Electroactive, or 'conductive', polymers are a rapidly expanding area of research with proposed applications ranging from batteries or electronic circuitry to artificial muscles and actuators. An emerging application for these materials is as constituents of corrosion resistant coatings. An important factor in any corrosion resistant coating is the level of porosity it possesses. Minimisation of porosity may be highly desirable for the production of highly protective films. This work aims to study methods for controlling the porosity of polypyrrole films for their possible use as corrosion resistant coatings. It has been observed that surfactants can modify the structure and morphology of polypyrrole on inert substrates such as platinum or indium-tin oxide glass, and on the non-inert substrate mild steel. This has involved the study of the conditions necessary for polymer deposition on mild steel where the tendency for metal dissolution competes with the polymerisation reaction. Corrosion studies were carried out, firstly, to assess the corrosion potentials for such films and, secondly, via Tafel extrapolation to determine the effects of film thickness and anionic surfactant concentration on the corrosion rates obtained. Further corrosion studies were performed on polypyrrole films with additions of molybdate corrosion inhibitor species and anionic surfactants. It was found that polypyrrole with additions of anionic surfactants had little or no effect on the corrosion characteristics of mild steel in saline environments. However, in the presence of molybdate and certain levels of surfactants, excellent corrosion resistance characteristics were observed. It is proposed that the reduction of polypyrrole occurs at large negative corrosion potentials, resulting in the formation of an insulating polymer film that is incapable of acting as a site for displaced corrosion reactions around which many of the theories of electro active polymer corrosion protection have previously been based.

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Neste trabalho são elaborados biossensores para a detecção amperométrica de glicose. Para isso, imobilizou-se a enzima glicose oxidase em matrizes de polímeros condutores. Foram construídos sensores utilizando-se poli(pirrol) e poli(N-metilpirrol). Com o objetivo de substituir o oxigênio molecular na etapa de transdução do sinal, o ferroceno foi incorporado dentro do polímero condutor. Para isso, os polímeros foram elaborados utilizando misturas água-etanol como meio de polimerização. A inclusão do ferroceno no sensor resulta em maior sensibilidad à glicose (4,33 µA Mm-1 cm-2 para o biossensor preparado a partir da mistura água-etanol contendo o ferroceno e de 0,23 µA mM-1 cm-2 para o sensor sem ferroceno ). Por outro lado, permite o funcionamento do sensor a potenciais menores que no caso do sensor sem ferroceno (0,4 V para o sensor com ferroceno vs. 0,65 V para o caso sem ferroceno). O deslocamento do potencial de detecção para valores menos positivos não foi suficiente para evitar as interferências causadas pelos íons ascorbato e ureato. Para isto, mostrou-se 100% efetivo o recobrimento dos sensores com uma película de Nafion®. A sobreoxidação do poli(pirrol) também mostrou potencialidade para a eliminação de interferentes, embora o processo resulte na perda de sensibilidade, provavelmente causada pela desnaturação da enzima. Quando usado o poli(N-metilpirrol) como suporte para a enzima, obtiveram se melhores respostas, causadas pela possibilidade de se preparar filmes mais espessos, consequentemente de imobilizar maior quantidade de enzima, sem observar perda de resposta causada por problemas difusionais. / The present work describes the elaboration of a biosensor for glucose detection. The enzyme, glucose oxidase, was immobilized in different conducting polymers. Two different polymers were used: polypyrrole and poly(N-methilpyrrole ). With the aim of replacing the molecular oxygen in the transduction step, ferrocene has been immobilized within the conducting polymer. Once the ferrocenium was insoluble in water, in order to develop a different route, the electropolymerization was carried out in a mixture of water and ethanol (1:1). This procedure leads to a polymer with a poor electroactivity, detected by Raman experiments. The ferrocene addition in the sensor increases the sensitivity to the glucose determination (4,33 µA mM-1 cm-2 for the biosensor with ferroecene and 0,23 µA mM-1 cm-2 for the sensor without ferrocene). Alternatively, the sensor containing ferrocene allows to operate at less positive potentials than that one without ferrocene (+ 0,40 V and + 0,65 V, respectively). This potential shift was not enough to inhibit the interference caused by ascorbate and ureate ions. One method to avoid the interference problem was to recover the sensor with a very thin layer of Nafion. Also poly(pyrrole) overoxidation is a very efficient method to eliminate this interference, but this process leads to a sensitivity decrease dueto enzyme denaturation. A better response was observed for sensor assembled using the poly(Nmethyl-pyrrole) as the support for enzyme immobilization. This behavior was provoked by the thicker of polymer film formed leading to higher amount of immobilized enzyme. Even though, no diminution in the response was caused by diffusion problems.

Neste trabalho investigamos o transporte eletrônico em dispositivos com estrutura ITO(óxido de estanho dopado com índio)/TiO2(dióxido de titânio)/RRP3HT(poli(3-hexiltiofeno)-regiorregular)/Al através de medidas de resposta espectral de fotocorrente, iluminando os dispositivos ora pelo eletrodo de ITO ora pelo de alumínio. O polímero RRP3HT é um politiofeno regiorregular e exibe uma atividade fotovoltaica relativamente alta. Os filmes de TiO2 e RRP3HT foram obtidos por spin-coating, sendo o óxido depositado a partir de uma dispersão coloidal de nanopartículas e o polímero a partir de uma solução de clorofórmio. O eletrodo de Al foi evaporado termicamente sobre o filme de polímero. As medidas de fotocorrente foram realizadas com o uso de uma lâmpada de Xe de 450W e de um monocromador e, depois de diversas medidas tendo a temperatura e a voltagem aplicada como parâmetros, obtivemos uma grande quantidade de importantes dados elétricos sobre os dispositivos. Dependendo das condições experimentais observamos diferentes respostas de fotocorrente: simbática ou antibática. Um modelo baseado em mecanismos de recombinação e na fotogeração de cargas, incluindo o perfil de absorção do RRP3HT, permitiu a obtenção de parâmetros elétricos importante em aplicações desse polímero a dispositivos fotodetectores e células solares. / In this work we investigated electronic transport phenomena in an ITO/TiO2/RRP3HT/Al structure using photoconductivity spectral response when devices were illuminated either by the ITO electrode or by the aluminum. RRP3HT is the regioregular poly(3-hexylthiophene), a polymer that exhibits a relatively strong photovoltaic activity. RRP3HT were dissolved in a solution of chloroform and nanoparticles of TiO2 were used in a colloidal dispersion. Both thin films of TiO2 and P3HT were deposited by spin coating technique over a commercial glass covered with ITO, and Al electrode was vacuum evaporated. Photoconductivity measurements were carried out making use of a Xenon lamp of 450 W and a monochromator to produce a single spectral line. After several measurements, having temperature and constant applied voltage as parameters, we obtained a great amount of important electrical data for the devices. Depending on the experimental conditions we obtained different photocurrent response, i. e. symbatic or antibatic. A model based on recombination mechanisms and photogenerated charges, including the absorption profile of the RRP3HT, allowed us to get some electrical parameters that are important for photovoltaic and photoconductive applications.

Philosophiae Doctor - PhD / Nitric oxide (NO) plays a key role as biological messenger in the biological system, however detection and quantification thereof has always posed significant problems. NOx is a principal constituent of air pollutants. There are seven oxides of nitrogen of which N2O, NO and NO2 are most important. NO is a free radical and reacts extremely fast with oxygen, peroxides and superoxides. It’s these reactions which are responsible for NO’s fleeting existence. The specific detection and quantification of NO still remains challenging. Most techniques rely on the measurements of secondary nitrite and nitrate species. Electrochemical techniques using ultra micro-electrode systems presented the possibility of direct detection of NO, offering a range of favourable characteristics; good selectivity towards NO, good sensitivity, fast response, long-term stability and ease of handling. Electrochemical detection of NO relies on the modification of electrode surfaces and exploiting the redox properties of NO. NO can either be oxidized or reduced electrochemically depending on the nature of the solution. Under cathodic current NO is reduced to nitrosyl, a highly unstable derivative of NO. These nitrosyls are subject to a serious of chemical reactions to eventually form nitrous oxide. Due to the interferences presented by the electrochemical reduction of NO, the electro oxidation of NO is therefore the methodology of choice for NO detection. The electrochemical oxidation of NO occurs at positive potentials around 800 mV vs. Ag/AgCl. However this potential range is not only favourable to NO oxidation but can lead to the oxidation of several other biological species. These interfering species are biologically present at concentrations higher than NO therefore selectivity is of the highest order when designing these electrode systems. Some nitric oxide sensors are limited in their sensitivity, stability and reproducibility. Direct electron transfer between redox proteins and conductive membrane layers has been scrutinized for years in an attempt to reproduce the mechanistic charge transfer processes for sensor application. However, literature reports have presented many arguments on the complexities associated with depositing these enzymes on electrode surfaces for the purpose of reproducing direct electron transfer at metalloprotein centres. The study sets out to design a material which could mimic the electrochemistry of denatured cytochrome-c. To achieve this it was imperative to design a polymer which could reproduce the electrochemistry of the ligands coordinated to the metal centre of the metalloprotein. A novel Schiff base was synthesized by cross-linking naphthalene to pyrrole to produce the monomer, N,N-bis((1H-pyrrol-2-yl)methylene)naphthalene-2,3-diamine). The monomer was electrodeposited on a screen print carbon electrode (SPCE) vs. Ag/AgCl and served as a supporting layer for denatured cytochrome-c. Cytochrome-c is classified as a metalloprotein. These metalloproteins possess metal centres which when denatured unfolds and allows access to the metal centre. Cytochrome-c was subjected to thermal denaturation which opened up the iron centre. The denatured metalloprotein was cross-linked to the ligand to reconstruct the heme centre environment. This was believed to facilitate the electrochemical activity of the system and allow for electrochemical analysis of these metalloproteins for sensor application. The redox behaviour of the sensors were modelled in phosphate buffer solution (PBS) with cyclic voltammetry. Electrochemical analysis reported the sensors to possess reversible electrochemistry with diffusion control characteristics. The sensor recorded a redox system in the negative potentials range. Following the establishment of the electrochemical profile of the sensor an attempt was made to produce a synthetic analogue of denatured cytochrome-c. Iron (II) was chelated to the monomer N,N-bis((1H-pyrrol-2-yl)methylene)naphthalene-2,3-diamine) to form an iron ligand complex. The complex was subjected to a series of characterization techniques which confirmed coordination to the metal centre. The iron ligand complex was electrodeposited on a SPCE over the potential window of -1 V and 1 V to model the electrochemical behaviour of the sensor. The material was found to be electroactive. Subsequent electrochemical analysis revealed the system to have electrochemical properties, analogous to that of the denatured cytochrome-c system. The sensor was applied in NO and NO2 studies and displayed an affinity towards NO. Based on extrapolated values it was postulated that the lower limit range for NO detection was in the range of 30 to 40 nM. The potentials recorded were lower than the reported oxidation potentials for nitric oxide. The sensor displayed stability and selectivity towards nitric oxide within a complex matrix. The complex matrix employed in this study was synthetic urine that was synthesised in the lab. The sensor displayed the capacity for linear range of NO detection with very low error margins. / 2021-09-01

Electroactive polymers (EAP) are an emerging branch of smart materials that possess the capability to change shape in the presence of an electric field. Opportunities for the advancement of knowledge were identified in the branch of EAP consisting of inherently electrically conductive polymers. This dissertation explores methods by which the unique properties of composite materials having conductive polymers as a constituent may be exploited. Chapter 3 describes the blending of polyaniline with conventional thermoplastics. Processing these polyblends into foams yielded a porous conductive material. The effect of blend composition and processing parameters on the resulting porous morphology and electrical conductivity was investigated. These findings represent the first systematic study of porous conductive polymer blends. In Chapter 4, multilayer electroactive polymer actuators consisting of polypyrrole films electropolymerized on a passive polymer membrane core were harnessed as actuators. The membrane is vital in the transport of ionic species and largely dictates the stiffness of the layered configuration. The impact of the mechanical properties of the membrane on the actuation response of polypyrrole-based trilayer bending actuators was investigated. Candidate materials with distinct morphologies were identified and their mechanical properties were evaluated. These results indicated that polyvinylidene difluoride membranes were superior to the other candidates. An electrochemical synthesis procedure was proposed, and the design of a novel polymerization vessel was reported. These facilities were utilized to prepare actuators under a variety of synthesis conditions to investigate the impact of conductive polymer morphology on the electromechanical response. Characterization techniques were implemented to quantitatively assess physical and electrochemical properties of the layered composite. Chapter 5 proposes a new unified multiphysics model that captures the electroactive actuation response inherent to conductive polymer trilayer actuators. The main contribution of this investigation was the proposal and development of a new hybrid model that unifies concepts from charge transport and electrochemomechanical models. The output of the proposed model was compared with published data and shown to be accurate to within 10%. Finally, Chapter 6 demonstrated the application of these materials for use as precision mirror positioners in adaptive optical systems.

Previous studies of the redox states of linear conjugated oligomers as models for polarons and bipolarons in conjugated polymers do not fully address the influence of intermolecular interactions on the electronic structure of conjugated systems in the solid state. Fusion of oligothiophenes onto a bicyclo[4.4.1]undecane core holds the conjugated oligomers in a permanent cofacial stack. One- and two-electron oxidation of the stacked oligomers affords mono(radical cation)s and dications that serve as models for polarons and bipolarons in p-doped conjugated polymers and demonstrates the effect of pi-stacking on the electronic structure of these species. Installation of phenyl-capped and ferrocenyl-capped oligothiophenes allows us to systematically vary pi-stacked oligomers and study intramolecular charge migration in other linear conjugated molecules.

Human disease processes are often characterized by a deviation from the normal physiological concentration of critical biomarkers. The detection of disease biomarkers requires the development of novel sensing methods which are sensitive, specific, efficient and low-cost. To address this need, a novel conductive and recognitive hydrogel composite material has been developed. This work investigated the fabrication methods, the chemical and physical composition, the sensing capabilities, and the biocompatibility of the proposed conductive and recognitive hydrogel composite materials. The conductive polymer was found to respond by changing conductivity in the presence of biomolecules. Specificity can then be incorporated into the system by integrating the conductive polymer with a molecularly imprinted hydrogel. The demonstration of a conductive and recognitive hydrogel composite is a step towards the integration of these materials into close-loop sensing and drug delivery systems. / text

Electroactive polymers (EAP) are an emerging branch of smart materials that possess the capability to change shape in the presence of an electric field. Opportunities for the advancement of knowledge were identified in the branch of EAP consisting of inherently electrically conductive polymers. This dissertation explores methods by which the unique properties of composite materials having conductive polymers as a constituent may be exploited. Chapter 3 describes the blending of polyaniline with conventional thermoplastics. Processing these polyblends into foams yielded a porous conductive material. The effect of blend composition and processing parameters on the resulting porous morphology and electrical conductivity was investigated. These findings represent the first systematic study of porous conductive polymer blends. In Chapter 4, multilayer electroactive polymer actuators consisting of polypyrrole films electropolymerized on a passive polymer membrane core were harnessed as actuators. The membrane is vital in the transport of ionic species and largely dictates the stiffness of the layered configuration. The impact of the mechanical properties of the membrane on the actuation response of polypyrrole-based trilayer bending actuators was investigated. Candidate materials with distinct morphologies were identified and their mechanical properties were evaluated. These results indicated that polyvinylidene difluoride membranes were superior to the other candidates. An electrochemical synthesis procedure was proposed, and the design of a novel polymerization vessel was reported. These facilities were utilized to prepare actuators under a variety of synthesis conditions to investigate the impact of conductive polymer morphology on the electromechanical response. Characterization techniques were implemented to quantitatively assess physical and electrochemical properties of the layered composite. Chapter 5 proposes a new unified multiphysics model that captures the electroactive actuation response inherent to conductive polymer trilayer actuators. The main contribution of this investigation was the proposal and development of a new hybrid model that unifies concepts from charge transport and electrochemomechanical models. The output of the proposed model was compared with published data and shown to be accurate to within 10%. Finally, Chapter 6 demonstrated the application of these materials for use as precision mirror positioners in adaptive optical systems.

Made available in DSpace on 2014-06-11T19:35:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2004Bitstream added on 2014-06-13T20:06:21Z : No. of bitstreams: 1 chaker_ja_dr_araiq.pdf: 4471758 bytes, checksum: 44afb42e6a0e98b7d57c6d4412d9ff10 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Materiais híbridos orgânicos-inorgânicos são materiais bifásicos onde a interpenetração das fases em uma escala nanométrica permite preparar materiais com propriedades inéditas. Este é o caso dos eletrólitos sólidos transparentes siloxano-poli(propileno óxido) estudados neste trabalho de doutorado. Este trabalho visou estabelecer correlações entre as propriedades de condução iônica e as características estruturais destes híbridos que são preparados pelo processo sol-gel. Os objetivos específicos propostos no projeto original incluem os seguintes itens: (a) estabelecer correlações entre a estrutura e as propriedades determinantes da condutividade iônica; (b) analisar a estrutura local do dopante, sua localização no sistema, e assim determinar os sítios de adsorção bem como sua participação na formação da ligação O-Na-O ou O-K-O envolvendo oxigênios tipo éter da cadeia polimérica; (c) determinar o efeito da retração e da formação de domínios com correlação espacial em função dos diferentes sais dopantes estudados sobre as propriedades de condução iônica; (d) comparar as propriedades e estrutura dos híbridos preparados com polímeros de diferentes massas moleculares e concentrações de dopante. Para isto, estudos das propriedades microestruturais, foram realizados através das técnicas de espalhamento de raios X, e análises da estrutura local por absorção de raios X (XANES e EXAFS), e RMN 23Na e 19F, corroborados com as propriedades de condução iônica dos materiais, além de medidas de espectroscopia Raman. Foram estabelecidas diversas correlações entre a estrutura e as propriedades dos materiais. Foi verificado, para amostras dopadas com KCF3SO3, que as amostras mais condutoras são aquelas que possuem um maior número de oxigênios ao redor do potássio. Paralelo... / Siloxane-poly(oxi propylene) (PPO) or Siloxane-poly(oxi propylene) hybrid materials prepared by the sol-gel route show increasing scientific and technological interest due to its particular structure in which the polymer chains are grafted to the inorganic nanoparticules. When doped with alkaline salts these hybrids present ionic conductivity similar to that of ionic conductive polymers (10-4 S/cm), and both their mechanical and optical properties are improved. However, the nature of the mobile species, are responsible for ther conductivity (free ions, ion-pairs, aggregates) is not well established. So that the knowledge of the nature and the local structure around the mobile ions is the challenger to improve the ionic properties. The ain of this work was to establish the correlations between the local structure around the charge carriers (coordination shell, solvation sphere) and the macroscopic conductivity. To reach this objective the local structure was probed by X ray absorption (XANES and EXAFS), Raman and NMR spectroscopy and the results related to that obtained from conductivity measurements.