.1. Ha

The hMartinconductmaterialchannels[42], anof the intivenessmaterialFor examachievedcate [42]a ratherremove

mers mstructures aTypicall

cooled acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

s in highly conducting polymer composites, etc. Thef this paper is to review the past works concerning thend applications of one-dimensional nano-structuredould be emphasized that the paper is only intendeda brief summary of the literature and omissions areue to the myriad of investigations carried out on this

is

om the physical routes like electrospinning [1922]nical stretching [23], and the doping induced solutionthe chemical approaches adopted for production of

sional nano-structured PANI can be generally catego-he chemical oxidative way and the electrochemicalay, just as that occurred for the synthesis of the

al PANI powders. While in this review, the syn-pproaches used for production of one-dimensionalured PANI, as detailed below, are divided into twoi.e. the template synthesis and the no-template syn-e light of whether template(s) is (are) used or not.is subdivided into hard template (physical template

esis and soft template (chemical template [25]) syn-oach according to the solubility of the templates inmedia, while the latter is subdivided into interfacial

tion [17,26], radiolytic synthesis [27], rapid mixingthod [28] and sonochemical synthesis [29,30]. Otherlike seeding polymerization [31] and combined soft

mplate synthesis [32] were also reported.

template synthesis

d template synthesis method, which is proposed byal. [3337], involves synthesizing the intrinsicallypolymers like PANI, polypyrrole, as well as othercluding metals [38,39], carbons [40,41], in the pores,hard templates such as membranes [3537], zeolitesc aluminum oxide (AAO) [4345], and so on. Oneesting and useful features of the method is its effec-preparing one-dimensional micro- or nano-structuredith controllable diameter, length and orientation [43].

le, PANI filaments with diameters of 3 nm have beenthe hexagonal channels of mesoporous aluminosili-owever, the disadvantage of the method is that, firstly,ious post-synthesis process is required in order totemplates [46]; secondly, the nano-structured poly-be destroyed [47] or form undesirable aggregated

fter released from the templates [48].y, the hard templates were firstly immersed in a pre-ic solution of aniline, and the oxidant solution at theolecular structure of PANI in emeraldine base (a) and emeraldine salt

where A represents the dopant anion. same temperature was added then to start the polymerization.

D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919 11

During the procedure, PANI was produced and deposited withinthe pores or channels of the templates. With the templates elim-inated, parPANI wasremoved, gPANI filledwas adsorbplates, andfashion assynthesizedoxydisulfatthe particlewhich servoxidant difreacted, yiebrane. In apolymerizawere also pwith hard tnanochann

With anotubules enet al. [52]were protecnanotubuleing materiand magneparticles, wnanofibers

2.2. Soft te

The softemplate-frthe literatusizing the Pof structurdeoxyribonthiolated ccrystallineproductiontants are ofnaphthalenacid (CSAchiral 2-pynitropheny(C3-ABSAacid (AM(ANSA) [5acid), polysimple andbecause itthe wearisoone-dimention conditratio of anlower conc

otubes [77] or nanofibers [68], while the higher concentrationsdid the granular PANI.

typuch ath did warmedeousempethee, t

-dimpreps we

thodner d

pectl. [6NAcon63]. Viameith

meteobe

berst al. [er,

anothd inuch, an

r abesule (Hare

/nanbersnt ddopimorpcern

propledredty os [7meners aer wmole an

ratio, whas p

he sthetly or completely, one-dimensional nano-structuredisolated [44]. Occasionally, the templates were notiving rise to the one-dimensional nano-structuredcomposite materials [42]. In some cases, aniline

ed from vapor phase into the channels of the tem-polymerization was then carried out in an identical

mentioned above [42]. PANI nanotubules were alsoby placing solutions of aniline and ammonium per-

e (APS), the oxidant, in a two-compartment cell withtrack-etched membrane (PTM) as the dividing wall,

es as the hard template [49]. The monomer and thefused toward each other through the membrane andlding the PANI nanotubules in the pores of the mem-ddition to the above-mentioned chemical oxidativetion, PANI nanofibers, nanotubules and nanoribbonsrepared by electrochemical oxidative polymerizationemplates such as PTM [49], AAO [50] and enclosedels [51].alumina membrane as the hard-template, PANI nan-capsulated nickel nanowires were prepared by Caothrough a two-step process. The nickel nanowirested from corrosion and oxidation in air by the PANIs, rendering the nano-structured composite promis-al for some applications such as microelectronicstic antenna material. Inorganic particles, such as Niere also used as templates in synthesizing PANI

[53].

mplate synthesis

t template synthesis method, always called theee method [5457] or self-assembly method [58] inres in that no hard templates is used, entails synthe-ANI, as well as polypyrrole [55,59], in the presencee-directing molecules such as surfactants [60,61],ucleic acid (DNA) [62,63], polyelectrolytes [64],

yclodextrins [65], sulfonated porphyrin [66], liquid[67], and ethanol [68,69], which act as templates forof the one-dimensional nanomaterials. The surfac-

ten complex acids with bulky side groups, such as theesulfonic acid (NSA) [56,70,71], camphorsulfonic) [7275], azobenzenesulfonic acid (ABSA) [76],rrolidone-5-carboxylic acid (PCA) [77], 4-(3-(4-((4-l)azo)phenyloxy)propyl)aminobenzene sulfonic acid) [32], 2-acrylamido-2-methyl-1-propanesulfonicPSA) [78], 5-aminonaphthalene-2-sulfonic acid7], etc. The polyelectrolytes include poly(acrylic

(styrenesulphonic acid), etc. [64,79]. The method ischeap in comparison with the hard template methodomits the use of the hard templates and thereforeme post synthesis processing. The formation of the

sional nano-structured PANI depended on the reac-ions, such as the concentration of aniline, the molariline to oxidant or the soft template. Generally, theentrations of aniline favored the formation of nan-

In atants setc. widistillewas foan aqusame tinitiatetion timthe onegroup[56], athis mewith inand asels et awith Don siliplate [with deters wthe diap-aminnanofiYang emonom

Inmerize[58] sH3PO4ence o

benzenbromidto prepotubesnanofiDiffereby a deof the

Conit wasassembstructuproperfactantone-didiametpolymplates,and timmolarformedPANI w[72]. T[57] asical surfactants based procedure, aniline and surfac-s CSA, NSA, ANSA, o-aminobenzenesulfonic acid,

fferent molar ratios were added to a certain amount ofter. A transparent solution of aniline/surfactant saltand was brought to a specified temperature. Then

solution of oxidant, usually APS, pre-cooled to therature was added to the above transparent solution to

polymerization. After a predetermined period of reac-he mixture was filtered, washed, and dried to obtainensional nano-structured PANI. For instance, Wansared both nano- and micro-structured PANI tubesll as polypyrrole tubes [55], with various acids by. Yang et al. [77] synthesized chiral PANI nanotubesiameter of 50130 nm, outer diameter of 80220 nm

ratio of 610, with chiral PCA as the template. Nick-2] and Ma et al. [63] synthesized nanowires of PANIas the template, and the nanowires were immobilizedsurface with pre-stretched strand DNA as the tem-ery recently, Li et al. [80] prepared PANI nanofibers

ters of 100120 nm and lengths of several microm-p-aminobenzenesulfonic acid as the surfactant, andrs of the nanofibers decreased with decreasing of the

nzenesulfonic acid concentrations. Self-doped PANIwith a diameter of 120370 nm were synthesized by81] with o-aminobenzenesulfonic acid, a self-doping

as the surfactant.er surfactants based procedure, aniline was poly-acidic solution, including both the inorganic acidsas hydrochloride acid (HCl), H2SO4, HBF4 andd organic acids such as AMPSA [82], in the pres-sence of the surfactants, such as sodium dodecyl-fonate (SDBS) and hexadecyltrimethylammoniumTAB) [58], Triton X-100 [82] or Allura Red AC [83]one-dimensional nano-structured PANI. Both nan-orods with average diameter of 150340 nm [58] andwith average diameter of 56 nm [82] were obtained.opant anions can be introduced to the nanomaterialsngredoping procedure without significant changinghologies and diameters of the nanostructures.ing the formation mechanisms of the nanostructures,

osed, but not confirmed [84], that the surfactants self-with or without their aniline salts into nano- or micro-intermediates [70,76,84,85] due to the hydrophobicf aniline and the hydrophilic property of the sur-0], which played a template role in forming of thesional nano-structured PANI [48,54,58,86,87]. Thend lengths of the one-dimensional nano-structuredere depended on the factors such as the soft tem-ar ratio of surfactant to aniline, reacting temperatured other synthetic conditions. For example, when theof CSA to aniline was fixed at 2, granular PANI wasile in decreasing of the ratio from 1 to 0.01, tubularroduced with diameters decreased from 180 to 85 nmame result was obtained with NSA [48] and ANSAsoft templates. With decreasing of the molar ratio of

12 D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919

NSA to aniline from 2 to 1 and 0.5, tubular PANI with averagediameters of 650, 154 and 92 nm, respectively, was obtained.While withwith averaof ANSA [molar ratioWhile decrcylinders awere obserlar PANI.systems bediameters oIn spite of tmation of Pout recentlity conditionature of tproduced wof sulfuricof 100300of several m

While itrolyte watetrahydrofthen addedcomplex oftetrahydrofplex was rethe additioated. Reactcollected bwas suggestrolytes, fopolyelectrowith diammolecule isglobular mformation o

One-dimduring elelated cyclotalline [67the gold elcyclodextriPANI withnano-ringsof 3.4m.ited much slengths thacrystallinewith diameobtained. Tcounter elequality nanbetter alignordered andthe templat

100 nm were obtained and it was revealed that both the electricquantity in electropolymerization and the ethanol affected the

ologSEMservmin

00 nmason

anoH-boPAN

the isencnano

reser, ns of 2ive pariouNI n. Thenano

tingtemitio

so bredy on

, a kid pyt wa

was

ligneorp

re imtersetersl surfniumC [ecrenano

0.05ltrim

hick00 nmed bB v

articlCT

re, itle in

omb

rdermethfurther decreasing of the ratio to 0.25, nanofibersge diameters of 76 nm were produced. In the case57], irregular granular PANI was obtained when theof ANSA to aniline falls in the range of 0.250.5.

easing of the ratio to 0.1 and 0.02, very short PANInd PANI nanotubes with outer diameter of 60100 nmved, respectively, and both coexisted with granu-Besides, adding of water to the aniline/surfactantsfore initiation of polymerization decreased also thef PANI tubes from micrometers to nanometers [54].he above-mentioned proposals and results on the for-ANI nanostructures, Konyushenko et al. [88] pointedy that morphology of PANI depends on the acid-ns during the reaction rather than on the chemical

he acid adopted. For example, granular PANI washen the polymerization was carried out in solutionsacid, while PANI nanotubes with external diameternm and internal diameter of 20100 nm, and lengthicrometres were obtained in solutions of acetic acid.

n a polyelectrolyte based procedure, the polyelec-s firstly dissolved in an organic solvent, such asuran, to give a homogeneous solution. Aniline wasto the solution to form a gel composed of a molecularaniline and the polyelectrolyte. After washed with

uran to eliminate the excess of aniline, the gel com--dissolved in an acidic aqueous solution. Followingn of the oxidant solution, polymerization was initi-ed for a specific period of time, PANI nanofibers werey filtration. As far as the mechanism is concerned, itted that aniline was firstly bound onto the polyelec-llowed by polymerization of aniline attached to thelyte templates [64,79]. Therefore, PANI nanofibers

eters of 50 nm were produced when the templatean extended linear chain of poly(acrylic acid), while

orphology was obtained when the random coil con-f poly(styrenesulphonic acid) was used as template.ensional nano-structured PANI was also reported

ctrochemical polymerization of aniline with thio-dextrins [65], sulfonated porphyrin [66], liquid crys-], or ethanol [68], as the soft templates. Modifiedectrodes with self-assembled monolayer of thiolatedns, Choi and Park [65] prepared both nanowires ofdiameter of ca. 70 nm and length of 1.5m, andof PANI with diameter of ca. 85 nm and lengthThe potentiodynamically grown nanowires exhib-moother morphology with fewer defects and longern those galvanostatically grown ones. When liquidwas adopted as the template [67], PANI nanowirester of 5070 nm and lengths of several microns werehe distance between the working electrode and thectrode played an important role in depositing highowires. Generally, reduction of the distance favoredment of the liquid crystalline, and therefore well-longer nano-wires of PANI. In the case of ethanol as

e [68], PANI nanofibers with diameters smaller than

morphtion inwas obwith 30than 1The rethe ethstrongtion ofhand,the prePANIstructuin watlengthoxidatwith vthe PAcyclesof theindicaas soft

Addcan alstructupholog(SDS)orienteoxidanstratewell aother m

Modiamenanom

specialammoat 7with dPANItion ofby cetywith t3004preparof CTAnanop0.25 Mperatulike ro

2.3. C

In onovely of the final PANI. For example, 90% (area frac-images) of nanofibers with diameters of 2050 nm

ed on platinum deposited quartz substrate electrodeof polymerization, while fibers with diameters largerwere obtained with polymerization time of 15 min.

for the formation of nanofibers was, on one hand,l molecules wrapped the PANI particles due to thending between them and prevented thus the aggrega-I particles during their polymerization, on the other

ncreased forming rate of crystalline nucleus due toe of ethanol is favorable for electrosynthesizing offibers. Thanks to the one-dimensional aggregationof 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinanorods of PANI with diameters of 2050 nm and001000 nm were also prepared by electrochemical

olymerization in the presence of sulfonated porphyrins porphyrin concentrations [66]. The aspect ratios ofanorods were affected by the sweeping potentials anddensity of the PANI nanorods, i.e. the crowdednessrods, increased with the concentrations of porphyrin,that the aggregated sulfonated porphyrin functionedplate in directing the morphology of PANI.nally, the equilibrium adsorbed surfactant aggregatese used as soft templates for synthesizing nano-PANI, as well as polypyrrole, with controlled mor-flat surfaces [60]. Aniline and sodium dodecyl sulfatend of surfactant, were allowed to aggregate on highlyrolytic graphite surfaces in the first step, and then thes added to start the polymerization. Finally, the sub-rinsed to remove the excessive ingredients, resultingd PANI nanowires parallel to the surface, as well ashologies on the substrates.portantly, uniform dendritic PANI nanofibers, with

and lengths of 6090 nm and several hundreds of, respectively, were chemically synthesized with aactant gel formed by a mixture of hexadecyltrimethy-

chloride (C16TMA), acetic acid, aniline, and water89]. The lengths of the PANI branches decreasedasing of the C16TMA concentration, and finallyparticles were resulted with a C16TMA concentra-mol/L. However, when the C16TMA was replacedethylammonium bromide (CTAB), PANI nanobelts

ness, width, and length in the range of 4050,, and about several micrometers, respectively, were

y the same group at 7 C with the concentrationary from 0.05 to 0.25 M [90]. Note that only PANIes with diameters of 70100 nm were obtained with

AB when the synthesis was carried out at room tem-was assumed that the surfactant played a template-the synthesis of PANI nanobelts.

ined soft and hard template synthesis

to fabricate highly oriented PANI nanostructures, aod combing the soft and hard template synthesizing

D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919 13

technique was employed [32]. Typically, aniline and the surfac-tant, e.g. C3-ABSA, was dissolved in deionized water to form ahomogenoutemplate, eemulsion aAPS solutiWith differnanofibersNo orientesoft templasolely, reveof the hardnanotubes.in a regularshaped porpore duringcated that bof the nanonanotubes ction time.

2.4. Seedin

By addinnanofibersotubes bunin diameter15 nm, inet al. [31].for preparaof these sesolution ofa solution otiate the poPANI was iThe morphlar with fibwhen the reticulate PAmorphologOne of thetities of dowithout thefor tediousnanoparticlnanotubesnanofibers.PANI nanowith APS ature of aniliinduction pdirecting th

2.5. No-tem

To distinthesis of th

template synthesis was coined here to name the method for syn-thesizing one-dimensional nano-structured PANI without any

tes,

Inteiallycialed wwhit theanofirodud fatructtyprganater

, suc

arioueous, sulen, tsuchlay

ctionuntilark-ged arem

nano

ed Pyzinonsiterfagro

synthofibe, menano

he inhilicfromnterfar aerizaned,e simin the diffecle, thpercacidnm,

d CSctioniums emulsion and ultrasonicated for a while. The hard.g. a porous, hydrophilic Al2O3, was immersed in thend ultrasonicated for another while. Afterwards, theon was added rapidly to initiate the polymerization.ent reacting time, the oriented PANI nanotubes andwere produced within the pores of the hard template.d nanofibers was obtained neither with NSA as thete nor with a hydrophobic Al2O3 as the hard templatealing that both the dopant and the surface propertytemplate affect the alignment of PANI nanofibers orThe fact that one nanotube or nanofiber was grownhexagon shaped pore, and two or more in a irregular

e, differing from the fact that one fiber or tube in onethe direct use of Al2O3 as the hard template, indi-

oth the soft and hard template affected the formationfibers or nanotubes. The lengths of the nanofibers oran be roughly controlled by varying the polymeriza-

g polymerization

g a small amount of various nanofibers like the PANIin diameter of 50 nm, the single-walled carbon nan-dles in diameter of 20 nm, nanofibrous hexapeptideof 12 nm, and the V2O5 nanofibers in diameter ofto the reacting solution of aniline and APS, Zhanginvented the so-called nanofiber seeding methodtion of PANI nanofibers. Typically, about 14 mgeding nanofibers were added firstly into a stirredaniline (0.14 M) in hydrochloric acid (1.0 M), andf 0.04 M APS was added then to the mixture to ini-

lymerization. The resulting dark-green precipitate ofsolated after 1.5 h and dried under dynamic vacuum.ology of all the seeded PANI products was fibril-er diameters in the range of 2060 nm. In contrast,action is seeded with spheres, for example, the par-

NI and the nanospheres of polypyrrole, nanofibrousy was obtained just like that in the unseeded reaction.advantages of the seeded approach is that bulk quan-ped PANI nanofibers could be produced in one stepneed of conventional templates, and hence the needpost-processing. Besides, PANI oligomers [91], Aues with average diameters of 15 nm [92] and carbon[93] were also used as the seeds in preparing PANIVery recently, Zhang et al. [94] confirmed that the

fibers prepared in chemical oxidative polymerizations the oxidant were resulted from the rodlike struc-niumperoxydisulfate ion clusters formed during theeriod, which acted as the in situ generated seeds ine morphology of the final product.

plate synthesis

guish from the commonly called template-free syn-e soft template synthesis method, the phrase no-

templa

2.5.1.Init

interfadissolvphase,films aboth nwere peral annano-s

In ain the othan whigherwith van aquas HClAnd thvesselthe twothe reaphasewith dcollecttion toPANIDedopor dial

In cthat inondarytionalof nanphasesPANIfrom thydropdrawnat the i

Aspolymconcer

producfectedboth thwere a

exampCSA,nitric3050HCl anthe fraof medhard or soft.

rfacial polymerization, PANI or its composite films were produced viapolymerization approach in which aniline was co-ith the surfactant [95] or polymers [96] in the organic

le APS in aqueous acidic phase, giving rise to theinterface of the two immiscible liquids. However,

bers [17,25] and nano-particles [97] of the polymerced recently, rendering the approach one of the gen-cile among a variety to synthesize one-dimensionalured PANI.ical reaction [17,26,93,98,99], aniline was dissolvedic phase, which can either be one with density lowersuch as hexane, benzene, toluene, etc. or be one

h as carbon tetrachloride, methylene chloride, etc.,s concentrations. Meanwhile, APS was dissolved inacid solution, covering a great variety of acids such

furic acid, CSA, toluene sulfonic acid, among others.he two solutions were gently transferred to a reactionas a beaker or a vial, generating an interface between

ers. Green PANI was formed firstly at the interface asproceeds and migrated gradually into the aqueousthe whole aqueous phase is filled homogeneouslyreen PANI at last. Finally, the aqueous phase was

fter sufficient time of reaction by dialysis or filtra-ove the impurities like excess dopants, etc., yieldingfibers in the form of a water dispersion or powder.ANI nanofibers can be obtained by further washingg with ammonia.deration of the formation mechanisms, it was revealedcial polymerization suppressed effectively the sec-wth of PANI, which occurred naturally in the conven-esis of PANI, leading thus to the exclusive formationrs [28]. The monomer and oxidant, separated in twot only at the interface and reacted there then, formingfibers. The nanofibers formed moved away rapidlyterface and diffused into the water phase due to theirity. As such, the nanofibers were continuously with-the interface, allowing formation of new nanofibers

face.s the synthesizing parameters (such as the solvents,tion temperature, and monomer concentration) areit was demonstrated that all aqueous/organic systemsilar PANI nanofibers, whose morphology was unaf-e subsequent dedoping process [17,98]. However,

ameters and the quality/uniformity of the nanofibersted by the acids and their concentrations [98]. Fore average diameters of the fibers synthesized in HCl,

hloric acid, and other acids (such as sulfuric acid,and 4-toluenesulfonic acid) are 30, 50, 120, andrespectively [98]. In the case of strong acids likeA, the lower the concentration of the acid, the lowerof nanofibers in the final product. While in the caseor weak acids like tartaric acid or pyrrolidone-5-

14 D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919

carboxylic acid, the products were mixtures of nanofibers andparticles even at high concentrations. It was therefore stated thathigh concePANI nano

The diammerizationlike AMPS[25]. The soctylphenoPolyethylesingle-tailelike potasstailed), potwin-tailedOT (AOT)syringed inthe case, jufibers obta23 nm, sm1.0 M CSAoriginate frthan that oof the CSAfactants incsingle-taileon fiber diathe averagelength, theage diametno surfactasurfactantscase of thechain effecfrom 23 nmtwin-taile aAlthough tintrinsic pthis reversaside fromage dopingwith additipolymeriza

By placof 4-aminoization, Homesh of PAAu surfaceamine creaa great attePANI ontonano-patterexhibited btle changesdurability.dopant in ipared transtwo-dimen

unique and facile one in preparing robust conductive PANInanofibers-based composites.

Radthisl wan theM ay of

ters o% ofonce

n, ros ofal PAuctu

orlywel

at thdiatif th

thorsbledtion.gregnm

50atesan

bers.lso pAt tsizedateda sil

ters o

Raph thethanthates tobtaiPA

ineulestionng eNI nFored,

bers00 nming twhicempes fontrations of strong acids favored the formation offibers.

eters of the nanofibers prepared by interfacial poly-can be controlled by using surface active dopantsA or CSA, and surfactants in the aqueous phase

urfactants cover the single-tailed non-ionic ones likel ethoxylate Triton-X 100 and d-Alpha Tocopherylne Glycol 1000 Succinate (Vitamin E TPGS), thed anionic ones like DBSA, and the twin-tailed onesium cis-1,2-dipentylethene sulfonate (C5H11-twin-tassium cis-1,2-diheptylethene sulfonate (C7H13-) and sodium di(2-ethylhexyl) sulfosuccinate aerosol-. Solutions of the surfactants, if used, were gentlyto the aqueous phase layer, i.e. bottom phase inst below the interface. The average diameter of the

ined using 1.0 M AMPSA as the aqueous phase isaller than the 48 nm for the fibers obtained withas the aqueous phase. The reason was expected to

om the more efficient packing capability of AMPSAf CSA due to its more linear structure. In the case

based nanofibers, the single-tailed non-ionic sur-reased the average diameter to 80 nm, while thed anionic surfactants seemed to have no any impactmeter. However, the twin-tailed surfactants increaseddiameter to 30 nm, and the longer the alkyl chain

smaller the average diameters. For instance, the aver-ers of the CSA based nanofibers synthesized withnt, with C5H11-twin-tailed and C7H13-twin-tailed asare 48, 35 and 28 nm, respectively. While in theAMPSA based nanofibers, this trend of the alkyl

t was reversed. The average diameters increased(no surfactant) to 35 nm and 55 nm with C5H11-

nd C7H13-twin-tailed as the surfactants, respectively.hese surfactants might be expected to disrupt theacking properties of the AMPSA, the reason fored alkyl chain effect is not clear up to now. Andthe above-mentioned morphological effect, the aver-

percentage of the PANI nanofibers was loweredon of the twin-tailed surfactants during interfacialtion.ing an Au substrate with self-assembled monolayerthiolphenol at the interface of an interfacial polymer-pkins and coworkers [100] grafted a two-dimensionalNI nanofibers with diameters of 4050 nm onto thethrough the covalent bonding between PANI and theted by the 4-aminothiolphenol monolayer. It was ofmpt to pattern the one-dimensional nano-structuredsubstrates in an ordered form. In contrast to otherning techniques of PANI on Au surfaces, the methodoth improved physical (adhesion) and chemical (lit-of conductivity to a series of acid/base exposure)

With sulfonated polystyrene as both the host and thenterfacial polymerization, the same group [101] pre-parent conductive nanocomposites with well-definedsional PANI nanofibers, rendering the procedure a

2.5.2.In

in HC[27]. Iof 0.1phologdiame5vol.APS csolutiolengththe totlike strare poagreeding thby irranism othe auassem

irradiaical ag2040ters ofaggregthen innanofiwere a

[102].synthespin coface ofdiame

2.5.3.Wit

ratherAPS toand sizwere o

ducingof anilmolecmerizaresultithe PAvents.producnanofi1003accordPANI,other tmicelliolytic synthesismethod, the aqueous solution of aniline and APSs irradiated with gamma rays without any template

case of parent solutions with typical concentrationniline, 0.3 M HCl, and 0.0020.1 M APS, the mor-the final product was predominantly nanofibers withf 50100 nm and length of 13m, though less thanglobular structures were still presented. While withntrations in the range of 0.050.1 M in the parentdlike structures with diameters of 250500 nm and

510m were observed, which represent 5 vol.% ofNI. The selected-area electron-diffraction of the rod-res was comparable to that of the nanofibers, whichordered. Fourier transform infrared (FTIR) spectruml with that of the typically prepared PANI, indicat-e chemical structure of the fibers was not affectedon. No complete explanation for formation mecha-e nanofibers was provided up to then according to. However, the authors concluded that PANI self-when the polymerization was carried out with gammaIn addition, four to five times larger sized spher-

ates, as compared with the aggregate diameters ofwithout irradiation, and hollow spheres with diame-100 nm were observed with irradiation. The hollowtended to stick to and link spheres, which coalescedanisotropic fashion and resulted then, probably, thePANI nanofibers decorated with metal nanoparticlesrepared with the same gamma irradiation procedurehe same time, thin films of PANI nanofibers were

by the same group by ultraviolet irradiation of amixture of aniline nitric acid and APS on the sur-

icon wafer [103]. The nanofibers demonstrate typicalf 20150 nm and lengths of microns.

id mixing reactionsolution of APS mixed rapidly with that of aniline,the conventional slow addition of the solution ofof aniline, PANI nanofibers with comparable shapesthose of interfacial polymerization [17,98] method

ned, rendering this method the simplest one in pro-NI nanofibers [28]. Owing to the even distributionand APS molecules in the solution, all the initiatorwere consumed rapidly after the start of the poly-and the secondary growth of PANI was suppressed,xclusive nanofibers in the product. The growth ofanofibers was related with the polarity of the sol-

example, in aqueous systems, pure nano-fibers werewhile in ethanol and isopropanol, mixture of shortattached with irregular particles and agglomerates of

particulates were obtained, respectively. However,o Zhang et al. [58], the formation of nano-structuredh was synthesized in presence of H3PO4 without any

late, soft or hard, was expected to originate from thermed by anilinium cations, which acted as the tem-

D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919 15

plates in forming the nanostructures. In another similar study,chloroaurate acid was used as the oxidant [104]. PANI nanofiberswith diameters of 304was probabcles in direprocess of

Chiou adilute polytion contaiof APS inany disturbtuned by apCSA, methdiameters o72250 nmas explaineon the surfallowed PAcompetitioof additioncentration,

Very rection of PANduring thetioned propsmooth sursystem viamechanicaforced to coccurs on tof the primthe heterogwere produto hold fornanoparticlthe higher towing to thperature. Funiform tha

2.5.4. SonoBy drop

aniline solucedure, witwith higheet al. [29,30in the reacfollowing t(1) the conthe growththicker fibthicker fibecedure, irrcontinuallysonochemiof the prim

Sonocnd Ahe, Y.ht 200

andmativantathersn.

Elecde fches

ynthe10].eenyntht an

tives000 nbtainof uniform and oriented nanowires of PANI with diam-ess than 100 nm were synthesized by Liang et al. [116]u et al. [117] on a variety of substrates by a three-stepchemical deposition procedure, also without using anytes. Typically, a large current density was adopted for a(0.08 mA/cm2 for 0.5 h) to create the nucleation sites onstrates in the first step; in the second step, a reduced cur-nsity was followed (0.04 mA/cm2 for 3 h); finally, a muchd current was followed (0.02 mA/cm2 for 3 h). The step-rowth produced uniform and oriented nanowires on bothstrates and particles and textured surfaces. For example,

ires with diameters of 5070 nm and lengths of 800 nmrmed perpendicular to a Pt substrate. When the substrates

olloidal silica particles, the nanowires produced were ori-perpendicular to the particle surfaces. PANI nanowireslso fabricated to bridge a sharp scanning tunneling micro-tip and an Au electrode by electrochemical polymeriza-nd the diameter can be reduced by mechanical stretchingnanowires [23]. For example, assuming the volume of theters of 35 5 nm and gold nanoparticles in diame-0 nm were obtained. The formation of the nanofibersly owing to the catalytic effect of the gold nanoparti-ctional growth of the PANI, though the exact growththe nanofibers was not clear.nd Epstein [105,106] prepared PANI nanofibers bymerization, in which a small portion of acid solu-ning aniline was carefully transferred to the solutionacid and then leave the mixture to react withoutance. The diameters of the fibers can be roughlypropriate selection of the acids. For instance, whenanesulfonic acid and perchloric acid were used, thef the fibers were in the range of 1750, 4270 and, respectively. The formation of the nanofibers was,d, owing to the reduced numbers of nucleation sitesace of the nanofibers in a dilute condition, whichNI to grow directionally, differing from that of the

n between the directional growth and the formational nucleation centers in the case of high aniline con-which resulted irregular PANI product.ently, Li and Kaner [107] pointed out that the forma-I nanofibers was a result of homogeneous nucleation

synthesizing process, differing from the above men-osals. At the initial stages, PANI nanofibers with

faces and uniform sizes were formed in the reactiona homogeneous nucleation. When the system was

l stirred, the primarily formed PANI nanofibers wereollide into each other and heterogeneous nucleationhe surfaces of these particles, causing aggregationsary nanofibers; while when the system was left still,eneous nucleation was suppressed and nanofibersced continuously. The proposed mechanism appearsother materials such as poly(m-toluidine) and silicaes as per the authors. Besides, in absence of stirring,emperature favors more the homogeneous nucleatione faster formed embryonic nuclei than the lower tem-or instance, PANI nanofibers formed at 60 C is moren that formed at 0 C.

chemical synthesiswise addition of an acidic APS solution to an acidiction, just like the conventional PANI synthesis pro-h the aid of ultrasonic irradiation, PANI nanofibersr polymer yields were successfully prepared by Jing]. It was stated that three possible competitions existtion system if more aniline and APS are presenthe formation of the primary PANI nanofibers, i.e.tinuing formation of primary PANI nanofibers, (2)of the primary nanofibers into unevenly surfaced

ers, and (3) the growth and agglomeration of thers into irregular particles. In the conventional pro-

egular PANI particles were obtained owing to theoccurring of steps (2) and (3); while in the case of

cal synthesis, the further growth and agglomerationary nanofibers were effectively prevented, even more

Fig. 2.aniline aWu, L.SCopyrig

anilinethe forthe adwith oreactio

2.5.5.Asi

approaalso s[1081have bcally swithouderiva5002were o

arrayseters land Lielectrotemplawhilethe subrent dereducewise gflat subnanow

were fowere c

entedwere a

scopetion, aof thehemically prepared PANI nanofibers with secondary addition ofPS (Reproduced with permission from X.L. Jing, Y.Y. Wang, D.Guo, J. Polym. Sci., Part A: Polym. Chem. 44 (2006) 10141019.5 Wiley Periodicals, Inc. [29]).

APS were added into the system [29], resulting toon of more primary PANI nanofibers (Fig. 2). One ofges of the approach is its scalability in comparisonsuch as interfacial polymerization or rapid mixing

trochemical approachrom the above-mentioned chemical no-template, one-dimensional nano-structured PANI wassized by electrochemical no-template approachesPANI nanofibrils, as well as microfibrils or rods,

found by Langer et al. [111115] in electrochemi-esizing PANI from an aqueous medium at pH 1y templates. The nanofibrils doped with fullereneexhibited diameters of 10100 nm and lengths ofm [115]. Both single nanofibrils and their networksed with controlled charge flows [114]. Latterly, large

16 D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919

nanowires does not change during stretching, the upper limitdiameter of the PANI nanowires can be reduced from the initial20 to 6porous polfilms as theand then trPANI nanoapproach [

3. Propert

As reveX-ray diffr[27,31,68,8tubes [85]conventionstein shiftsoriginatedsome sma

chemical sPANI nanogested thatthe axis ofPANI nanoa highly orface, in whthe axis odisorderedstructures.thesized PAtivities decfinally reacder. This whighly ordeeters and flayer than[120]. Thefor electroc[51].

The fouof both grnanofibersthesized bydoping acisured electwas synthe[73,74], far[73,74,76]contact res

BrunauenanofibersFor exampwith diam37.2 m2/g,doped PANones, whicPANI.

4. Applications

rt frmengranuurfacred Pingstor

enso

elecicallor b24],e n

etc.,r se

akenor dtion

sionaon [2n decamI b

ampANInven

d Nin thsitivcknetionof thtion

r theurfaf neu0] anster rlm.

polyals anceorigne ad byed PAe are

powe

atertruc, ancallynm by stretching over a distance of 200 nm. Withy(styrene-block-2-vinylpyridine) diblock copolymer

templates, which were spin coated to the electrodeeated with acetic acid before hand, highly porousfiber films were also prepared by electrochemical

118].

ies

aled by the FTIR spectra, UVvis spectra, and theaction, all the PANI nanotubes [57,58], nanofibers2], nanowires [67], nanorods [58], as well as micro-

, have backbone structures similar to that of theal prepared granular PANI. In some cases, the Ein-

observed in the FTIR and UVvis spectra werefrom the interaction between the PANI chains andll molecules, such as ethanol [68], not from thetructures. For electrochemical prepared orientedwires [117], polarized infrared spectroscopy sug-the PANI molecules were aligned perpendicular tothe nanofibers. For the hard-template synthesized

- [36] and micro-tubes/fibers [119], they exhibiteddered layer (ca. 5 nm in thickness) on the outer sur-ich the PANI chains are aligned perpendicular to

f the nano- or micro-structures, and progressivelylayers toward the center of the nano- or micro-

Conductivity measurement of the hard-template syn-NI nanotubules [49,119] showed that the conduc-

reased with the increasing of the diameters, andhes the conductivity of the conventional PANI pow-as resulted from the decreasing proportion of thered layer in the materials with increasing of diam-rom the higher conductivity of the highly orderedthat of the disordered inner part of the fibers/tubesanalogous conductivity decrease was also observedhemically template-synthesized PANI nanoribbons

r-probe conductivity of the PANI pellet consistinganular particles and nanofibers [53], or the PANIpellet [31,61,91] was similar to their counterpart syn-the conventional procedure, and was affected by the

d and doping degree, and so on. The directly mea-rical conductivity of a single PANI nanotube, whichsized by the soft template method, is ca.30 S/cmmore higher than the 102 S/cm order of magnitudefor the nanotube pellet due to the large intertubularistance [73,74].rEmmettTeller (BET) surface area of the PANIdecreased with increasing of the fiber diameters [98].le, BET surface area of dedoped PANI nanofiberseters of 30, 50, and 120 nm are 54.6, 49.3, andrespectively. In addition, the BET surface area ofI nanofibers was lower than that of the dedoped

h is in consistent with the results of the conventional

Apaone-ditionallarge sstructupromisenergy

4.1. S

Theintrinsacidic[123,1as som

[129],rials foundertthe poconven

dimendiffusietratioand beof PANFor exized Pthe coHCl antwiceing senthe thiinteracinsideconven

thinnemost scase o

[26,11ited faPANI fiof themateriresistawhichbackboinducein dopsurfacthe new

Theport mmicrosferratechemiom the above-mentioned similar properties of thesional nano-structured PANI to that of the conven-lar PANI powders, several unique properties, such ase area, were exhibited by the one-dimensional nano-ANI, rendering this important class of new materials

candidates for applications ranging from sensors toages and electron field emissions.

r application

trical conductivity changing of PANI, as well as othery conducting polymers [121,122], upon exposure toasic vapors and liquids, such as HCl, ammonia gasor ammonia water [125,126], CO2 [127], as welleutral gases including chloroform [128], alcoholsrendered PANI one of the novel promising mate-

nsor applications, and tremendous works have beenon the field. However, poor sensitivity resulted from

iffusion of analyte molecules was observed for theal PANI and the composite films [130132]. One-l nano-structured PANI enhanced significantly the6,110,132] due to its greater exposure area and pen-

pth for gas molecules than the conventional PANI,e an alternative material to improve the sensitivityased sensors, especially for acidic and basic gases.le, the resistance response of the interfacial polymer-nanofibers based film was much faster than that oftional PANI based film on exposure to 100 ppm ofH3, although the nanofibers based film is more thanick [17]. In addition, the response and correspond-ity of the nanofibers based film was independent onss owing to its porous nature which facilitate theof vapor molecules with all the fibers, outside ande film. On the other hand, the performance of the

al PANI film was strongly thickness dependent. Thefilm, the better the performance in that only the out-ce interacts with the vapor molecules [132]. In thetral gas molecules, such as hydrazine [26], methanold water [110], PANI nanofibers based films exhib-esponses, but lower sensitivity than the conventionalThe reason lied in both the relatively open structuremeric materials as compared with metal or inorganicnd the adverse effect from the interfibrillar contactof the nanofibers based films [26,110]. If chirality,inate only from the helical conformation of polymernd/or from the helical packing of the polymer chainschiral acids due to the absence of asymmetric carbonNI, was imparted to the PANI nanofibers with high

as, chiral separation and biological sensors would betential areas for applications of the nanofibers [91].ll-aligned PANI nanowires were also tested as sup-ials for sensing applications due to their orientedture and high surface area [117]. Iron hexacyano-active ingredient for H2O2 detection, was electro-deposited in form of nanoparticles on oriented PANI

D. Zhang, Y. Wang / Materials Science and Engineering B 134 (2006) 919 17

nanowires to fabricate H2O2 sensors. The presence of the PANIimproved the stability of the iron hexacyanoferrate and loweredthe over-popractical sealmost linehexacyanoffor H2O2 s

4.2. Energ

PANI nasymmetricaavailable suplayed in agranular PAwas achievthan the 33powder. Thcould be bestorage dev

4.3. Field

Well-alitogether wielectron fielow threshdensity (5an attractivpreparationmechanication of field

4.4. Flash

Irradiatenanofibersto the highlconductivitnique for p[134]. Onenique is thaa photomasterns, diffewelding [1in creatingapplicationand actuato

4.5. Digita

PANI nananoparticlrication ofexhibited vbe switcheddifference

mechanism was attributed to an electric field-induced chargetransfer from the PANI nanofibers to the Au nanoparticles. The

ged rted t

nclu

-dimromdeviherschesd phd en

ds hatructallyge.

ructuhichI an.

wled

projaborTech

nce

.G. M

.G. M

.L.D.7318. Wes.Y. W.Y. W. Wizn.C. P. Lu,004). Mil

ons o.G. Pa.J. Cr997). Liao. CheGong

8719X. Hu005)Ana998)X. Hu003).K. B187..G. M.J. Piet. 11tential of H2O2, which are of great importance innsing and detecting of H2O2. The stable, reliable andar response of the composite sensor proved the ironerrate loaded PANI nanowires a useful configurationensors.

y storage

nofibers showed higher capacitance values and morel charge/discharge cycles due to their increasedrface area, in spite of their similar redox peaks dis-queous electrochemistry to that of the conventionalNI [31]. For example, a capacitance value of 122 F/g

ed for HCl doped PANI nanofibers, far more higherF/g in the conventional prepared HCl doped PANIese kinds of specific properties of PANI nanofibersneficial to development of the next-generation energyices [31,61].

emission application

gned PANI nanofibers, in shape of membraneth the hard template of AAO, were directly tested asld emitter [43]. The stable field emission behavior,old voltage (56 V/m) and high emission currentmA/cm2) of the membrane suggested the materiale field-emitting candidate. Furthermore, the easy, smooth and substantial surface, low cost, and good

l property of the material will be favored in fabrica-emission displays.

welding

d by a camera flash, a random network of PANIwas turned into a smooth and shiny film [133] duey efficient photothermal conversion and low thermaly of PANI, which demonstrated a versatile new tech-rocessing polymers into potentially useful structuresof the great advantages of the flash welding tech-t a certain area can be selectively welded by using ofk in fabricating polymer films into pre-designed pat-ring from other welding techniques like microwave35]. In addition, the technique offered a rapid routeasymmetric films, which are widely used in manys such as separation membranes, chemical sensorsrs [133].

l nonvolatile memory

nofibers (30 nm in diameters) decorated with Aues (1 nm in diameter) were also attempted for fab-plastic digital memory device [136]. The device

ery interesting bistable electrical behavior and canelectrically between two states with a conductivity

of about three orders of magnitude. The switching

prolonsugges

5. Co

Onemost ptronicand otapproaical anthe goomethonano-s

especichallennanostview, wof PANization

Ackno

TheKey LXian

Refere

[1] A[2] A

N1

[3] B[4] Y[5] Y[6] F[7] K[8] W

(2[9] M

ti[10] L[11] G

(1[12] C[13] Y[14] J.

1[15] J.

(2[16] J.

(1[17] J.

(2[18] D

8[19] A

NMetention time and good write-read-erase cycle resultshe device promising for digital nonvolatile memory.

ding remarks

ensional nano-structured PANI is one class of theising candidates for development of nano-sized elec-ces, sensors, supercapacitors, energy storage devicesdue to their high surface area, versatile synthesis, high conductivity, as well as the controllable chem-ysical properties by oxidation and protonation, andvironmental stability. Although kinds of synthesizingve been established, preparation of one-dimensionalured PANI with controllable morphologies and sizes,well oriented arrays on a large scale is still a majorFurthermore, the exact formation mechanisms of theres need to be elucidated from a scientific point ofwill be of great importance in morphological control

d other polymers prepared by precipitation polymer-

gment

ect was supported by Open Fund of Shaanxi Provinceatory of Thin Films Technology and Optical Test,nological University (No. ZSKJ200506).

s

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10771080.

Synthesis and applications of one-dimensional nano-structured polyaniline: An overviewIntroductionSynthesisHard template synthesisSoft template synthesisCombined soft and hard template synthesisSeeding polymerizationNo-template synthesisInterfacial polymerizationRadiolytic synthesisRapid mixing reactionSonochemical synthesisElectrochemical approach

PropertiesApplicationsSensor applicationEnergy storageField emission applicationFlash weldingDigital nonvolatile memory

Concluding remarksAcknowledgmentReferences