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XPS approach to structural change in conducting PPy
ELSEVIER
Synthetic Metals 101 (1999) 19
An XEWXPS
approach to structural change in conducting PPy
K. Cheah“, M. Forsytha,V.-T. Truongb aDepartmentofMaterials Engineeting,MonashUniversity, WellingtonRoad,Clayton3168,Vie.,Australia bDSTO,AeronauticalandMatitime ResearchLabomtoly, Maritime PlalfonnsDivision,PO Box 4331,Melbourne3001,Kc., Australia Abstract Electrochemicallysynthesised polypyrrole (PPy) with 1,5naphthalenedisulfonate(I,5-NDS) counterionstreatedwith simpleacid and basewascharacterised usingX-ray diffraction (XRD) andX-ray photoelectronspectroscopy (XPS). The assynthesised film wasfound to be amorphouswith short-rangeorderingin the polymer backbone.Orderingwaslost after thermalageingwith evidenceof counterion degradation.Basetreatmentlead to lossof orderingas well as dedopingof the polymer whereasacid treatmentat high temperature increasesshortrangeordering.Conductivity wasalsoincreaseddramaticallywith evidenceof ion exchange.Orderinginducedby the treatmentwasmaintainedevenafter thermalageing. Keywords:Ordering;X-ray diffraction; Ion exchange;Conductivity; Thermalageing Treatment
%A(N+/N) %A(S/N) %Ao/ot (after ageing) 60 n-insH2S04at 100°C -36 12.7 9.6 -19.4 19.0 16.7 60 minsHiSO4at RT -33 i 2.5 60 minsNaOH at RT -24 5 1.8 -37.2 -76.9 Untreated -42 k 3.2 Table 1. Conductivity,andchemicalcomposition(asdeterminedby XPS) changeof assynthesised PPy after acid andbasetreatmentand thermalageingat 150°Cfor 60 days(whereAo = or-o,,,o0is the initial conductivity andAN/N) = [w/N), - o\r’/N),]! o\T’/N),) %A&, (after treatment) 91 +6.8 12i 0.9 -38 * 2.8
The enhancedstability of electrochemicallysynthesisedPPy films can be achievedby treatmentwith simpleacid and base. The mechanismfor the enhancedstability is not understood althoughthe decrease in permeabilityof the films to oxygen and water hasbeenreportedto occur. The degreeof stabilisationwas found to be dependentonthe solution,temperatureandtreatment time. The aim of this work is to investigatethe relationship betweenconductivity, microstructureand stability of conducting PPy from acidandbasetreatment. PPy/l,S-NDS fllrns were synthesisedgalvanostaticallyand treated with 1MH2S04 or O.lM NaOH treatment at room temperature. High temperatureacid treatmentwas conductedby refluxing the ftis in boiling acid Treatedfilms wereagedin dry air at 150°Cfor 60 days.Resultsin Table 1. XRD wasperformed on fresh and agedsampleusinga diffractomerequippedwith a solidstategermaniumdetector.XPS analysiswasalsoconducted. Treatment of PPy/l,S-NDS with acid at high temperature resultsin significantincreasein conductivity dueto ion exchange with so‘jz- anion as shown with the reduction in S/N ratio. Thermal stability is poor but overall residual conductivity is highest among all samples.Treatment with acid at room temperatureresultsin marginal increasein conductivity as a result of protonationbut only slight improvementin stability compared to the untreated sample. Base treatment lowers conductivity but confersthe best conductivity stability. Lossof conductivity can be attributedto ion exchangebetweenthe 1,5NDS andthe OH ionsaswell asthe deprotonationasshownwith lowernitrogenspecieswith delocalisedchargecr\r’)anddedoping of the polymer. XRD showsthat the as-synthesised film is amorphouswith a broadpeak that can be resolvedinto two peaksat 20” and 26” (Fig. 1). The highangle peakarisesfrom the interplanarvan der Waals spacingbetweenpyrrole groupsand the low anglepeak from pyrrole-counterionor inter-counterioninteractionscattering. Thermalageingresultsin the reductionin intensityof the broad
peakindicatingthe lossof pyrrole structureandcounterion.Base treatment producessimilar reduction in the intensity of the scatteringpeak (Fig. 1). Acid treatment at high temperature showsremarkableimprovementin PPy chainorderingaspeaksat 20” and 26’ arebetter resolved.A new inter-counterionpeakat 15.5” was observedas a result of ion exchangeduring acid treatment.Ordering wasmaintainedafter thermalageingand is reflected in the high residualconductivity. Room temperature acid treatmentresultsin similarimprovementin chain ordering and a new low anglepeakat 10.5” attributedto the orderingof the incorporatedanionas a result of protonation.However, the inducedorderingwaslost after thermalageing. Basedon the XRD andconductivity resultsthe increaseshort rangeorderingin thepolymer film increases conductivity but not conductivity stability, which may be governedby other chemical changes.
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Fig. 1. XRD spectraof PPy/l,S-NDS; i) as-synthesised, ii) base treated,andiii) treatedwith 1M H2S04for 60 minat 100°C. References 1. K. Cheah,M. Forsyth, V.- T. Truong,Synth.Met. 94 (1998) 2 15-219andreferencestherein
0379-6779/99/$ - see front matter 0 1999 Elsevier Science .%A. All rights reserved. PII: SO379-6779(98)00790-5
Synthetic Metals 101 (1999) 19
An XEWXPS
approach to structural change in conducting PPy
K. Cheah“, M. Forsytha,V.-T. Truongb aDepartmentofMaterials Engineeting,MonashUniversity, WellingtonRoad,Clayton3168,Vie.,Australia bDSTO,AeronauticalandMatitime ResearchLabomtoly, Maritime PlalfonnsDivision,PO Box 4331,Melbourne3001,Kc., Australia Abstract Electrochemicallysynthesised polypyrrole (PPy) with 1,5naphthalenedisulfonate(I,5-NDS) counterionstreatedwith simpleacid and basewascharacterised usingX-ray diffraction (XRD) andX-ray photoelectronspectroscopy (XPS). The assynthesised film wasfound to be amorphouswith short-rangeorderingin the polymer backbone.Orderingwaslost after thermalageingwith evidenceof counterion degradation.Basetreatmentlead to lossof orderingas well as dedopingof the polymer whereasacid treatmentat high temperature increasesshortrangeordering.Conductivity wasalsoincreaseddramaticallywith evidenceof ion exchange.Orderinginducedby the treatmentwasmaintainedevenafter thermalageing. Keywords:Ordering;X-ray diffraction; Ion exchange;Conductivity; Thermalageing Treatment
%A(N+/N) %A(S/N) %Ao/ot (after ageing) 60 n-insH2S04at 100°C -36 12.7 9.6 -19.4 19.0 16.7 60 minsHiSO4at RT -33 i 2.5 60 minsNaOH at RT -24 5 1.8 -37.2 -76.9 Untreated -42 k 3.2 Table 1. Conductivity,andchemicalcomposition(asdeterminedby XPS) changeof assynthesised PPy after acid andbasetreatmentand thermalageingat 150°Cfor 60 days(whereAo = or-o,,,o0is the initial conductivity andAN/N) = [w/N), - o\r’/N),]! o\T’/N),) %A&, (after treatment) 91 +6.8 12i 0.9 -38 * 2.8
The enhancedstability of electrochemicallysynthesisedPPy films can be achievedby treatmentwith simpleacid and base. The mechanismfor the enhancedstability is not understood althoughthe decrease in permeabilityof the films to oxygen and water hasbeenreportedto occur. The degreeof stabilisationwas found to be dependentonthe solution,temperatureandtreatment time. The aim of this work is to investigatethe relationship betweenconductivity, microstructureand stability of conducting PPy from acidandbasetreatment. PPy/l,S-NDS fllrns were synthesisedgalvanostaticallyand treated with 1MH2S04 or O.lM NaOH treatment at room temperature. High temperatureacid treatmentwas conductedby refluxing the ftis in boiling acid Treatedfilms wereagedin dry air at 150°Cfor 60 days.Resultsin Table 1. XRD wasperformed on fresh and agedsampleusinga diffractomerequippedwith a solidstategermaniumdetector.XPS analysiswasalsoconducted. Treatment of PPy/l,S-NDS with acid at high temperature resultsin significantincreasein conductivity dueto ion exchange with so‘jz- anion as shown with the reduction in S/N ratio. Thermal stability is poor but overall residual conductivity is highest among all samples.Treatment with acid at room temperatureresultsin marginal increasein conductivity as a result of protonationbut only slight improvementin stability compared to the untreated sample. Base treatment lowers conductivity but confersthe best conductivity stability. Lossof conductivity can be attributedto ion exchangebetweenthe 1,5NDS andthe OH ionsaswell asthe deprotonationasshownwith lowernitrogenspecieswith delocalisedchargecr\r’)anddedoping of the polymer. XRD showsthat the as-synthesised film is amorphouswith a broadpeak that can be resolvedinto two peaksat 20” and 26” (Fig. 1). The highangle peakarisesfrom the interplanarvan der Waals spacingbetweenpyrrole groupsand the low anglepeak from pyrrole-counterionor inter-counterioninteractionscattering. Thermalageingresultsin the reductionin intensityof the broad
peakindicatingthe lossof pyrrole structureandcounterion.Base treatment producessimilar reduction in the intensity of the scatteringpeak (Fig. 1). Acid treatment at high temperature showsremarkableimprovementin PPy chainorderingaspeaksat 20” and 26’ arebetter resolved.A new inter-counterionpeakat 15.5” was observedas a result of ion exchangeduring acid treatment.Ordering wasmaintainedafter thermalageingand is reflected in the high residualconductivity. Room temperature acid treatmentresultsin similarimprovementin chain ordering and a new low anglepeakat 10.5” attributedto the orderingof the incorporatedanionas a result of protonation.However, the inducedorderingwaslost after thermalageing. Basedon the XRD andconductivity resultsthe increaseshort rangeorderingin thepolymer film increases conductivity but not conductivity stability, which may be governedby other chemical changes.
0
10
20 28
30
40
Fig. 1. XRD spectraof PPy/l,S-NDS; i) as-synthesised, ii) base treated,andiii) treatedwith 1M H2S04for 60 minat 100°C. References 1. K. Cheah,M. Forsyth, V.- T. Truong,Synth.Met. 94 (1998) 2 15-219andreferencestherein
0379-6779/99/$ - see front matter 0 1999 Elsevier Science .%A. All rights reserved. PII: SO379-6779(98)00790-5