Nigel A. Surridge, J. C. Jernigan, E. F. Dalton, R. Buck, M. Watanabe, H. Zhang, M. Pinkerton, T. T. Wooster, M. Longmire, J. S. Facci, R. Murray
Using microelectrochemical techniques, our laboratory has explored self-exchange-based electron transport in a variety of mixed-valent polymeric media. The transport rate is measured as the electron diffusion coefficient, De, or the self-exchange rate constant kex. The basic variables for electron transport in mixed-valent polymer materials include: (a) the physical mobility of the counterions of the polymer that migrate due to electroneutrality requirements, (b) the physical diffusion coefficient, Dphys, of the monomeric or polymeric oxidized and reduced molecular sites or ions relative to the rate of electron hopping or tunnelling between donor/acceptor pairs, (c) the observational timescale relative to these mobilities which provides the distinction between transient and steady-state experiments, and (d) the chemical environment of the polymer, whether dry and solvent-free or contacted by solvent vapour or liquid. Experimental strategies and results are presented for the measurement of rates of ion diffusion, Di, in N2-dry and solvent-wetted mixed valent polymers. In a dry, mixed-valent osmium complex polymer, the electron-transport rate measured under steady-state conditions, where no ion transport occurs concurrently, is much faster than the diffusion rate of the ion as estimated in a transient electrolysis experiment. In a solvent-wetted osmium complex polymer, the electron-transport rate measured under transient conditions is much slower than that of the ion which was measured under steady-state conditions. These circumstances allow isolation of individual processes and are interpreted as giving electron-transport rates not strongly influenced by macroscopic ion-transport rates. Cyclic voltammetry of [Co(bpy)3]2+ and of Li+TCNQ– in dry poly(ethylene oxide) polymer electrolyte solvents exhibits differing measured diffusion coefficients, Dapp, for the oxidation vs. the reduction of each compound, reflecting the coupling of physical diffusion and electron self-exchange transport. Microdisc electrode voltammetry of solutions of a synthesized ferrocene mono-tagged poly(ethylene oxide) in a polymer solvent of comparable molecular weight gives Dapp values smaller than those for ferrocene monomer dissolved in the same polymer solvent. The Dapp in the former case measures the self-diffusion rate of a linear chain polymer within a linear chain polymer solvent. Measurability of this rate has implications for assumptions about diffusive mobility of redox molecules attached to polymer chains.
{"title":"The Electrochemistry Group Medal Lecture. Electron self-exchange dynamics between redox sites in polymers","authors":"Nigel A. Surridge, J. C. Jernigan, E. F. Dalton, R. Buck, M. Watanabe, H. Zhang, M. Pinkerton, T. T. Wooster, M. Longmire, J. S. Facci, R. Murray","doi":"10.1039/DC9898800001","DOIUrl":"https://doi.org/10.1039/DC9898800001","url":null,"abstract":"Using microelectrochemical techniques, our laboratory has explored self-exchange-based electron transport in a variety of mixed-valent polymeric media. The transport rate is measured as the electron diffusion coefficient, De, or the self-exchange rate constant kex. The basic variables for electron transport in mixed-valent polymer materials include: (a) the physical mobility of the counterions of the polymer that migrate due to electroneutrality requirements, (b) the physical diffusion coefficient, Dphys, of the monomeric or polymeric oxidized and reduced molecular sites or ions relative to the rate of electron hopping or tunnelling between donor/acceptor pairs, (c) the observational timescale relative to these mobilities which provides the distinction between transient and steady-state experiments, and (d) the chemical environment of the polymer, whether dry and solvent-free or contacted by solvent vapour or liquid. Experimental strategies and results are presented for the measurement of rates of ion diffusion, Di, in N2-dry and solvent-wetted mixed valent polymers. In a dry, mixed-valent osmium complex polymer, the electron-transport rate measured under steady-state conditions, where no ion transport occurs concurrently, is much faster than the diffusion rate of the ion as estimated in a transient electrolysis experiment. In a solvent-wetted osmium complex polymer, the electron-transport rate measured under transient conditions is much slower than that of the ion which was measured under steady-state conditions. These circumstances allow isolation of individual processes and are interpreted as giving electron-transport rates not strongly influenced by macroscopic ion-transport rates. Cyclic voltammetry of [Co(bpy)3]2+ and of Li+TCNQ– in dry poly(ethylene oxide) polymer electrolyte solvents exhibits differing measured diffusion coefficients, Dapp, for the oxidation vs. the reduction of each compound, reflecting the coupling of physical diffusion and electron self-exchange transport. Microdisc electrode voltammetry of solutions of a synthesized ferrocene mono-tagged poly(ethylene oxide) in a polymer solvent of comparable molecular weight gives Dapp values smaller than those for ferrocene monomer dissolved in the same polymer solvent. The Dapp in the former case measures the self-diffusion rate of a linear chain polymer within a linear chain polymer solvent. Measurability of this rate has implications for assumptions about diffusive mobility of redox molecules attached to polymer chains.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"96 1","pages":"1-17"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80820680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Under appropriate conditions, single-crystal observations are capable of yielding information about reaction mechanisms and transport phenomena which can assist in understanding the behaviour of practical, high metal area, supported catalysts. In the case of chemical catalysis by metals, the literature contains a number of well documented examples of which illustrate the success of this approach. Corresponding model studies of the metal/oxide interface are less common, although in principle they should be capable of improving our understanding of those systems in which metal/support interactions play an important role in determining the catalytic chemistry. This paper deals with the application of such methods to two areas of synthesis gas chemistry; additionally, correlated measurements have been made on the structure and reactivity of the corresponding high-area catalysts. The usefulness of such a combined approach will be illustrated with reference to methanol synthesis over copper/rare-earth oxide systems and the behaviour of Ru/TiO catalysts.
{"title":"Chemistry and catalysis at the metal/metal oxide interface","authors":"J. Badyal, R. M. Nix, T. Rayment, R. M. Lambert","doi":"10.1039/DC9898700121","DOIUrl":"https://doi.org/10.1039/DC9898700121","url":null,"abstract":"Under appropriate conditions, single-crystal observations are capable of yielding information about reaction mechanisms and transport phenomena which can assist in understanding the behaviour of practical, high metal area, supported catalysts. In the case of chemical catalysis by metals, the literature contains a number of well documented examples of which illustrate the success of this approach. Corresponding model studies of the metal/oxide interface are less common, although in principle they should be capable of improving our understanding of those systems in which metal/support interactions play an important role in determining the catalytic chemistry. This paper deals with the application of such methods to two areas of synthesis gas chemistry; additionally, correlated measurements have been made on the structure and reactivity of the corresponding high-area catalysts. The usefulness of such a combined approach will be illustrated with reference to methanol synthesis over copper/rare-earth oxide systems and the behaviour of Ru/TiO catalysts.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"30 1","pages":"121-132"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74944193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Transition-metal oxides supported on and chemically interacting with the surface of SiO2, Al2O3, TiO2etc. form discrete monolayers of species unlike those found at the surface of the unsupported oxides, being in effect two-dimensional compounds. Areas of their application include alkene metathesis and polymerisation, selective reduction of NO by NH3, and selective oxidation of aromatics. They are readily detected by Raman spectroscopy, FTIR and EXAFS/XANES, and thermal methods and XPS assist their characterisation. They can exhibit strong acidic character, mainly of the Bronsted type; whereas isopropyl alcohol decomposition on MoO3TiO2 gives chiefly dehydration, the main product over V2O5/TiO2 is acetone. The unique ability of the latter system to catalyse the selective oxidation of o-xylene to phthalic anhydride is attributed to the ability of the surface species to undergo oxidative addition at VO groups and to effect the elimination of H atoms in adsorbed radicals as water. When the amount of supported oxide exceeds the monolayer capacity, two further forms of the oxide are detectable, both differing in their reactivity from that of the bulk oxide.
{"title":"Structure and reactivity of transition-metal oxide monolayers","authors":"G. Bond, S. Flamerz, R. Shukri","doi":"10.1039/DC9898700065","DOIUrl":"https://doi.org/10.1039/DC9898700065","url":null,"abstract":"Transition-metal oxides supported on and chemically interacting with the surface of SiO2, Al2O3, TiO2etc. form discrete monolayers of species unlike those found at the surface of the unsupported oxides, being in effect two-dimensional compounds. Areas of their application include alkene metathesis and polymerisation, selective reduction of NO by NH3, and selective oxidation of aromatics. They are readily detected by Raman spectroscopy, FTIR and EXAFS/XANES, and thermal methods and XPS assist their characterisation. They can exhibit strong acidic character, mainly of the Bronsted type; whereas isopropyl alcohol decomposition on MoO3TiO2 gives chiefly dehydration, the main product over V2O5/TiO2 is acetone. The unique ability of the latter system to catalyse the selective oxidation of o-xylene to phthalic anhydride is attributed to the ability of the surface species to undergo oxidative addition at VO groups and to effect the elimination of H atoms in adsorbed radicals as water. When the amount of supported oxide exceeds the monolayer capacity, two further forms of the oxide are detectable, both differing in their reactivity from that of the bulk oxide.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"46 1","pages":"65-77"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76489663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The anchoring process of Cr(Cp)2 on silica hydroxyl groups occurs by elimination of C5H6 and formation of Si—O—CrCp mononuclear species. These anchored species are then able to adsorb incoming Cr(Cp)2 to give catalytically inactive dimeric species. These reactions are heavily diffusion-controlled. Interaction of CO and NO with mononuclear anchored species gives well defined dicarbonylic and dinitrosylic compounds, while the reaction of CO with dinuclear (catalytically inactive) species gives much more complex polycarbonylic compounds. The Si—O—CrCp mononuclear surface species are the active sites for ethene polymerization. The chain-initiation mechanism probably consists of the formation of a metallocyclic structure.
{"title":"Interaction of chromocene with the silica surface, and structure of the active species for ethene polymerization","authors":"A. Zecchina, G. Spoto, S. Bordiga","doi":"10.1039/DC9898700149","DOIUrl":"https://doi.org/10.1039/DC9898700149","url":null,"abstract":"The anchoring process of Cr(Cp)2 on silica hydroxyl groups occurs by elimination of C5H6 and formation of Si—O—CrCp mononuclear species. These anchored species are then able to adsorb incoming Cr(Cp)2 to give catalytically inactive dimeric species. These reactions are heavily diffusion-controlled. Interaction of CO and NO with mononuclear anchored species gives well defined dicarbonylic and dinitrosylic compounds, while the reaction of CO with dinuclear (catalytically inactive) species gives much more complex polycarbonylic compounds. The Si—O—CrCp mononuclear surface species are the active sites for ethene polymerization. The chain-initiation mechanism probably consists of the formation of a metallocyclic structure.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"44 1","pages":"149-160"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82356738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Lunsford, M. Cisneros, P. Hinson, Youdong Tong, Hong-sheng Zhang
Pure MgO samples having greatly different morphologies and lithium-promoted catalysts derived from these materials have been examined by electron microscopy. In addition, their ability to generate and react with gas-phase methyl radicals has been determined using e.s.r. in combination with a matrix-isolation technique. Lithium caused the MgO to sinter severely at 700 °C, but the resulting material showed improved activity for the generation of methyl radicals. These factors gave rise to catalysts which were moderately active and selective for the oxidative dimerization of CH4 at 700 °C (up to 20% conversion, 66% C2+ selectivity). The results are particularly significant in that catalysts which had been prepared such that the lithium was initially present as Li2O on the surface exhibited almost constant C2+ production as the Li2O was converted to Li2CO3. Thus, neither Li2O nor Li2CO3 is the active phase for the selective conversion of CH4. A catalyst prepared from Li2CO3 and MgO sintered much less extensively, produced more CH3˙ radicals and gave higher yields of C2+ hydrocarbons. A comparison of these catalytic properties suggests that surface area and related morphological factors do not have an adverse effect on the oxidative dimerization reaction, provided the surface can be rendered inert to secondary reactions with methyl radicals.
{"title":"Oxidative dimerization of methane over well defined lithium-promoted magnesium oxide catalysts","authors":"J. Lunsford, M. Cisneros, P. Hinson, Youdong Tong, Hong-sheng Zhang","doi":"10.1039/DC9898700013","DOIUrl":"https://doi.org/10.1039/DC9898700013","url":null,"abstract":"Pure MgO samples having greatly different morphologies and lithium-promoted catalysts derived from these materials have been examined by electron microscopy. In addition, their ability to generate and react with gas-phase methyl radicals has been determined using e.s.r. in combination with a matrix-isolation technique. Lithium caused the MgO to sinter severely at 700 °C, but the resulting material showed improved activity for the generation of methyl radicals. These factors gave rise to catalysts which were moderately active and selective for the oxidative dimerization of CH4 at 700 °C (up to 20% conversion, 66% C2+ selectivity). The results are particularly significant in that catalysts which had been prepared such that the lithium was initially present as Li2O on the surface exhibited almost constant C2+ production as the Li2O was converted to Li2CO3. Thus, neither Li2O nor Li2CO3 is the active phase for the selective conversion of CH4. A catalyst prepared from Li2CO3 and MgO sintered much less extensively, produced more CH3˙ radicals and gave higher yields of C2+ hydrocarbons. A comparison of these catalytic properties suggests that surface area and related morphological factors do not have an adverse effect on the oxidative dimerization reaction, provided the surface can be rendered inert to secondary reactions with methyl radicals.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"72 1","pages":"13-21"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85778086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
W. Albery, Zhengshi Chen, B. Horrocks, A. Mount, P. J. Wilson, D. Bloor, Andrew T. Monkman, C. M. Elliott
Experimental results from electrochemical e.s.r. on electrodes modified with conducting polymers such as polyaniline, polypyrrole and polythiophene are presented. The results show that the polymer exists in two forms, one stable when it is insulating (α) and the other (β) when it is conducting. In the conducting region the kinetics of the transformation of the metastable α form into the β form can be followed by e.s.r. It is further shown that in the lightly oxidised films there is a one-to-one correlation between charge injected and e.s.r. spins. These results are explained by a chemical redox model as opposed to a delocalised band.Results from a.c. impedance studies are presented. These results are explained by an equivalent circuit which includes a novel transmission line with differential resistances. Theoretical impedance plots are derived. Experimental results show that the polymer resistance and the resistance of the aqueous pores are equal. Reasons for this finding are discussed.
{"title":"Spectroscopic and electrochemical studies of charge transfer in modified electrodes","authors":"W. Albery, Zhengshi Chen, B. Horrocks, A. Mount, P. J. Wilson, D. Bloor, Andrew T. Monkman, C. M. Elliott","doi":"10.1039/DC9898800247","DOIUrl":"https://doi.org/10.1039/DC9898800247","url":null,"abstract":"Experimental results from electrochemical e.s.r. on electrodes modified with conducting polymers such as polyaniline, polypyrrole and polythiophene are presented. The results show that the polymer exists in two forms, one stable when it is insulating (α) and the other (β) when it is conducting. In the conducting region the kinetics of the transformation of the metastable α form into the β form can be followed by e.s.r. It is further shown that in the lightly oxidised films there is a one-to-one correlation between charge injected and e.s.r. spins. These results are explained by a chemical redox model as opposed to a delocalised band.Results from a.c. impedance studies are presented. These results are explained by an equivalent circuit which includes a novel transmission line with differential resistances. Theoretical impedance plots are derived. Experimental results show that the polymer resistance and the resistance of the aqueous pores are equal. Reasons for this finding are discussed.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"28 1","pages":"247-259"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81042573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Hillman, David C. Loveday, M. Swann, R. M. Eales, A. Hamnett, S. Higgins, S. Bruckenstein, C. Wilde
The electrochemical quartz crystal microbalance (EQCM) and ellipsometry have been used to study directly the movement of ions and solvent into/out of electroactive polymer films. The systems studied were polyvinylferrocene (PVF), polybithiophene (PBT) and polythionine (PTh). The overall mass changes accompanying oxidation/reduction indicate that film sources of counter-ions (required to maintain electroneutrality) can be significant. The extent of participation of these species depends on the nature and concentration of the bathing electrolyte solution. In the case of PVF, optical data also indicate a structural change: reduced PVF appears to be a homogeneous compact film, whilst oxidised PVF+ is a more diffuse, inhomogeneous film, whose polymer content decreases with distance from the electrode. Voltammetric experiments at rapid (and in some cases even moderate) scan rates show that transport of mobile species can be quite slow. It was generally observed that ingress into the polymer was slower than egress of the same species from the polymer. Charged species, notably proton in hydrated systems, move faster than neutral species, such as solvent, due to the influence of the field.
{"title":"Charge transport in electroactive polymer films","authors":"A. Hillman, David C. Loveday, M. Swann, R. M. Eales, A. Hamnett, S. Higgins, S. Bruckenstein, C. Wilde","doi":"10.1039/DC9898800151","DOIUrl":"https://doi.org/10.1039/DC9898800151","url":null,"abstract":"The electrochemical quartz crystal microbalance (EQCM) and ellipsometry have been used to study directly the movement of ions and solvent into/out of electroactive polymer films. The systems studied were polyvinylferrocene (PVF), polybithiophene (PBT) and polythionine (PTh). The overall mass changes accompanying oxidation/reduction indicate that film sources of counter-ions (required to maintain electroneutrality) can be significant. The extent of participation of these species depends on the nature and concentration of the bathing electrolyte solution. In the case of PVF, optical data also indicate a structural change: reduced PVF appears to be a homogeneous compact film, whilst oxidised PVF+ is a more diffuse, inhomogeneous film, whose polymer content decreases with distance from the electrode. Voltammetric experiments at rapid (and in some cases even moderate) scan rates show that transport of mobile species can be quite slow. It was generally observed that ingress into the polymer was slower than egress of the same species from the polymer. Charged species, notably proton in hydrated systems, move faster than neutral species, such as solvent, due to the influence of the field.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"75 1","pages":"151-163"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83800843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polypyrrole (PPy) and poly-N-methylpyrrole (PMPy) films have been prepared on electrodes in NaCl, polystyrenesulphonate (PSS), and dodecylsulphate (ROSO3–) electrolytes. The redox-switching of these coatings has been studied, mainly in NaCl electrolytes. At various electrode potentials the coated electrodes were withdrawn from the solutions to determine the composition of the films. Volta potential measurements, were conducted to obtain information on the Donnan potential. Based on these measurements, the effect of the negative fixed charge groups incorporated into the PPy or PMPy matrix on the membrane properties of the films was analysed. The anion exchange, cation exchange, and neutral states of the various coatings are defined over a range of electrode potentials. In one situation (PPy/PMPy/ROSO3–), the reversible and complete electrochemical redox transition between anion- and cation-exchange character is demonstrated.
{"title":"The effect of incorporated negative fixed charges on the membrane properties of polypyrrole films","authors":"C. Zhong, K. Doblhofer, G. Weinberg","doi":"10.1039/DC9898800307","DOIUrl":"https://doi.org/10.1039/DC9898800307","url":null,"abstract":"Polypyrrole (PPy) and poly-N-methylpyrrole (PMPy) films have been prepared on electrodes in NaCl, polystyrenesulphonate (PSS), and dodecylsulphate (ROSO3–) electrolytes. The redox-switching of these coatings has been studied, mainly in NaCl electrolytes. At various electrode potentials the coated electrodes were withdrawn from the solutions to determine the composition of the films. Volta potential measurements, were conducted to obtain information on the Donnan potential. Based on these measurements, the effect of the negative fixed charge groups incorporated into the PPy or PMPy matrix on the membrane properties of the films was analysed. The anion exchange, cation exchange, and neutral states of the various coatings are defined over a range of electrode potentials. In one situation (PPy/PMPy/ROSO3–), the reversible and complete electrochemical redox transition between anion- and cation-exchange character is demonstrated.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"90 1","pages":"307-316"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73650340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Theoretical constructs are developed for discussing diffusivity and conductivity in polymer ionic materials. Such materials are characterized by extensive disorder, either static (lack of long-range order) or static and dynamic (lack of long-range order with short-range order evolving with time). Beginning with a dynamic percolation model, we show that, in general, so long as the mean-square displacement of the charged particle obeys a certain growth law, the observed charged-particle motion will be diffusive, both in the ballistic regime, corresponding to electronic motion with strong scattering, and in the ionic-hopping regime, corresponding to dynamic disorder renewal of the hopping situation. Some general behaviour for transport under these conditions is predicted, including definite statements about the frequency dependence of the conduction, the relationship between the growth law in a single interval and the growth law for observation times long compared to scattering or renewal times, and the behaviour in the neighbourhood of the percolation threshold for the static problem. Interpretations are suggested both for ion and electron-hopping situations.A statistical thermodynamic model is developed for analysis of contact ion pair formation and its effect on conductivity in ion-conducting polymer systems. In this model, the energy (due to solvation and polarization) favouring formation of a homogeneous complex in which the cations are solvated by the polymer host, competes with an entropic term favouring the separated structures (free polymer and contact ion pairs). We derive general conditions for this phase separation, and an expression for the number of polymer-bound, homogeneously solvated ions. We show that this number will, in general, decrease monotonically with increase in temperature, due to entropic favouring of the phase-separated material, this is reminiscent of the lower consolute temperature phenomenon in liquid mixtures.
{"title":"Conductivity in polymer ionics. Dynamic disorder and correlation","authors":"M. Ratner, A. Nitzan","doi":"10.1039/DC9898800019","DOIUrl":"https://doi.org/10.1039/DC9898800019","url":null,"abstract":"Theoretical constructs are developed for discussing diffusivity and conductivity in polymer ionic materials. Such materials are characterized by extensive disorder, either static (lack of long-range order) or static and dynamic (lack of long-range order with short-range order evolving with time). Beginning with a dynamic percolation model, we show that, in general, so long as the mean-square displacement of the charged particle obeys a certain growth law, the observed charged-particle motion will be diffusive, both in the ballistic regime, corresponding to electronic motion with strong scattering, and in the ionic-hopping regime, corresponding to dynamic disorder renewal of the hopping situation. Some general behaviour for transport under these conditions is predicted, including definite statements about the frequency dependence of the conduction, the relationship between the growth law in a single interval and the growth law for observation times long compared to scattering or renewal times, and the behaviour in the neighbourhood of the percolation threshold for the static problem. Interpretations are suggested both for ion and electron-hopping situations.A statistical thermodynamic model is developed for analysis of contact ion pair formation and its effect on conductivity in ion-conducting polymer systems. In this model, the energy (due to solvation and polarization) favouring formation of a homogeneous complex in which the cations are solvated by the polymer host, competes with an entropic term favouring the separated structures (free polymer and contact ion pairs). We derive general conditions for this phase separation, and an expression for the number of polymer-bound, homogeneously solvated ions. We show that this number will, in general, decrease monotonically with increase in temperature, due to entropic favouring of the phase-separated material, this is reminiscent of the lower consolute temperature phenomenon in liquid mixtures.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"43 1","pages":"19-42"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76721722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Experimental data on the electrical conductivity of conducting polymers is reviewed. Polyacetylene is regarded as a prototype and the conductivity is studied as a function of doping level, temperature, frequency and conjugation length. The consistency of the data with a model of anisotropic variable range hopping is pointed out, with the exception of very highly doped samples, where in addition to hopping also temperature-independent tunnelling between large conducting domains has to be assumed.
{"title":"Charge transport in conducting polymers","authors":"S. Roth, H. Bleier, W. Pukacki","doi":"10.1039/DC9898800223","DOIUrl":"https://doi.org/10.1039/DC9898800223","url":null,"abstract":"Experimental data on the electrical conductivity of conducting polymers is reviewed. Polyacetylene is regarded as a prototype and the conductivity is studied as a function of doping level, temperature, frequency and conjugation length. The consistency of the data with a model of anisotropic variable range hopping is pointed out, with the exception of very highly doped samples, where in addition to hopping also temperature-independent tunnelling between large conducting domains has to be assumed.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"20 1","pages":"223-233"},"PeriodicalIF":0.0,"publicationDate":"1989-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83176360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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