Microtubes of conducting polymers

ELSEVIER

Synthetic Metals 101 (1999) 708-711

Microtubes

of conducting

polymers

Meixiane Wan, Jie Huang,YouqingShen (OrganicSolid Laboratory, Institute of Chemistry,The ChineseAcademyof Sciences,Beijing, 100080,P. R. of China) l.

Abstract

A newsimplemethodtermedasin-situ dopingpolymerizationat presenceof specialorganicsulfonicacidsas dopantswasproposEd to synthesizeconductingmicrotubesof polypyrrole (PPy) and polyaniline (PANI). The resultingmicrotubesnot only show hi& conductivity at roomtemperature(e.g27 S/cmfor PPy and4 S/cmfor PANI), but alsoaresolublein someorganicsolvmts. Compared to “template synthesis+method, which is an effective methodto synthesizemicrotubesof conductingpolymers. the new method proposedby authorsis much simplerwithout usingtemplatemembraneand “molecularanchor”, which are requked for “fnnplatr synthesis”method. K~oVds: polypyrrole, polyaniline, Scanningtransmission electronmicroscopy

1. lutroduction

Organicmicrotubeshave attractedmuchattention because of their aspectsof applicationin drug delivery systems[l,2], microwavecomponentafter coatingwith metal,electronicand electro-opticaldevices[3].In general,only granularor fibrillar morphology was observed[4-6] for conducting polymers synthesizedby conventional chemical or electrochemical polymerization although the morphology dependson the polymerizationmethodsandconditions[7,8]. However,a seriesof papersconcerningorganicmicrotubes have been publishedin the literaturefg-121.Among them, “templatesynthesis”methodproposedby Martin et al.[12]. is an effective method to synthesize microtube of conducting pol?mersat the presenttime. In this method,the poresin a microporousmembraneare usedas templatesfor the tubule synthesis,and this method has been successfullyappliedto synthesizepolyacetylene[l3], poly(3-methylthiophene)[14], polypyrrole[l4,15] andpolyaniline[l5, L6] microtubes. The mainadvantageof the “template synthesis”methodis that the length and diameter of the resulting tubes can be controlled by the selectedmicroporousmembrane,thereby, more regular microtubes can be obtained. However. disadvantagesof this method are obvious as follows: (1) solublemicroporousmembraneastemplatemustbe used;(2) “molecularanchor”,whoserole isto bindthe nascentpolymer to the wall of microporousmembrane,is requiredwhen the diameterof microporousmembraneis in nanometersize due to capillary effect; (3) the template membranemust be removedafter preparationin orderto obtainpuretubes.In our 0379-6779/99/$ - see front matter 0 1999 Elsevier Science %A. All rights PII: SO379-6779(98)00302-6

laboratory, recently, authors found a nrw slmpk mctthod termed as “in-s&l dopingpolymerization” at the presenceof specialsulfonic acid as dopantscan be used to synthctrizc: conductingmicrotubesof polypyrrole(.PPp) and pol~~amlu~r (PANI). Comparedto “templatesynthesis” method.thr ntfw methodproposedby authorsis muchsimplerwithout ttlmplate membraneand “molecularanchor”. Moreover. the rrsultkg microtubes not only exhibite high conductivity at room temperature, for instance,27Skm for PPy anti -!,O Sk+ fol PANI microtube,but alsoare soluble in organicsolvrnt. for example,PPy is solublein In-crrsol. and PANI is solublein m-cresol,DMF, andDMSO, respectively. In this article, synthsis, structure characterizations.and electrical properties and solubilty of P.4NI and PPy microtubessynthesizedby the new methodare repot?eci.

2. Synthesis and Mor’pbology

It hasbeendemonstrated that the morphology of conducting polymers strongly dependson the synthetic method and conditions.aswell as dopantfeature. Thus, we first choose “in-situ dopingpolymeriztion” and“two-step method”to dope PPy, while PANI was doped by “id-.cit/c doping polymerization”, “immerse-doping method” and “grinddopingmethod”respectively. The schematicprocessesof these doping methodsare shownin Fignre 1. It wasfound that the tubular n~orpholo~~ could only be obtained by in-sitzc doping polymerization methodwhen the dopantis the same.On thr otherhand, 11si~1g

M. Wan

et al.

Metals

I Synthetic

101

(1999)

a) in-situ doping polymerization

@NH*

or

B

+ RS03H

s

708-711

method

$&

Or

ES(RSO3H)

b) two steps method

cl--

c) immerse method

NH:

APS, HCI o-25%

ES(HCI)

-

OH-

H ES(RSOd ES RSo’ o-25 Oc (ultrasonic agitation in acid solution)

H)

d) grind -doping method NH;

APS, HCI ES(HCI) o-25%

A-=

Cl;

OH__c

RSO> H ES(RSOa o-25 % (reaction in solid)

ES

H

RSO;

Figure 1. Schematic processes of different doping method used for PANI and PPy

other approaches, such as two-step doping for PPy, “ginddoping” and “immerse-doping” method for PAM, only granular morphology was obtained. Those results indicate that “itvsitu doping polymerization” is one of the prerequisites to obtain tubular morphology of PPy and PANI by the new method. Moreover, various sulfonic acids as dopants were selected to understand the influence of dopants’ feature on the morphology of the doped PPy and PANI. The molecular structure of the selected dopants are given in Table 1. It was very interesting to find that only NSA as dopant could obtain tubular morphology for both doped PANI and PPy by it?-situ doping polymerization, indicating NSA dopant is another prerequisite to obtain tubular molFhology by the new method. Thus. it is expected that cooperative “role” of NSA dopant with itt-.vtu doping polymerization tnight play a “templatelike” role to controll the formation of tubular morphology for the doped PANI and PPy by the new method.The detailed synthetic processes were reported previously[l7]. The typical tubular morphology (EM image) of the PPy-NSA and PANINSA by the new method are shown in Figure 2.

Table 1 Molecular

structure of the selected sulfonic acids as dopants

Sulfonic acids benzene sulfonic acid (MBSA) p-dodecyl benzene sulfonic acid (DBSA) p-naphathalene sulfonic acid WA) S-n-butyl naphthalene sufonic acid (BNSA)

p-methyl

S-sulfo-isophthalic w-v alizarin red acid (‘A.R.4)

acid

structure

710

M. Wan et (11. I Synthetic

a. PPy-NSA(larged

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IOI (1999)

b. PAWNSA(laged

by 2x 1OJ times)

Figure 2. TEM images of PANI-NSA

108-711

and PPy-NSA

by 5,. 10’ times)

microtubes by the new method

3. Structural Characterizations 4. Solubility and Electrical Properties Elemental analysis, FTlR, UV-Vis spectra. and X-ray d8raction were used to characterize the structure of the resulting microtubes of PANI-NSA and PPy-NSA by the new method. All of characteristic absorption of PANl in FTlR spectra, such as 1.562 cm-‘, 1481 cm-‘, 1299 cm-‘, 1243 cm-‘, 1129 cm’]. and S14 cm” were observed. which indicates the bone structure of PANI-NSA microtubes is similar to that of PANI synthesized by conventional method. except for the peaks at 1027 cm” and 673 cm-’ which are ascribed to the absorption of -SO$[ 1 S]. W-Vis absorption spectra of PANI-NSA microtubes in mcresol show two characteristic peaks at 430 nm and 900 nm with a long tail, which is consistent with PANI doped with CSA[IB]. It is interesting to find that two broad peaks centered at 28 = 15” and 30” with somesharp peaks at 28 = 8.8 O, 18.72 “, 19.94 ’ and 20.07 ’ were observed in the X-ray scattering patterns of PANI-NSA microtubes. It is resonable to believe that the first peak (at 28 = 15’) may be ascribed to the periodicity parallel to the polymer chain. whiIe the latter peaks. which are absent in the X-ray scattering pattern of PANI-HC1[20], may be caused by the periodicity perpendicular to the polymer chain. This indicates that the crystallinity of PANI-NSA microtubes is much higher than that of PANLHCI synthesized by conventional method. [21] In addition, the charateristic absorption bauds of PPy in the FTlR spectra, such as , the stretching vibration of C=C at 1565 cm-‘and 1619 cm-r, the vibration modes of the pyrrole riug at 1478 cm-’ and 1236 cm-i ~ and the in-plane and out-of-plane vibration modes of N-H and C-H at 1045, 968 and 922 cm‘1221, are observed in the FTIR spectra of PPy-NSA microtubes. Moreover, the R-X* absorption band at 43.5 nm and the polaron and bipolaron band at 646 and 97&n-’ in the UV-Vis absorption of PPy-NSA n&tubules are also observed[23]. Based on results mentioned above, the molecular structure of the PANI-NSA and PPy-NSA microtube by the new method is identical to that of the doped PAM and PPy synthesized by a conventional method.

It was found that the PPy-NSA minotubes are aoluhl~ ill In-cresol. and the soiubility increases with the iucreasr of tlu concentration of NSA. Moreover, the PANI-NSA nncrotuhrs can be soluble in tn-cresol. DMF and DMSO. The roonltemperature conductivity measured by a four-probr method is about 27 S/cm for PPy-NSA and 4.0 S/cm for PAh’I-NS.A microtubes respectively. Resuits obtained from ESR measurement and UV-Vis spectra proved that charge carrier is polaron for PANI-NSA. while both polaron and bipolaron fo: dependence of PPy-NSA microtubes. Temperaf ure conductivity for both PPy-NSA and PANI-XSA microtubes show semiconductor behavior. Temperature dep.endrnce of conductivity for PPy-NSA microtubes is best fittell 1)~ tiure dimentional variable rauge hoppiug (3DVRH) model. ~+hilr that of the PAW-NSA mictotubes can only be eq)resszd lr> lD-VRH model[24]as shown in Figure 3

T-lM(K-"4)

M. Wan

er al. / Synrhetic

Figure 3. Temperature dependence of conductivity for the PANI-NSA and PPy-NSA microtubes by the new method In conclusion: (1) a simple method termed as “in-situ doping polymerization” at the presence of NSA as dopant was used to synthesize PPy and PANI microtubes. The new method without template membrane and “molecular anchor”, might open a way to synthesize microtubes of conducting polymers. (2) The resulting PANI-NSA and PPy-NSA microtubes by the new method not only have high conductivity at room temperature (4-27 S/cm), but also are soluble in some organic solvents. (3) The molecular structures of the PANI-NSA and PPy-NSA microtubes are identical with that of PANI and PPy doped by a conventional method. (4) Polaron for PANI-NSA, both polaron and bipolaron for PPyNSA microtubuls as charge carriers are proved. Temperature dependence of conductivity for both PANI-NSA and PPy-NSA microtubes exhibites a semiconducting behavior, and it conforms to ID-VRH model for PANI-NSA and 3D-VRH model for PPy-NSA microtubes, respectively. 5. Acknowledgemeuts

This Project was supportedby the National Advanced Materials Committee of China, Fundation of Chinese Academy of Sciences,and ResearchFundationof Director of ChemistryInstitute, ChineseAcademyof Sciences. 6. References

[l]

A. S. Rudoldph,; J. M.Calvert,; P. E. Schoen, BiotechnologicalApplicationsof Lipid Microstructures;B. P. Caber; J. M. Schnur,ChapmanD: Plemum,New York 1988. [2] R. Pool, Science247(1990) 1410. [3] J.Tabony,D. Tob, Nature346(1990) 448 [4] H.Shirakawa, T.Iot, S. Ikeda, Makromol. Chem. 179 (1978) 1565. [5] W. S.Huang, B. O.Humphrey, MacDiarmid, A. G. J. Chem.Sot. FaradayTrans 82(1) (1986)2385.

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