Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature
Identifieur interne : 001349 ( Istex/Corpus ); précédent : 001348; suivant : 001350Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature
Auteurs : Nadra Bohli ; Fethi Gmati ; Abdellatif Belhadj Mohamed ; Valrie Vigneras ; Jean-Louis MianeSource :
- Journal of Physics D: Applied Physics [ 0022-3727 ] ; 2009.
Abstract
In this work, we report a study of the effect of the solvent type and the casting temperature on the electrical properties of pure fully doped conducting polymer films (polyaniline, PANI). PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAAFA)). Previous work showed that at around 318K, a second order liquidliquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 room temperature, 318 and 353K). The electrical properties of the cast films were investigated in the frequency range 100Hz1MHz. The temperature was varied between 20 and 300K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAAFA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.
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DOI: 10.1088/0022-3727/42/20/205404
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Gmati</name><affiliation><mods:affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</mods:affiliation></affiliation></author><author><name sortKey="Mohamed, Abdellatif Belhadj" sort="Mohamed, Abdellatif Belhadj" uniqKey="Mohamed A" first="Abdellatif Belhadj" last="Mohamed">Abdellatif Belhadj Mohamed</name><affiliation><mods:affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</mods:affiliation></affiliation></author><author><name sortKey="Vigneras, Valrie" sort="Vigneras, Valrie" uniqKey="Vigneras V" first="Valrie" last="Vigneras">Valrie Vigneras</name><affiliation><mods:affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</mods:affiliation></affiliation></author><author><name sortKey="Miane, Jean Louis" sort="Miane, Jean Louis" uniqKey="Miane J" first="Jean-Louis" last="Miane">Jean-Louis Miane</name><affiliation><mods:affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:5321363D38B206309A5FCB2F8D22724D94B58756</idno><date when="2009" year="2009">2009</date><idno type="doi">10.1088/0022-3727/42/20/205404</idno><idno type="url">https://api.istex.fr/document/5321363D38B206309A5FCB2F8D22724D94B58756/fulltext/pdf</idno><idno type="wicri:Area/Istex/Corpus">001349</idno><idno type="wicri:explorRef" wicri:stream="Istex" wicri:step="Corpus" wicri:corpus="ISTEX">001349</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a" type="main" xml:lang="en">Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</title><author><name sortKey="Bohli, Nadra" sort="Bohli, Nadra" uniqKey="Bohli N" first="Nadra" last="Bohli">Nadra Bohli</name><affiliation><mods:affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</mods:affiliation></affiliation><affiliation><mods:affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: nadra.bohli@crten.rnrt.tn</mods:affiliation></affiliation></author><author><name sortKey="Gmati, Fethi" sort="Gmati, Fethi" uniqKey="Gmati F" first="Fethi" last="Gmati">Fethi Gmati</name><affiliation><mods:affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</mods:affiliation></affiliation></author><author><name sortKey="Mohamed, Abdellatif Belhadj" sort="Mohamed, Abdellatif Belhadj" uniqKey="Mohamed A" first="Abdellatif Belhadj" last="Mohamed">Abdellatif Belhadj Mohamed</name><affiliation><mods:affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</mods:affiliation></affiliation></author><author><name sortKey="Vigneras, Valrie" sort="Vigneras, Valrie" uniqKey="Vigneras V" first="Valrie" last="Vigneras">Valrie Vigneras</name><affiliation><mods:affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</mods:affiliation></affiliation></author><author><name sortKey="Miane, Jean Louis" sort="Miane, Jean Louis" uniqKey="Miane J" first="Jean-Louis" last="Miane">Jean-Louis Miane</name><affiliation><mods:affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Journal of Physics D: Applied Physics</title><title level="j" type="abbrev">J. Phys. D: Appl. Phys.</title><idno type="ISSN">0022-3727</idno><idno type="eISSN">1361-6463</idno><imprint><publisher>IOP Publishing</publisher><date type="published" when="2009">2009</date><biblScope unit="volume">42</biblScope><biblScope unit="issue">20</biblScope><biblScope unit="page" from="1">1</biblScope><biblScope unit="page" to="7">7</biblScope><biblScope unit="production">Printed in the UK</biblScope></imprint><idno type="ISSN">0022-3727</idno></series><idno type="istex">5321363D38B206309A5FCB2F8D22724D94B58756</idno><idno type="DOI">10.1088/0022-3727/42/20/205404</idno><idno type="PII">S0022-3727(09)21180-6</idno><idno type="articleID">321180</idno><idno type="articleNumber">205404</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0022-3727</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract">In this work, we report a study of the effect of the solvent type and the casting temperature on the electrical properties of pure fully doped conducting polymer films (polyaniline, PANI). PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAAFA)). Previous work showed that at around 318K, a second order liquidliquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 room temperature, 318 and 353K). The electrical properties of the cast films were investigated in the frequency range 100Hz1MHz. The temperature was varied between 20 and 300K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAAFA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.</div></front></TEI><istex><corpusName>iop</corpusName><author><json:item><name>Nadra Bohli</name><affiliations><json:string>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</json:string><json:string>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</json:string><json:string>E-mail: nadra.bohli@crten.rnrt.tn</json:string></affiliations></json:item><json:item><name>Fethi Gmati</name><affiliations><json:string>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</json:string></affiliations></json:item><json:item><name>Abdellatif Belhadj Mohamed</name><affiliations><json:string>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</json:string></affiliations></json:item><json:item><name>Valrie Vigneras</name><affiliations><json:string>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</json:string></affiliations></json:item><json:item><name>Jean-Louis Miane</name><affiliations><json:string>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</json:string></affiliations></json:item></author><subject><json:item><lang><json:string>eng</json:string></lang><value>Conductivity mechanism</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>conducting polymer</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>processing parameters</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>structure</value></json:item></subject><language><json:string>eng</json:string></language><originalGenre><json:string>paper</json:string></originalGenre><abstract>In this work, we report a study of the effect of the solvent type and the casting temperature on the electrical properties of pure fully doped conducting polymer films (polyaniline, PANI). PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAAFA)). Previous work showed that at around 318K, a second order liquidliquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 room temperature, 318 and 353K). The electrical properties of the cast films were investigated in the frequency range 100Hz1MHz. The temperature was varied between 20 and 300K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAAFA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.</abstract><qualityIndicators><score>6.079</score><pdfVersion>1.4</pdfVersion><pdfPageSize>595 x 841 pts</pdfPageSize><refBibsNative>true</refBibsNative><keywordCount>4</keywordCount><abstractCharCount>1262</abstractCharCount><pdfWordCount>3359</pdfWordCount><pdfCharCount>18436</pdfCharCount><pdfPageCount>7</pdfPageCount><abstractWordCount>185</abstractWordCount></qualityIndicators><title>Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</title><pii><json:string>S0022-3727(09)21180-6</json:string></pii><genre><json:string>research-article</json:string></genre><host><volume>42</volume><publisherId><json:string>jphysd</json:string></publisherId><pages><total>7</total><last>7</last><first>1</first></pages><issn><json:string>0022-3727</json:string></issn><issue>20</issue><genre><json:string>journal</json:string></genre><language><json:string>unknown</json:string></language><eissn><json:string>1361-6463</json:string></eissn><title>Journal of Physics D: Applied Physics</title></host><publicationDate>2009</publicationDate><copyrightDate>2009</copyrightDate><doi><json:string>10.1088/0022-3727/42/20/205404</json:string></doi><id>5321363D38B206309A5FCB2F8D22724D94B58756</id><score>0.04148542</score><fulltext><json:item><original>true</original><mimetype>application/pdf</mimetype><extension>pdf</extension><uri>https://api.istex.fr/document/5321363D38B206309A5FCB2F8D22724D94B58756/fulltext/pdf</uri></json:item><json:item><original>false</original><mimetype>application/zip</mimetype><extension>zip</extension><uri>https://api.istex.fr/document/5321363D38B206309A5FCB2F8D22724D94B58756/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/5321363D38B206309A5FCB2F8D22724D94B58756/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a" type="main" xml:lang="en">Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>IOP Publishing</publisher><availability><p>2009 IOP Publishing Ltd</p></availability><date>2009</date></publicationStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a" type="main" xml:lang="en">Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</title><author xml:id="author-1"><persName><forename type="first">Nadra</forename><surname>Bohli</surname></persName><email>nadra.bohli@crten.rnrt.tn</email><affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</affiliation><affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</affiliation></author><author xml:id="author-2"><persName><forename type="first">Fethi</forename><surname>Gmati</surname></persName><affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</affiliation></author><author xml:id="author-3"><persName><forename type="first">Abdellatif Belhadj</forename><surname>Mohamed</surname></persName><affiliation>Laboratoire de Nanomatriaux et des Systmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria, BP 95 Hammam Lif 2050, Tunisia</affiliation></author><author xml:id="author-4"><persName><forename type="first">Valrie</forename><surname>Vigneras</surname></persName><affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</affiliation></author><author xml:id="author-5"><persName><forename type="first">Jean-Louis</forename><surname>Miane</surname></persName><affiliation>Laboratoire de l'Intgration du Matriau au Systme, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, France</affiliation></author></analytic><monogr><title level="j">Journal of Physics D: Applied Physics</title><title level="j" type="abbrev">J. Phys. D: Appl. Phys.</title><idno type="pISSN">0022-3727</idno><idno type="eISSN">1361-6463</idno><imprint><publisher>IOP Publishing</publisher><date type="published" when="2009"></date><biblScope unit="volume">42</biblScope><biblScope unit="issue">20</biblScope><biblScope unit="page" from="1">1</biblScope><biblScope unit="page" to="7">7</biblScope><biblScope unit="production">Printed in the UK</biblScope></imprint></monogr><idno type="istex">5321363D38B206309A5FCB2F8D22724D94B58756</idno><idno type="DOI">10.1088/0022-3727/42/20/205404</idno><idno type="PII">S0022-3727(09)21180-6</idno><idno type="articleID">321180</idno><idno type="articleNumber">205404</idno></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2009</date></creation><langUsage><language ident="en">en</language></langUsage><abstract><p>In this work, we report a study of the effect of the solvent type and the casting temperature on the electrical properties of pure fully doped conducting polymer films (polyaniline, PANI). PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAAFA)). Previous work showed that at around 318K, a second order liquidliquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 room temperature, 318 and 353K). The electrical properties of the cast films were investigated in the frequency range 100Hz1MHz. The temperature was varied between 20 and 300K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAAFA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.</p></abstract><textClass><keywords scheme="keyword"><list><head>keywords</head><item><term>Conductivity mechanism</term></item><item><term>conducting polymer</term></item><item><term>processing parameters</term></item><item><term>structure</term></item></list></keywords></textClass><textClass><classCode scheme="">72.80.r</classCode></textClass></profileDesc><revisionDesc><change when="2009">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><original>false</original><mimetype>text/plain</mimetype><extension>txt</extension><uri>https://api.istex.fr/document/5321363D38B206309A5FCB2F8D22724D94B58756/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus iop not found" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="ISO-8859-1"</istex:xmlDeclaration><istex:docType SYSTEM="http://ej.iop.org/dtd/iopv1_5_2.dtd" name="istex:docType"></istex:docType><istex:document><article artid="jphysd321180"><article-metadata><jnl-data jnlid="jphysd"><jnl-fullname>Journal of Physics D: Applied Physics</jnl-fullname><jnl-abbreviation>J. Phys. D: Appl. Phys.</jnl-abbreviation><jnl-shortname>JPhysD</jnl-shortname><jnl-issn>0022-3727</jnl-issn><jnl-coden>JPAPBE</jnl-coden><jnl-imprint>IOP Publishing</jnl-imprint><jnl-web-address>stacks.iop.org/JPhysD</jnl-web-address></jnl-data><volume-data><year-publication>2009</year-publication><volume-number>42</volume-number></volume-data><issue-data><issue-number>20</issue-number><coverdate>21 October 2009</coverdate></issue-data><article-data><article-type type="paper" sort="regular"></article-type><type-number type="paper" numbering="article" artnum="205404"></type-number><article-number>321180</article-number><first-page>1</first-page><last-page>7</last-page><length>7</length><pii>S0022-3727(09)21180-6</pii><doi>10.1088/0022-3727/42/20/205404</doi><copyright>2009 IOP Publishing Ltd</copyright><ccc>0022-3727/09/205404+07$30.00</ccc><printed>Printed in the UK</printed><features colour="global" mmedia="no" suppdata="no"></features></article-data></article-metadata><header><title-group><title>Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</title><short-title>Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</short-title><ej-title>Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature</ej-title></title-group><author-group><author address="jphysd321180ad1 jphysd321180ad2" email="jphysd321180ea1"><first-names>Nadra</first-names><second-name>Bohli</second-name></author><author address="jphysd321180ad1"><first-names>Fethi</first-names><second-name>Gmati</second-name></author><author address="jphysd321180ad1"><first-names>Abdellatif Belhadj</first-names><second-name>Mohamed</second-name></author><author address="jphysd321180ad2"><first-names>Valérie</first-names><second-name>Vigneras</second-name></author><author address="jphysd321180ad2"><first-names>Jean-Louis</first-names><second-name>Miane</second-name></author></author-group><address-group><address id="jphysd321180ad1"><orgname>Laboratoire de Nanomatériaux et des Systèmes pour l'Energie, Centre de Recherches et de Technologies de l'Energie, Technopole de Borj Cedria</orgname>, BP 95 Hammam Lif 2050, <country>Tunisia</country></address><address id="jphysd321180ad2"><orgname>Laboratoire de l'Intégration du Matériau au Système</orgname>, UMR CNRS 5218, ENSCPB, 16, Avenue Pey Berland, 33607 Pessac, <country>France</country></address><e-address id="jphysd321180ea1"><email mailto="nadra.bohli@crten.rnrt.tn">nadra.bohli@crten.rnrt.tn</email></e-address></address-group><history received="10 June 2009" finalform="18 August 2009" online="24 September 2009"></history><abstract-group><abstract><heading>Abstract</heading><p indent="no">In this work, we report a study of the effect of the solvent type and the casting temperature on the electrical properties of pure fully doped conducting polymer films (polyaniline, PANI). PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAA–FA)). Previous work showed that at around 318 K, a second order liquid–liquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 ‘room temperature’, 318 and 353 K). The electrical properties of the cast films were investigated in the frequency range 100 Hz–1 MHz. The temperature was varied between 20 and 300 K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAA–FA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.</p></abstract></abstract-group><classifications><class-codes scheme="pacs" print="no"><code>72.80.r</code></class-codes><keywords print="no"><keyword>Conductivity mechanism</keyword><keyword>conducting polymer</keyword><keyword>processing parameters</keyword><keyword>structure</keyword></keywords></classifications></header><body numbering="bysection"><sec-level1 id="jphysd321180s1" label="1"><heading>Introduction</heading><p indent="no">Intrinsically conducting polymers in general, and polyaniline (PANI) in particular, are an interesting class of materials as they offer chemical stability, ease of synthesis [<cite linkend="jphysd321180bib01">1</cite>] and low cost compared with inorganic semiconductors. These polymers have wide applications such as in solar cells, lightweight batteries, light emitting diodes, polymer corrosion protection agents, sensors and molecular electronic devices. However, such commercial applications are limited for PANI because of its poor processability and intractable nature.</p><p>Many attempts have been made to enhance the processability of PANI especially using plastdopants [<cite linkend="jphysd321180bib02">2</cite>]. Plastdoped PANI dispersed in dichloroacetic acid (DCAA) is a material capable of giving good performances in terms of conductivity and mechanical properties. However, its viscosity is so high that it is difficult to process films from these types of dispersions. In order to improve the processability of these PANI films, formic acid (FA) can be added (to decrease the viscosity of the dispersion). Previous work done on dispersions of fully doped PANI in two different solvents (pure DCAA and a mixture DCAA–FA) revealed the existence of a second order liquid–liquid structural transition appearing on heating at a temperature of 318 K [<cite linkend="jphysd321180bib03">3</cite>]. This transition induced changes in the dielectric and rheological properties of the dispersions.</p><p>With the aim of finding the adequate processing parameters leading to films with the best conductivity, we wanted to investigate how the dispersion state can influence the final electrical conductivity of the plastdoped PANI films (memory effect), and to see whether the morphological changes occurring at that transition temperature last along the casting process or lose their effect. Consequently, we have investigated the electrical conductivity and the structural properties of PANI films cast from two different organic solvents at three temperatures: around the transition temperature (318 K), the room temperature (298 K) and a quite high temperature (353 K).</p></sec-level1><sec-level1 id="jphysd321180s2" label="2"><heading>Experimental techniques</heading><sec-level2 id="jphysd321180s2-1" label="2.1"><heading>Samples preparation</heading><p indent="no">Plastdoped PANI dispersed in two different solvents, DCAA and a mixture containing 20% in volume of FA and 80% in volume of dichloroacetic acid (DCAA–FA), was obtained from PANIPLAST (France). The dispersions were magnetically stirred for 24 h. The weight percentage of PANI was 5% in DCAA and 4% in DCAA–FA. Each dispersion was cooled onto a glass substrate and dried in an oven for 3 h at three different temperatures: 298, 318 and 353 K. The film thickness was estimated using scanning electron microscopy (SEM) observation. It varied between 4 and 14 µm.</p></sec-level2><sec-level2 id="jphysd321180s2-2" label="2.2"><heading>X-ray diffraction</heading><p indent="no">X-ray diffractions were carried out on the films using an Analytical X'pert Pro MPD diffractometer with the cobalt radiation λ = 1.789 Å, in the 2&thetas; range 5°–70° in steps of 0.017°.</p></sec-level2><sec-level2 id="jphysd321180s2-3" label="2.3"><heading>Impedance measurements</heading><p indent="no">Real and imaginary parts of complex impedance, <italic>Z</italic>(ω) = <italic>Z′</italic>(ω) + j<italic>Z</italic>″(ω), were measured between 100 Hz and 1 MHz using an HP 4192A Impedance Analyzer. We have made coplanar electrical contacts by depositing parallel metal electrodes on the film surface. The system is considered as a plane capacitor and described by a parallel RC circuit [<cite linkend="jphysd321180bib04">4</cite>, <cite linkend="jphysd321180bib05">5</cite>]. Then, we put the film on a refrigerating bath in vacuum in order to perform measurements in the temperature range 20–300 K. The temperature was controlled by a Lakeshore 331 heater controller.</p><p>We denote by ϵ<sup>*</sup>(ω) = ϵ′(ω) − jϵ″(ω) the generalized complex dielectric permittivity where ϵ″(ω) describes the global loss factor in the material. The permittivity ϵ<sup>*</sup>(ω) and the conductivity σ(ω) were determined from impedance data by employing the following relations [<cite linkend="jphysd321180bib06">6</cite>]:
<display-eqn id="jphysd321180eq001" eqnnum="1"></display-eqn><display-eqn id="jphysd321180eq002" eqnnum="2"></display-eqn><display-eqn id="jphysd321180eq003" eqnnum="3"></display-eqn>
where <italic>C</italic><sub>0</sub> is the capacity with a free space between the electrodes, <italic>t</italic> is the thickness of the film and <italic>l</italic> the length of an electrode and <italic>L</italic> is the width between the two electrodes, ϵ<sub>0</sub> the permittivity of vacuum and ω the angular frequency of the applied electric field.</p></sec-level2></sec-level1><sec-level1 id="jphysd321180s3" label="3"><heading>Results and discussion</heading><sec-level2 id="jphysd321180s3-1" label="3.1"><heading>X-ray diffraction analysis</heading><p indent="no">We present in figure <figref linkend="jphysd321180fig01">1</figref> the x-ray diffraction patterns recorded for the PANI/DCAA and PANI/DCAA–FA films dried at three different temperatures, 298, 318 and 353 K. We note the semi-crystalline structure of the PANI/DCAA film (<italic>T</italic> = 298 K) characterized by the presence of diffraction peaks at 2&thetas; = 23.5° and 2&thetas; = 31.5°. This indicates a semi-crystalline structure formed by well-ordered regions embedded in an amorphous medium [<cite linkend="jphysd321180bib07">7</cite>]. For the PANI/DCAA–FA cast films, the x-ray patterns show a rather amorphous structure. The difference between the two x-ray patterns is indicative of the influence of the solvent on the final morphology of the films.
<figure id="jphysd321180fig01" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/jphysd321180fig01.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/jphysd321180fig01.jpg"></graphic-file></graphic><caption id="jphysd321180fc01" label="Figure 1"><p indent="no">The x-ray patterns of the PANI films cast from (<italic>a</italic>) DCAA solvent and (<italic>b</italic>) DCAA–FA solvent and dried at 298 K, 318 K and 353 K.</p></caption></figure></p></sec-level2><sec-level2 id="jphysd321180s3-2" label="3.2"><heading>Morphological analyses</heading><p indent="no">The SEM micrographs of PANI cast from DCAA solvent and DCAA–FA solvent and dried at 298, 318 and 353 K are shown in figure <figref linkend="jphysd321180fig02">2</figref>. The effect of the solvent used and the casting temperature can be observed through the surface morphology change. For instance, the morphology of the films cast at 353 K seems to be different compared with the others (figure <figref linkend="jphysd321180fig02">2</figref>). It shows a sponge-like structure (porous). In fact, at such a high temperature the solvent is released from the film surface quite rapidly, so that the PANI chains do not have enough time to take its place. The granular morphology shown in the other figures can be attributed to the PANI crystalline clusters embedded in the amorphous PANI matrix.
<figure id="jphysd321180fig02" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/jphysd321180fig02.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/jphysd321180fig02.jpg"></graphic-file></graphic><caption id="jphysd321180fc02" label="Figure 2"><p indent="no">Scanning electron micrographs of the PANI films cast from DCAA solvent dried at (<italic>a</italic>) 298 K, (<italic>b</italic>) 318 K and (<italic>c</italic>) 353 K and for DCAA–FA solvent and dried at (<italic>d</italic>): 298 K, (<italic>e</italic>) 318 K and (<italic>f</italic>) 353 K.</p></caption></figure></p></sec-level2><sec-level2 id="jphysd321180s3-3" label="3.3"><heading>Conductivity studies</heading><p indent="no">The variation of the total conductivity of the intrinsically conducting polymers with frequency and temperature is generally described by the Jonscher law [<cite linkend="jphysd321180bib08">8</cite>]:
<display-eqn id="jphysd321180ueq001"></display-eqn>
The conductivity maintains a constant value (σ<sub>dc</sub>) over a certain range of frequencies (low frequencies). Up to a certain frequency, it begins to monotonically increase as a power law term is added (alternate frequency conductivity). This behaviour was not observed for our samples as the frequency window was not sufficiently wide to observe it. In fact, when we observe the conductivity of a PANI/DCAA film at 295 K (the film was cast at 298 K), as shown in figure <figref linkend="jphysd321180fig03">3</figref>, we note that it is almost constant over the whole range of frequency. This behaviour is observed for all our samples. So, to determine σ<sub>dc</sub>, we extrapolated the data recorded at the low frequency to the static frequency (ω = 0).
<figure id="jphysd321180fig03" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/jphysd321180fig03.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/jphysd321180fig03.jpg"></graphic-file></graphic><caption id="jphysd321180fc03" label="Figure 3"><p indent="no">Variation of conductivity with frequency for a PANI/DCAA film at 295 K (the film was cast at 298 K).</p></caption></figure></p><p>The conduction mechanism in PANI is complex and no single model can represent it. In fact, PANI can be generally assimilated to metallic islands surrounded by amorphous regions, in which electronic wavefunctions are localized in the amorphous region, and delocalized in the metallic regions. Moreover, synthesis and processing parameters, such as the nature of the dopant used, can affect the degree of disorder existing in the PANI system (size of the metallic regions, inter-metallic regions distance, etc).</p><p>Several models, similar to the models developed for amorphous semiconductors [<cite linkend="jphysd321180bib09">9</cite>], have been proposed to explain the charge transport process in organic semiconductors in general and PANI in particular such as the hopping to the nearest neighbouring states (HNN), Mott's variable range hopping (VRH), the charging energy limited tunnelling (CELT) or the fluctuation induced tunnelling (FIT).</p><p>The HNN is generally observed in the case of strong localization. The hopping conductivity is depicted as
<display-eqn id="jphysd321180eq004" eqnnum="4"></display-eqn>
where σ<sub>0</sub> is a constant and <italic>W</italic> is called the activation energy required for a charge carrier to hop from one site to another.</p><p>The CELT model generally applies [<cite linkend="jphysd321180bib10" range="bib10,bib11,bib12">10–12</cite>] to the low conductivity conjugated polymers. This model is consistent with the picture of a material with a heterogeneous structure of the granular metal type:
<display-eqn id="jphysd321180eq005" eqnnum="5"></display-eqn>
where σ<sub>0</sub> is a pre-exponential factor and <italic>T</italic><sub>0</sub> is a constant which, when multiplied by Boltzmann's constant, results in the activation energy of the dc conductivity.</p><p>In the case of weak localization, a charge carrier can jump not to a neighbour, but energetically favourable states. The transport then occurs by Mott's model [<cite linkend="jphysd321180bib09">9</cite>, <cite linkend="jphysd321180bib13" range="bib13,bib14,bib15">13–15</cite>] based on 3D fixed (γ = 1) or variable (γ < 1) range hopping (VRH) models.
<display-eqn id="jphysd321180eq006" eqnnum="6"></display-eqn>
The constants <italic>A</italic> and <italic>T</italic><sub>0</sub> depend on the localization and density of the states; the exponents <italic>b</italic> and γ depend on the distribution of states around the Fermi level; the value of γ in particular, is related to the dimension of the transport process, <italic>d</italic>, as follows:
<display-eqn id="jphysd321180eq007" eqnnum="7"></display-eqn>
In three dimensions, when the density of the localized states near the Fermi level does not depend on energy, γ is equal to 1/4. The bi-dimensional VRH is obtained for <italic>d</italic> = 2 (γ = 1/3) and the one-dimensional VRH is found for <italic>d</italic> = 1 (γ = 1/2).</p><p>The FIT model was proposed for a granular system in which large regions of a highly conductive (‘metallic’) phase in an inhomogeneous material are separated from each other by an insulating phase acting as a potential barrier [<cite linkend="jphysd321180bib16">16</cite>, <cite linkend="jphysd321180bib17">17</cite>]. In the FIT model the conductivity is given by
<display-eqn id="jphysd321180eq008" eqnnum="8"></display-eqn>
where σ<sub>0</sub> is a constant, <italic>T</italic><sub>0</sub> is the temperature below which the tunnelling effect is independent of temperature and <italic>T</italic><sub>1</sub> is the temperature below which the conductivity is thermally activated (<italic>T</italic><sub>1</sub> depends on the average potential barrier height).</p><p>The variation of dc conductivity, σ<sub>dc</sub>, with temperature is shown in figure <figref linkend="jphysd321180fig04">4(<italic>a</italic>)</figref> for the PANI/DCAA films and in figure <figref linkend="jphysd321180fig04">4(<italic>b</italic>)</figref> for the PANI/DCAA–FA films. We observe an increase in σ<sub>dc</sub> with temperature. This indicates a semiconductor behaviour [<cite linkend="jphysd321180bib18">18</cite>] for both PANI/DCAA and PANI/DCAA–FA. For the same temperature, the PANI/DCAA films are shown to be more conductive than the PANI/DCAA–FA ones. The obtained values of conductivity for both series of PANI films are coherent with those found generally for conducting polymer films [<cite linkend="jphysd321180bib19">19</cite>].
<figure id="jphysd321180fig04" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/jphysd321180fig04.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/jphysd321180fig04.jpg"></graphic-file></graphic><caption id="jphysd321180fc04" label="Figure 4"><p indent="no">Variation of the dc conductivity of (<italic>a</italic>) PANI/DCAA films and (<italic>b</italic>) PANI/DCAA–FA films with temperature.</p></caption></figure></p><p>We have undertaken a fitting procedure of the conductivity data of PANI films using the previously cited conduction models. The best fits were obtained with the 3D VRH conduction model for the PANI/DCAA films and the FIT model for the PANI/DCAA–FA films.</p><p>In the 3D VRH model, when the interactions between charge carriers are neglected, the thermal dependence of dc conductivity is expressed as follows [<cite linkend="jphysd321180bib09">9</cite>]:
<display-eqn id="jphysd321180eq009" eqnnum="9"></display-eqn>
where <italic>B</italic> is a constant depending on the distribution of localized states around the Fermi level and <italic>T</italic><sub>0</sub> is the Mott characteristic temperature. It corresponds to the hopping barrier for charge carriers and measures the degree of disorder in the studied system. It is given by [<cite linkend="jphysd321180bib09">9</cite>]
<display-eqn id="jphysd321180eq010" eqnnum="10"></display-eqn>
where <italic>N</italic>(<italic>E</italic><sub>F</sub>) is the density of states at the Fermi level, <italic>k</italic><sub>B</sub> is the Boltzmann constant and 1/α is the decay length of the localized wavefunction.</p><p>The average hopping distance <italic>R</italic><sub>hop</sub> and the average hopping energy <italic>W</italic><sub>hop</sub> are given, respectively, by [<cite linkend="jphysd321180bib09">9</cite>]
<display-eqn id="jphysd321180eq011" eqnnum="11"></display-eqn><display-eqn id="jphysd321180eq012" eqnnum="12"></display-eqn>
In figure <figref linkend="jphysd321180fig05">5</figref>, we have plotted log (σ<sub>dc</sub>. <italic>T</italic><sup>1/2</sup>) versus <italic>T</italic><sup>−1/4</sup> for the three cast PANI/DCAA films. The linear behaviour of the plots indicates that the 3D VRH mechanism dominates in the [90, 300 K] temperature range. The slopes of the straight lines give the value of <italic>T</italic><sub>0</sub> for each sample. Various Mott parameters calculated from equations (<eqnref linkend="jphysd321180eq009">9</eqnref>), (<eqnref linkend="jphysd321180eq010">10</eqnref>), (<eqnref linkend="jphysd321180eq011">11</eqnref>) and (<eqnref linkend="jphysd321180eq012">12</eqnref>), assuming α<sup>−1</sup> to be 1.1 nm [<cite linkend="jphysd321180bib18">18</cite>] and evaluated at 250 K, are listed in table <tabref linkend="jphysd321180tab01">1</tabref>. It is clear from this table that <italic>T</italic><sub>0</sub> increases when the dc conductivity decreases. We also note that when the density of the localized states <italic>N</italic>(<italic>E</italic><sub>F</sub>) increases, the film conductivity becomes higher. On the other hand, the increase in the conductivity parallels the decrease in the average hopping distance <italic>R</italic><sub>hop</sub> and the average hopping energy <italic>W</italic><sub>hop</sub>. Those results are consistent with Mott's requirements, <italic>R</italic><sub>hop</sub> α > 1 and <italic>W</italic><sub>hop</sub> > <italic>k</italic><sub>B</sub><italic>T</italic>. <italic>R</italic><sub>hop</sub> α called the degree of localization [<cite linkend="jphysd321180bib18">18</cite>], is found to be 2.15 for PANI/DCAA cast at 353 K and 2.05 for PANI/DCAA cast at 298 K at <italic>T</italic> = 250 K. This indicates that the charge carriers become more localized and explains the associated decrease observed in the conductivity.
<figure id="jphysd321180fig05" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/jphysd321180fig05.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/jphysd321180fig05.jpg"></graphic-file></graphic><caption id="jphysd321180fc05" label="Figure 5"><p indent="no">VRH 3D model for the PANI/DCAA films.</p></caption></figure><table id="jphysd321180tab01" type="formal" frame="topbot" colsep="no" rowsep="no"><caption id="jphysd321180tc01" label="Table 1"><p indent="no">Parameters of the VRH 3D model.</p></caption><tgroup cols="7" colsep="no" rowsep="no" align="center" charoff="50" char=""><colspec colnum="1" colname="1" align="left" colwidth="1*"></colspec><colspec colnum="2" colname="2" align="right" colwidth="1*"></colspec><colspec colnum="3" colname="3" align="left" colwidth="1*"></colspec><colspec colnum="4" colname="4" align="left" colwidth="1*"></colspec><colspec colnum="5" colname="5" align="left" colwidth="1*"></colspec><colspec colnum="6" colname="6" align="left" colwidth="1*"></colspec><colspec colnum="7" colname="7" align="left" colwidth="1*"></colspec><thead><row rowsep="yes"><entry>Samples</entry><entry>σ<sub>dc</sub> (S m<sup>−1</sup>) (<italic>T</italic> = 250 K)</entry><entry><italic>T</italic><sub>0</sub>(K)</entry><entry><italic>N</italic>(<italic>E</italic><sub>F</sub>) (eV<sup>−1</sup> nm<sup>−3</sup>) (<italic>T</italic> = 250 K)</entry><entry><italic>R</italic><sub>hop</sub> (nm) (<italic>T</italic> = 250 K)</entry><entry><italic>W</italic><sub>hop</sub> (meV) (<italic>T</italic> = 250 K)</entry><entry>α<italic>R</italic><sub>hop</sub> (<italic>T</italic> = 250 K)</entry></row></thead><tbody><row><entry>PANI/DCAA (298 K)</entry><entry>2160</entry><entry>2.25 × 10<sup>5</sup></entry><entry>0.70</entry><entry>2.26</entry><entry>29.5</entry><entry>2.05</entry></row><row><entry>PANI/DCAA (353 K)</entry><entry>889</entry><entry>2.71 × 10<sup>5</sup></entry><entry>0.58</entry><entry>2.37</entry><entry>30.9</entry><entry>2.15</entry></row><row><entry>PANI/DCAA (318 K)</entry><entry>389</entry><entry>4.08 × 10<sup>5</sup></entry><entry>0.39</entry><entry>2.62</entry><entry>34.2</entry><entry>2.38</entry></row></tbody></tgroup></table></p><p>For the PANI/DCAA–FA films, the conduction mechanism follows a FIT model [<cite linkend="jphysd321180bib17">17</cite>] expressed by equation (<eqnref linkend="jphysd321180eq008">8</eqnref>) in the temperature range [90, 300 K] (see figure <figref linkend="jphysd321180fig06">6</figref>). The various FIT parameters were calculated and are summarized in table <tabref linkend="jphysd321180tab02">2</tabref>.
<figure id="jphysd321180fig06" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/jphysd321180fig06.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/jphysd321180fig06.jpg"></graphic-file></graphic><caption id="jphysd321180fc06" label="Figure 6"><p indent="no">FIT model for the PANI/DCAA–FA films.</p></caption></figure><table id="jphysd321180tab02" type="formal" frame="topbot" colsep="no" rowsep="no"><caption id="jphysd321180tc02" label="Table 2"><p indent="no">Parameters of the FIT model.</p></caption><tgroup cols="6" colsep="no" rowsep="no" align="center" charoff="50" char=""><colspec colnum="1" colname="1" align="left" colwidth="1*"></colspec><colspec colnum="2" colname="2" align="char" char="." colwidth="1*"></colspec><colspec colnum="3" colname="3" align="right" colwidth="1*"></colspec><colspec colnum="4" colname="4" align="left" colwidth="1*"></colspec><colspec colnum="5" colname="5" align="left" colwidth="1*"></colspec><colspec colnum="6" colname="6" align="char" char="." colwidth="1*"></colspec><thead><row rowsep="yes"><entry>Samples</entry><entry>σ<sub>dc</sub> (S m<sup>−1</sup>) (<italic>T</italic> = 250 K)</entry><entry><italic>T</italic><sub>1</sub> (K)</entry><entry><italic>k</italic><sub>B</sub> <italic>T</italic><sub>1</sub> (eV)</entry><entry>σ<sub>0</sub></entry><entry><italic>T</italic><sub>0</sub> (K)</entry></row></thead><tbody><row><entry>PANI/DCAA–FA (353 K)</entry><entry>21.4</entry><entry>3 675</entry><entry>0.31</entry><entry>1.03 × 10<sup>5</sup></entry><entry>346.7</entry></row><row><entry>PANI/DCAA–FA (298 K)</entry><entry>6.3</entry><entry>9 107</entry><entry>1.25</entry><entry>6.58 × 10<sup>5</sup></entry><entry>537.8</entry></row><row><entry>PANI/DCAA–FA (318 K)</entry><entry>3.3</entry><entry>16 903</entry><entry>1.46</entry><entry>5.18 × 10<sup>12</sup></entry><entry>1332.9</entry></row></tbody></tgroup></table></p></sec-level2><sec-level2 id="jphysd321180s3-4" label="3.4"><heading>Discussion</heading><sec-level3 id="jphysd321180s3-4-1" label="3.4.1"><heading>Casting temperature effect</heading><p indent="no">It is clear from the data shown in figures <figref linkend="jphysd321180fig01">1</figref> and <figref linkend="jphysd321180fig04">4</figref> that either PANI/DCAA or PANI/DCAA–FA films cast at 318 K (around the transition temperature) have the lowest conductivity and crystallinity. So, it is advisable to avoid the dispersion phase transition temperature domains in order to get conducting PANI films with the highest conductivities. In fact, the transition introduces a structural disorder that opposes the extension of crystalline regions in the cast films.</p><p>Discontinuities in FTIR measurements and resistivity measurements were reported in the literature [<cite linkend="jphysd321180bib20">20</cite>] for doped and undoped PANI films. They were attributed to the presence of a conformational transition at 353 K, an analogue of a glass transition [<cite linkend="jphysd321180bib21">21</cite>].</p><p>An interesting relation can also be observed between the conducting properties and the structural properties. In fact, the more crystalline films are the more conductive. If we build a classification by decreasing crystallinity, we find that for the PANI/DCAA films, the one cast at 298 K is more crystalline than that at 353 K, which is more crystalline than that at 318 K. For PANI/DCAA–FA, the one cast at 353 K is more crystalline than that at 298 K, which is more crystalline than that at 318 K. The same classification is found for the conductivity, thus indicating at least a qualitative relation between these two physical parameters. Such a correlation is quite logical as it is well known that the crystalline parts are more conductive than the amorphous ones [<cite linkend="jphysd321180bib19">19</cite>, <cite linkend="jphysd321180bib22" range="bib22,bib23,bib24">22–24</cite>].</p></sec-level3><sec-level3 id="jphysd321180s3-4-2" label="3.4.2"><heading>Solvent type effect</heading><p indent="no">When considering the solvent type, we observe that by the replacement of 20% in volume of FA instead of DCAA (PANI/DCAA<sub>0.8</sub>–FA<sub>0.2</sub>), there is a slump in the value of the dc conductivities by two orders of magnitude. This solvent effect can be associated with the differences in the interactions between PANI and each solvent. Different interactions lead to different final morphologies influencing the crystallinity and the conductivity [<cite linkend="jphysd321180bib19">19</cite>]. Besides, the conduction mechanism was also dependent on the solvent type. A 3D VRH model was found for the PANI/DCAA films (more crystalline) and a FIT model was found for the PANI/DCAA–FA films (more amorphous). The found conduction models are coherent with the expected conduction mechanisms. In fact, the conductivity of the crystalline parts is dominant in PANI/DCAA and the conductivity of the amorphous parts is dominant in PANI/DCAA–FA. Hence, it is interesting to look for the experimental conditions leading to the highest crystallinity (298 K for PANI/DCAA).</p></sec-level3></sec-level2></sec-level1><sec-level1 id="jphysd321180s4" label="4"><heading>Conclusion</heading><p indent="no">The purpose of this study is to cast PANI films with the highest conductivity. The effect of the solvent type and the casting temperature on the electrical properties of plastdoped PANI films were investigated using conductivity studies and the x-ray diffraction technique. We found that the conduction mechanism was dependent on the solvent type. A 3D VRH model was found for the PANI/DCAA films and a FIT model was found for the PANI/DCAA–FA films. We also observed that the replacement of 20% in volume of DCAA by FA induced a drop in the value of dc conductivities by two orders of magnitude.</p><p>Besides, through this study we were able to prove that the casting temperature at which the PANI films are formed is also important. For PANI/DCAA, we observed a conductivity which was one order of magnitude higher between films formed at 298 and 318 K. The films cast at temperatures around the second order liquid–liquid structural transition temperature of PANI dispersions lead to the lowest conductivity, regardless of the solvent type used.</p><p>A qualitative correlation was also found between the conductivity and the crystallinity of the PANI films. Hence, in order to obtain films with the highest electric conductivities, we must apply experimental conditions leading to the highest crystallinity (298 K for PANI/DCAA).</p></sec-level1></body><back><references><heading>References</heading><reference-list type="numeric"><journal-ref id="jphysd321180bib01" num="1"><authors><au><second-name>Gosh</second-name><first-names>A M</first-names></au><au><second-name>Barman</second-name><first-names>A K</first-names></au><au><second-name>Meikap</second-name><first-names>S K</first-names></au><au><second-name>Chatterjee De</second-name><first-names>S</first-names></au></authors><year>1999</year><jnl-title>Phys. 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PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAAFA)). Previous work showed that at around 318K, a second order liquidliquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 room temperature, 318 and 353K). The electrical properties of the cast films were investigated in the frequency range 100Hz1MHz. The temperature was varied between 20 and 300K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAAFA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.</abstract><subject><genre>keywords</genre><topic>Conductivity mechanism</topic><topic>conducting polymer</topic><topic>processing parameters</topic><topic>structure</topic></subject><classification authority="pacs">72.80.r</classification><relatedItem type="host"><titleInfo><title>Journal of Physics D: Applied Physics</title></titleInfo><titleInfo type="abbreviated"><title>J. Phys. D: Appl. Phys.</title></titleInfo><genre type="journal">journal</genre><identifier type="ISSN">0022-3727</identifier><identifier type="eISSN">1361-6463</identifier><identifier type="PublisherID">jphysd</identifier><identifier type="CODEN">JPAPBE</identifier><identifier type="URL">stacks.iop.org/JPhysD</identifier><part><date>2009</date><detail type="volume"><caption>vol.</caption><number>42</number></detail><detail type="issue"><caption>no.</caption><number>20</number></detail><extent unit="pages"><start>1</start><end>7</end><total>7</total></extent></part></relatedItem><identifier type="istex">5321363D38B206309A5FCB2F8D22724D94B58756</identifier><identifier type="DOI">10.1088/0022-3727/42/20/205404</identifier><identifier type="PII">S0022-3727(09)21180-6</identifier><identifier type="articleID">321180</identifier><identifier type="articleNumber">205404</identifier><accessCondition type="use and reproduction" contentType="copyright">2009 IOP Publishing Ltd</accessCondition><recordInfo><recordContentSource>IOP</recordContentSource><recordOrigin>2009 IOP Publishing Ltd</recordOrigin></recordInfo></mods></metadata><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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