In-situ polymerized polyaniline ®lms5.Brush-like chain orderingI.Sapurina a ,A.Yu.Osadchev a ,B.Z.V olchek a ,M.TrchovaÂb ,A.Riede c ,J.Stejskal d,*aInstitute of Macromolecular Compounds,Russian Academy of Sciences,St.Petersburg,199004,Russia bFaculty of Mathematics and Physics,Charles University Prague,18000Prague 8,Czech RepubliccFaculty of Physics and Earth Sciences,University of Leipzig,D-04103Leipzig,GermanydInstitute of Macromolecular Chemistry,Academy of Sciences of the Czech Republic,Heyrovsky Sq.2,16206Prague 6,Czech RepublicReceived 10December 2001;accepted 17January 2002AbstractThe polymerization conditions for preparation of ordered in-situ polymerized polyaniline (PANI)®lms were established.The thickness of ®lms deposited on glass can be controlled by the time spent in the reaction mixture and varied up to ca .250nm.The PANI chains initiated on the glass surface are expected to grow mostly perpendicularly to the support.The concept of brush-like ordering of PANI macromolecules in the ®lms is discussed on the basis of optical anisotropy measurements.The observed linear relation between ®lm thickness and molecular weight of PANI also supports the ordering hypothesis.The differences observed in absorption FTIR spectra of PANI ®lms and powders are discussed.#2002Elsevier Science B.V .All rights reserved.Keywords:Polyaniline;Conducting polymer;Thin ®lms;Polymer brush;Ordered structure;Optical anisotropy;FTIR spectra1.IntroductionAmong the conducting polymers,polyaniline (PANI)has been of particular interest because of its diverse structures,low cost,excellent environmental stability and wide appli-cations in different ®elds,such as microelectronics [1±4],corrosion protection of metals [5,6],sensors [7±9],electro-magnetic shielding [10],antistatic coatings [11],electrodes for batteries [12],catalysts [13],etc.A thin surface layer of PANI deposited on a suitable substrate is often needed for practical applications.Various techniques for the fabrication of well-de®ned thin PANI ®lms have been proposed.Elec-tropolymerization of aniline has often been used [14,15]but this method is restricted mainly to conducting surfaces,whereas no overlayer can be produced on insulating ones.The casting of a solution of PANI on the surface of a material,followed by evaporation of the solvent is another approach [16,17],especially when preparing thicker ®lms.There,the main obstacle is the insolubility of PANI in most of the solvents of practical interest.The Langmuir±Blodgettand self-assembling techniques have been also used to fabricate thin conducting ®lms [18±20].A commercially viable method still remains a challenge for future research.The chemical deposition of PANI,when the layer of polymer spontaneously forms on the surface of various materials immersed in the polymerization solution,is a promising alternative.In-situ polymerization is valuable for the preparation of ®lms on a variety of insulating and conducting,hydrophobic and hydrophilic surfaces [21].Only materials like iron,that are not stable in the acidic media used for the polymerization,are exceptions.Up to now,activity has been concentrated mainly on the broad-ening of the material range that can be used as the support for deposition.Various polymers,like polycarbonate,poly-(methyl methacrylate),polystyrene,as well as a variety of inorganic substrates,such as glass or ceramics,have suc-cessfully been tested.Only a limited number of papers have discussed the structural features of ®lms (thickness,surface morphology)and their physical properties (conductivity,optical absorption)in relation to the reaction conditions used in their preparation [22±25].Limited attention has been paid to studies of ®lm growth and of the internal structure of such ®lms [26].The present paper discusses the evolution of the ®lm structure during the polymerization ofaniline.Synthetic Metals 129(2002)29±37*Corresponding author.Tel.: 420-2-2040-3351;fax: 420-2-3535-7981.E-mail address:stejskal@imc.cas.cz (J.Stejskal).0379-6779/02/$±see front matter #2002Elsevier Science B.V .All rights reserved.PII:S 0379-6779(02)00036-X2.Model concept of film formationIt has frequently been observed that glass vessels used for the oxidation of aniline become coated with a thin PANI ®lm [22±29](Fig.1).There is,however,no de®nite answer to the question why these ®lms are produced at all.Such ®lms are not a result of a mere adhesion of precipitating PANI on glass surface.If glass supports are introduced into reaction mixture during progressing polymerization,no ®lm is pro-duced on them [26].The surfaces to be covered with a PANI ®lm thus,have to be in contact with reaction mixture from the beginning of aniline oxidation.Aniline cation radicals,as the primary products of aniline oxidation,are generated in the homogeneous aqueous med-ium.It is expected that the initiation step consists in the reaction of two cation radicals to form a dimer,p -amino-diphenylamine [30,31]that is able to be oxidized further to yield a PANI chain by the addition of aniline monomers.If aniline cation radicals adsorb at immersed surfaces,their ability to initiate chain growth may be increased.This may be caused by the induction effect ,i.e.by interaction with other cation radicals adsorbed in the neighbourhood.Alternatively,the adsorption at the surface alone may affect the electron structure of the adsorbed species and thus,their reactivity,as is well known in the heterogeneous catalysis of organic reactions by surfaces [32].Interaction between reac-tants in the presence of a solid catalyst is a common phenom-enon.These processes are catalyzed by the surface at which the reactions occur;in the absence of the solid,the reaction rate is generally very small.They are responsible for a decrease in the activation energy of reaction proceeding at the surface.In the present case,it is the enhanced reactivity of adsorbed aniline molecules or of adsorbed aniline cation radicals that leads to the easier initiation of PANI chains atthe surface.That is why the initiation and consequent for-mation of PANI proceeds preferentially at such surfaces and only later the similar process in the surrounding continuous phase follows [26,33].The rates of chain propagation at the surface and in the bulk are to be about the sameÐthe growing chains are hardly expected to remember the manner in which they were initiated.The overall rate of PANI formation thus should increase along with the surface available for the initiation of PANI chains.This simple conceptÐassuming the independent course of surface and bulk (precipitation)polymerizationsÐhelps to a better understanding of ®lm formation.A model of ®lm growth,leading to the brush-like orientation of PANI chains in the ®lms,has recently been proposed [26].It postulates that the adsorbed cation radicals initiate the growth of PANI chains and,because of steric reasons,the parallel orientation of macromolecules growing in the perpendicular direction to the support is anticipated [8,25,28,29].Experimental evi-dence supporting the orientation of macromolecules in the ®lms has been therefore sought in the present study.3.Experimental3.1.In-situ preparation of filmsThe PANI ®lms were produced on glass surfaces immersed in the reaction mixture during the oxidation of aniline.Aniline hydrochloride (0.2M)was oxidized in an aqueous medium with ammonium peroxydisulfate (0.25M)at room temperature.The progress of polymerization was monitored by temperature changes [34,35]recorded with a digital thermometer.The supports for the ®lms were either circular,13mm in diameter and of 1mm thickness,orFig.1.Profile of a PANI film deposited on glass,observed by scanning electron microscopy.Aniline hydrochloride (0.2M)was oxidized with ammonium peroxydisulfate (0.25M)at 208C.30I.Sapurina et al./Synthetic Metals 129(2002)29±37rectangular 25mm Â25mm Â0:5mm glasses.The latter supports were annealed for 20h at 5008C and then were left slowly to cool down prior to the coating.This procedure removed the optical anisotropy of the glass.The glasses were placed in the reaction mixture at the beginning of reaction and then removed at various stages of polymeriza-tion.The supports coated with PANI ®lm were rinsed with 0.2M HCl to remove the reactants and adhering PANI precipitate,then with acetone,and placed for 30min into 0.2M aniline hydrochloride solution.The quenching with a monomer solution converted an unstable pernigraniline intermediate to a stable emeraldine [22,36].The PANI ®lms deposited on supports were again washed with acetone and dried in air.A similar deposition technique was also used for the coating of silicon wafers for FTIR measurements.In one experiment,PANI was deposited on glass beads (Sigma,size 106m m and ®ner).The coated microspheres sediment well and could easily be separated from the PANI precipitate produced at the same time.The large surface of the micro-spheres facilitated the preparation of a suf®cient amount of PANI ®lm for use in gel-permeation-chromatography char-acterization,after the dissolution of deposited PANI.3.2.Characterization of filmsAbsorption spectra of the ®lms deposited on glass were recorded with a UV±VIS spectrometer Lambda 20(Perkin Elmer,UK)by using an uncoated glass as a reference.Film thickness was calculated from the relation between the ®lm thickness,d f ,determined by interferometry and optical absorption,A 400,at wavelength of 400nm,d f nm 185A 400,determined earlier [23].Optical anisotropy of PANI ®lms deposited on the isotropic glasses was characterized by using the experimental set-up shown in Fig.2.The vertically polarized light beam of wavelength l 0 633nm provided by a 90mW He±Ne laser (1)was converted to circularly polarized light with a l /4quartz plate (2)and then to a desired angle of polarization with a dielectric turmaline polarizer (3)with a work area of0.4±0.7m m.The beam passed through a glass support with a deposited PANI ®lm placed at 308angle (4)and its intensity was recorded with a linear photodiode (5)and a high-sensi-tivity electronic microamperemeter (6).The degree of polar-ization changed in 208steps.The transmittance of the PANI ®lm,T ,was calculated as the ratio of the light intensity passing through the support with the ®lm to the intensity passed through an uncoated glass.The experimental error of transmittance determination was 0.15%.FTIR transmittance measurements of ®lms deposited on silicon wafers were performed with a Bruker FT spectrometer IFS 113V .A two-layer model calculation was used to eliminate the in¯u-ence of the silicon support on the transmittance.Absorption FTIR spectra of the ®lms deposited on silicon were compared with those of PANI powders dispersed in KBr pellets by using a Nicolet IMPACT 400FTIR spectrometer in a water-purged environment.Coherent re¯ections in the silicon substrate were eliminated by decreasing the instrumental resolution to 8cm À1.An absorption subtraction technique was applied to remove the spectral features of the silicon wafers.Molar mass distribution of PANI dissolved in N -methyl-pyrrolidone containing 0.025g cm À3of triethanolamine (for the deprotonation of PANI),0.005g cm À3lithium bromide (to prevent aggregation)and 0.4vol.%benzene (as an internal standard)were assessed with a gel-permeation-chromatograph using 8mm Â500mm Labio GM 1000column calibrated with polystyrene standards [37].4.Results and discussion4.1.Polymerization of aniline at the surface and in the bulk The oxidation of aniline hydrochloride with ammonium peroxydisulfate in aqueous medium is a complex process [36],which can be summarized in a simple stoichiometric relation (Fig.3).The monitoring of polymerization by con-comitant spectral,temperature and acidity changes delimits two reaction phases [34,35,38±40].During theinductionFig.2.Set-up for the measurement of optical anisotropy.I.Sapurina et al./Synthetic Metals 129(2002)29±3731period,simple (and later oligomeric)aniline cation radicals are formed.The creation of cation radicals during the induction period plays decisive role in the future formation of ®lms.As we have recently shown [26],no ®lms are produced on supports inserted into the reaction mixture during the progressing polymerization in the bulk of the medium.A polymer produced at that stage has no ability to adsorb on the substrate.This proves that aniline cation radicals [26]or oligomeric intermediates [27]formed during the induction period adsorb on the immersed surfaces,and PANI chains subsequently grow from these primary nuclea-tion centers.During the consequent exothermic polymeriza-tion,PANI chains grow in oxidized pernigraniline form [22,36].The polymerization is supposed to proceed by a chain mechanism,because the molecular weight of PANI,as re¯ected by intrinsic viscosity,does not change signi®cantly as the conversion increases [41].It is important to realize that adsorption of active inter-mediates at the surface shortens the induction period.The polymerization then proceeds at the surface of immersed substrates independently of the similar process that follows later in the whole volume of the reaction mixture.We have shown [26]that the thickness of PANI ®lms increases as the surface polymerization proceeds.The polymerization at thesurface proceeds and PANI ®lms of about 10±20nm thick-ness are produced on the glass,even during the induction period in the bulk.The ®lm thickness further increases during the polymerization at 208C,typically to 180±250nm [23].Conducted in this way,in-situ polymerization is a suitable technique for the fabrication of well-de®ned thin ®lms;surface polymerization produces smooth ®lms.Poly-merization in the bulk is delayed but,as it starts,a PANI precipitate is produced in the aqueous phase.Because of that,the surface morphology of ®lm becomes granular in the ®nal stages of polymerization.The distinction between the surface polymerization and the precipitation polymerization of aniline is more pronounced at lower temperature,0±28C [33,42]and at low concentration of reactants [28].4.2.Film thickness and molar mass of polyaniline It has been noticed earlier [23],there is a proportionality between the ®lm thickness and molar mass of the produced PANI.This constitutes support for the model that predicts a brush-like ordering of chains in the ®lm.One can even make an attempt at a quantitative test of this hypothesis.The length of a segment comprising two aniline units in the conformation of a PANI chain was found,on the basis of X-ray diffraction results,to be l 1 0:96nm [43].Such a segment of PANI hydrochloride has a molar mass of M 1 217:66g mol À1.The ®lm thickness d f ,of a fully extended PANI macromolecule would be proportional to the number of segments,d f (l 1/M 1)M w where,M w is the weight-average molar mass.By using the ®lm thickness reported in the literature [23]and corresponding molar masses of PANI [37],a reasonably linear correlation is obtained (Fig.4).Some ®lms have a larger thickness than corresponds to a fully extended chain;this is probably due to the secondary nucleation of PANI chains onalreadyFig.3.Oxidation of aniline hydrochloride with ammonium peroxydisul-fate yields polyaniline (emeraldine)hydrochloride.Fig.4.Relation between film thickness,d f ,and weight-average molar mass of PANI chains,M w ,and comparison with the prediction of the thickness for the film composed by fully extended PANI chains,d f l 1=M 1 M w (full line).32I.Sapurina et al./Synthetic Metals 129(2002)29±37completed ®lm [26]and by the PANI precipitate adhering to the ®lm surface.A systematic error may have also been introduced into the gel-permeation-chromatography experi-ments that used polystyrene calibration for the calculation of PANI molecular masses [37].The discussion in the preceding paragraph is implicitly based on the assumption that the molar mass of PANI in ®lms produced by the surface polymerization and those in the PANI precipitate formed in the surrounding aqueous phase are identical.This is indeed con®rmed by the recent experimental observation that the gel-permeation chromatograms of PANI deposited as a ®lm on glass microspheres and of free PANI precipitate produced alongside are the same (Fig.5).This means that,although the initiation on the surface is enhanced compared with the homogeneous phase,the chain propaga-tion is the same,regardless of the locus of initiation.4.3.Ordering of the polymer chains as reflected by optical anisotropyThe dispersion of the optical density in an elliptically polarized beam of monochromic light was studied for eight ®lms of various thickness (Table 1).The dependence of the light transmission (relative to uncoated glass)on the angle of polarization for several samples is presented in Fig.6.The observed optical anisotropy correlates with anisotropy in molecular polarizability.It is thus possible to relate optical anisotropy with the orientation of macromolecules in a certain direction.The angular dependences are not symme-trical with respect to the 1808angle of polarization (Fig.6).This means that there are different parts of the ®lm with PANI molecules oriented in various directions.The structure of the ®lm may well be represented by a set of brushes having various spatial orientations and thus,deviating from the ideal brush produced in the perpendicular orientation to the support.The optical anisotropy was quantitatively assessed as a 2(T max ÀT min )/(T max T min ),where T max and T min are maximum and minimum transmittances observed for various angles of polarization [44].The anisotropy increases with growing ®lm thickness (Fig.7).This means that the macromolecules are locally organized in one direction with a high degree of orientation of their polariz-abilityvector.Fig.5.Weight distribution function of molar mass of PANI chains in the film produced on glass microspheres and in PANI precipitate produced simultaneously in the aqueous phase.The distribution functions obtained by GPC are vertically shifted for clarity.Table 1Optical,absorbance of polyaniline films A 400,at wavelength 400nm,the corresponding calculated film thickness,d f ,and the maximum transmittance,T max ,at an angle of polarization y max and minimum transmittance,T min ,at an angle y min at wavelength of 633nm,used for the calculation of optical anisotropy Polymerization time (min)A 400d f a (nm)T max y max (degree)T min y min (degree)10.080150.501760.49518920.102190.423800.41618230.184340.330720.32714540.469870.295760.27615650.6641230.190750.1771656 1.0972030.152930.1351837 1.1552140.132840.11017981.3602520.122790.100147aCalculated from the relation d f 185A 400based on interferometric calibration [23].I.Sapurina et al./Synthetic Metals 129(2002)29±37334.4.FTIR spectra of filmsWu et al.[25]have recently reported that PANI ®lms grown on silicon wafers display a set of ®ve peaks in absorption FTIR spectra that have not been observed in the spectra of PANI powder prepared under similar condi-tions.These,so-called ``H-peaks''[25],were assigned to the hydrogen bonding between regularly aligned PANI chains.We have also observed the development of these peaks during ®lm growth on a silicon wafer (Fig.8).The ®ve peaks are located at 3220,3140,3050,2920,and 2830cm À1,and approximately correspond to the wavenumbers reported by Wu et al.,3240,3154,3064,2975,and 2840cm À1[25].The position of peaks remains unchanged during ®lm for-mation and is thus,independent of ®lm thickness,as illu-strated,e.g.for the wavenumber 2920cm À1in Fig.8.The presence of peaks in the region 3300±2800cm À1has been con®rmed by independent preparation and FTIR character-ization in various authors'laboratories.The different spec-troscopic techniques used for variously prepared samples included the transmission measurements of ®lms deposited on silicon wafers,the attenuated total re¯ection applied to ®lms grown on polyethylene supports,and the re¯ection from ®lms prepared on gold mirrors [45].The absorption peaks remain unchanged even after heating ®lms deposited on silicon wafers to 1408C,during which deprotonation of the PANI ®lms has been observed [45].They are absent in the PANI hydrochloride powder prepared under the same conditions [25,45].There,they are replaced by a broad absorption band with a maximum at $3450cm À1also reported in the literature [25].It,thus,seems that the absorption bands in the region 3300±2800cm À1re¯ect the organization of PANI chains within the ®lm by hydrogen bonding involving NH and NH groups [25].It is known that the NH nitrogen stretching group has a diffuse band with lowered frequencies,and which may be composedofFig.6.Transmittance of PANI films of thickness,d f ,at wavelength 633nm,as a function of polarization angle.The dependences are vertically shifted for clarity of presentation.The experimental set-up is shown in Fig.2.Fig.7.Dependence of optical anisotropy on the film thickness.34I.Sapurina et al./Synthetic Metals 129(2002)29±37submaxima [46].In the case of strong hydrogen bonds,the NH stretching band may,in some cases,be composed of equidistant submaxima [46].The repetition spacing in the ®ne structure in the NH stretching band (about 90cm À1observed in the ®lms of PANI hydrochloride)may be explained by interaction with very low frequency deforma-tions of hydrogen bonds [47].The part of spectrum <2000cm À1shows some notable differences for protonated PANI ®lms on silicon substrates and PANI powders dispersed in KBr pellets (Fig.9).These are observed especially in the positions of the main peaks at 1590and 1500cm À1,corresponding to quinone and benzene stretching ring-deformation.The shape of the absorption band at 1308cm À1(C±N stretching of secondary aromatic amine strengthened during the protonation of PANI)has also been changed.The band characteristic of the conducting protonated form,observed at about 1240cm À1in protonated PANI and interpreted as C±N stretching vibration in the polaron structure [48],is shifted too.The 1140cm À1band,assigned to a vibration mode of the ÀNH structure,produced by protonation [49],changed its pro®le.These changes have been con®rmed by independent preparation of PANI samples and FTIR measurements in various labora-tories of the authors.They are also visible in thespectraFig.8.Evolution of FTIR absorption spectra for PANI films deposited on silicon wafers during the polymerization of aniline after various reaction times,t (min).The ``H-peaks''are well seen in the area delimited by dashed lines.Aniline hydrochloride (0.2M)was oxidized with ammonium peroxydisulfate (0.2M)at 08C.Fig.9.FTIR spectra of PANI (emeraldine)hydrochloride obtained in transmission mode on powder dispersed in a KBr pellet and on film deposited in situ on a silicon wafer.I.Sapurina et al./Synthetic Metals 129(2002)29±3735reported by Wu et al.[25],although they were not discussed by those authors.The differences between the spectra of the ®lm and of the powder disappeared after deprotonation of PANI hydrochloride to PANI base.It is known that the different sampling methods yield spectra that differ in the frequency,shape,and intensity of the bands[50].The magnitude of the signal that is either re¯ected or transmitted is determined by the relative optical constants of the two phases and by the angle of incidence.In the transmission mode,the major contribution comes from the so-called absorptive index while the refractive index contribution is small.In re¯ection measurements,the major contributor is the refractive index.The metallic character of protonated PANI ampli®es the in¯uence of re¯ections and scattering on the spectra that disappears after deprotonation of PANI to a non-conducting state.The in¯uence of different organiza-tion of chains on this part of FTIR spectra can be ruled out on the basis of the identity of the spectra of the®lm and powder forms of PANI base.5.ConclusionsPANI®lms were produced in situ on glass and on silicon during the oxidation of aniline.The model of®lm formation assumes that aniline cation radicals adsorb at the surfaces immersed in the reaction mixture and,as a result of hetero-geneous catalysis by surface or because of mutual interac-tion,they initiate the preferential growth of PANI chains. The PANI macromolecules are therefore,expected to be oriented in the®lm in the direction perpendicular to the surface.This concept is supported by the observation that the ®lm thickness is proportional to the molar mass of the PANI chains.The measurement of the optical anisotropy of the ®lms establishes the orientation of chains in the®lms.The FTIR spectra exhibit several absorption peaks in the region of3300±2800cmÀ1that are connected with the organization of PANI chains in the®lm;these are absent in the spectra of PANI powders.Differences between the spectra of proto-nated PANI®lms and powders are also observed at wave-numbers<2000cmÀ1.They re¯ect the in¯uence of the metallic character of these two conducting PANI forms on the spectra obtained by different methods.AcknowledgementsAuthors wish to thank the Ecros company,St.Petersburg, the Grant Agency of the Czech Republic(202/02/0698)and the Academy of Sciences(K4050111)for®nancial support.References[1]S.-A.Chen,K.-R.Chuang,C.-I.Chao,H.-T.Lee,Synth.Met.82(1996)207.[2]P.Topart,P.Hourquebie,Thin Solid Films352(1999)243.[3]W.Feng,E.Sun,A.Fujii,H.Wu,K.Niihara,K.Yoshino,Bull.Chem.Soc.Jpn.73(2000)2627.[4]A.G.MacDiarmid,Angew.Chem.Int.Ed.40(2001)2581.[5]W.-K.Lu,S.Basak,R.L.Elsenbaumer,in:T.A.Skotheim,R.L.Elsenbaumer,J.R.Reynolds(Eds.),Handbook of Conducting Polymers,2nd edition,Dekker,New York,1998(Chapter31) pp.881±920.[6]R.Gasparac,C.R.Martin,J.Electrochem.Soc.148(2001)B138.[7]G.Bidan,Sens.Actuators B6(1992)45.[8]S.Sukeerthi,A.Q.Contractor,Chem.Mater.10(1998)2412.[9]M.E.Nicho,M.Trejo, A.GarcõÂa-Valenzuela,J.M.Saniger,J.Palacios,H.Hu,Sens.Actuators B76(2001)18.[10]J.Joo,A.J.Epstein,Appl.Phys.Lett.65(1994)2278.[11]D.C.Trivedi,S.K.Dhavan,J.Mater.Chem.2(1992)1091.[12]J.Y.Lee,L.H.Ong,G.K.Chuah,J.Appl.Electrochem.22(1992)738.[13]S.Kuwabata,N.Takahashi,S.Hirao,H.Yoneyama,Chem.Mater.5(1993)437.[14]H.Okamoto,T.Kotaka,Polymer40(1999)407.[15]D.C.Trivedi,in:H.S.Nalwa(Ed.),Handbook of Organic ConductiveMolecules and Polymers,V ol2,Wiley,Chichester,1997,pp.510±517.[16]Y.Cao,P.Smith,A.J.Heeger,Synth.Met.48(1992)91.[17]R.V.Gregory,in:T.A.Skotheim,R.L.Elsenbaumer,J.R.Reynolds(Eds.),Handbook of Conducting Polymers,2nd edition,Dekker, New York,1998,pp.437±466.[18]J.H.Cheung,A.F.Fou,M.F.Rubner,Thin Solid Films244(1994)985.[19]W.M.Stockton,M.F.Rubner,Macromolecules30(1997)2717.[20]D.Li,Y.Jiang,Z.Wu,X.Chen,Y.Li,Thin Solid Films360(2000)24.[21]A.Malinauskas,Polymer42(2001)3957.[22]J.K.Avlyanov,J.Y.Josefowicz,A.G.MacDiarmid,Synth.Met.73(1995)205.[23]J.Stejskal,I.Sapurina,J.ProkesÏ,J.Zemek,Synth.Met.105(1999)195.[24]L.A.P.Kane-Maguire,A.G.MacDiarmid,I.D.Norris,G.G.Wallace,W.Zheng,Synth.Met.106(1999)171.[25]C.-G.Wu,Y.-R.Yeh,J.-Y.Chen,Y.-H.Chiou,Polymer42(2001)2877.[26]I.Sapurina,A.Riede,J.Stejskal,Synth.Met.123(2001)503.[27]A.G.MacDiarmid,Synth.Met.84(1997)27.[28]H.H.Kuhn,A.D.Child,in:T.A.Skotheim,R.L.Elsenbaumer,J.R.Reynolds(Eds.),Handbook of Conducting Polymers,2nd edition, Dekker,New York,1998(Chapter35)pp.993±1013.[29]C.R.Martin,in:T.A.Skotheim,R.L.Elsenbaumer,J.R.Reynolds(Eds.),Handbook of Conducting Polymers,2nd edition,Dekker, New York,1998(Chapter16)pp.409±421.[30]F.Cases,F.Huerta,P.GarceÂs,R.MoralloÂn,J.L.VazqueÂz,J.Electroanal.Chem.501(2001)186.[31]N.Gospodinova,L.Terlemezyan,Prog.Polym.Sci.23(1998)1443.[32]P.W.Atkins,Physical Chemistry,3rd edition,Oxford UniversityPress,Oxford,1986(Chapter31)pp.762±789.[33]A.V.Orlov,V.G.Kiseleva,O.Y.Yurchenko,G.P.Karpacheva,Polym.Sci.A42(2000)1292.[34]Y.Fu,R.L.Elsenbaumer,Chem.Mater.6(1994)671.[35]T.Sulimenko,J.Stejskal,I.KrÏivka,J.ProkesÏ,Eur.Polym.J.37(2001)219.[36]J.Stejskal,P.KratochvõÂl,A.D.Jenkins,Polymer37(1996)367.[37]J.Stejskal,A.Riede,D.HlavataÂ,J.ProkesÏ,M.Helmstedt,P.Holler,Synth.Met.96(1998)55.[38]P.M.Beadle,Y.F.Nicolau,E.Banka,P.Rannou,D.Djurado,Synth.Met.95(1998)29.[39]N.Gospodinova,L.Terlemezyan,P.Mokreva,A.Tadjer,Polymer37(1996)4431.[40]M.Chakraborthy,D.C.Mukerjee,B.M.Mandal,Langmuir16(2000)2482.36I.Sapurina et al./Synthetic Metals129(2002)29±37。
