Das Ziel der vorliegenden Arbeit ist die bessere Verarbeitung von Polyanilin (PANI), da dies bisher ein großer Nachteil unter leitfähigen Polymeren war. Dazu wird ein sperriges Tensid und Dotand, Dodecylbenzensulfonsäure (DBSA) verwendet. Zur Synthese der PANI kommen zwei verschiedene Methoden zur Anwendung, die in dieser Dissertation in zwei Kapiteln beschrieben werden. Im ersten Teil wurden in einem kleinen Reaktionsvolumen (250 mL) PANI-DBSA-Suspensionen synthetisiert, wobei mit einem binären Gemisch aus 2-Propanol und Wasser als Lösungsmittel gearbeitet wird um die Löslichkeit zu unterstützen. Die micellenunterstützte Synthese produziert grüne Dispersionen, welche nach länger als einem Jahr noch keine sichtbare Ausscheidung zeigen. Eine detaillierte spectroelektrochemische Untersuchung der PANI-DBSA-Nanokolloide wurde durchgeführt und gibt eine bessere Erklärung der Charge-Transfer-Prozesse zwischen PANI-Kolloiden und Elektrodenoberfläche. In einem alkalischen Medium ist das UV-Vis-Spektrum von der Beweglichkeit der Anionen und von einem elektrokinetischen Phänomen abhängig. Um den „metal-to-insulator”-Übergang zwischen PANI-Kolloiden, welcher durch pH-Wert-Änderung des Mediums geschehen kann, zu zeigen, wurden UV-Vis- und pre-resonanz-Raman-Spektroskopie verwendet. Im zweiten Teil der Dissertation wird zur Polymerisation von Anilin sowie seinen Copolymeren mit o-Toluidin eine neue Technik der Polymerisation beschrieben, welche durch inverse Emulsion erfolgt. Diese benutzt Benzoylperoxid, ein ungewöhnlicheres organisches Oxidationsmittel. Die erhaltenen PANI sind in gebräuchlichen organischen Lösungsmitteln, wie in Chloroform, vollständig löslich. Mit einer klar-transparenten, grünen Lösung von PANI können metallische Oberflächen oder Glas leicht tropfenbeschichtet werden. Zyklische Voltammetrie und spektroelektrochemische Verfahren kamen zum Einsatz, um die Elektroaktivität, das UV-Vis-Verhalten und die „metal-to-insulator”-Übergänge der chemisch synthetisierten PANI als Funktion des verwendeten Elektrodenpotentials zu untersuchen. Die elektrische Leitfähigkeit der Materialien ist relativ hoch (R = 10 ). SEM-Untersuchungen zeigen, dass die Menge des zugesetzten DBSA die Morphologie des Polymers stark beeinflusst. Aus in situ UV-Vis-spektroskopischen Messungen lässt sich eine gute elektrochromische Reversibilität des Polymers erkennen. DBSA kann Poly(o-toluidin) (POT) effektiv dotieren, auch wenn von der Methylgruppe eine sterische Hinderung ausgeht. Die spektroskopischen Untersuchungen, wie UV-Vis, FT-IR, Raman-Spektroskopie und zyklische Voltammetrie, zeigen deutlich, dass wirkliche Copolymere gebildet werden und die Möglichkeit von Kompositen nicht in Betracht kommt. Das entstandene Poly(anilin-co-o-toluidin) (PAT) ist in schwach polaren Lösungsmitteln wie Chloroform löslich. Wie erwartet, sind die elektrischen Leitfähigkeiten der Copolymere viel kleiner als die Leitfähigkeit von PANI-DBSA.

Una parte importante del trabajo desarrollado en la presente tesis está basado en la puesta a punto y aplicación de la técnica de la microscopía electroquímica de barrido (SECM). Con esta técnica se han caracterizado electroquímicamente superficies sobre las que se han sintetizado una serie de materiales electroactivos desarrollados por nuestro grupo de investigación. Dichos materiales se sintetizan sobre diferentes substratos con el fin de disponer de electrodos de trabajo con aplicación en el contexto del tratamiento electroquímico de aguas residuales contaminadas con colorantes azoicos, provenientes de procesos de tintura en industrias textiles. Entre las superficies desarrolladas se incluyen: ¿ Ánodos dimensionalmente estables (DSAs) fabricados a partir de una superficie de Ti recubierta de SnO2 (Ti/SnO2), dopada con Sb (Ti/SnO2-Sb) y estabilizada con Pt (Ti/SnO2-Sb-Pt). ¿ Un tejido de poliéster (PES) recubierto de polipirrol (PPy) dopado con antraquinona sulfonato (PES/PPy-AQSA) o fosfotungstato (PES/PPy- PW12O403-). ¿ Un tejido de PES recubierto de polianilina (PANI) sintetizada en medios sulfúrico (PES/PANI-HSO4-) y clorhídrico (PES/PANI-Cl-). ¿ Un hilo de Pt recubierto de PANI con Pt electrodispersado (Pt/PANI-Pt). ¿ Un tejido de fibra de carbono recubierto de PANI (C/PANI) con o sin Pt electrodispersado (C/PANI-Pt). ¿ Un tejido de PES recubierto con óxido de grafeno (GO) o con su forma reducida (RGO). Los análisis locales efectuados a las superficies anteriormente descritas permitieron determinar su electroactividad frente a los pares redox Fe(CN)63-/4- y Ru(NH3)63+/2+ seleccionados como mediadores. Las curvas experimentales de aproximación obtenidas con el sistema en modo feedback, se compararon con las curvas teóricas establecidas por la teoría SECM para un substrato conductor (feedback +) y un substrato aislante (feedback -). Las imágenes SECM en 2D y 3D permitieron observar la distribución de la actividad electroquímica superficial para las diferentes muestras. Los resultados obtenidos con la microscopía SECM se utilizaron para validar los procedimientos de síntesis del material electroactivo en lo concerniente a su electroactividad y a la homogeneidad de su distribución. Las superficies textiles presentan una topografía muy irregular en comparación con la superficie metálica de un DSA. Aspecto especialmente reseñable en las muestras textiles es la influencia que ejerce la topografía del substrato textil en la imagen SECM de la electroactividad con el microelectrodo moviéndose a altura constante con respecto al substrato. En este sentido, las imágenes SECM obtenidas sobre las muestras textiles muestran como la electroactividad superficial reproduce el patrón geométrico del tejido. La influencia en la actividad electroquímica de aspectos tales como: tiempo de vida útil/corrosión en el caso de los DSAs, tipo de dopante/pH en el caso de la superficie PES/PPy, influencia del pH en las muestras de PES/PANI, el estado de oxidación de la especie electroactiva y la influencia del mediador (par redox) en el caso del grafeno, ha quedado puesta de manifiesto claramente en los estudios efectuados con la microscopía SECM. Una segunda parte importante del trabajo realizado en la presente tesis, se desarrolla como continuación a los trabajos que el grupo de investigación viene realizando dentro del contexto del tratamiento electroquímico de colorantes azoicos en disolución acuosa. Así, en el capítulo 2 de la presente tesis, se estudia el desarrollo, caracterización y aplicación de una serie de electrodos fabricados a partir de un tejido activo de fibra de carbono. El objetivo que persigue el desarrollo de estos electrodos está en su aplicación a procesos industriales tales como: la electrooxidación de moléculas relativamente sencillas como por ejemplo metanol o, de acuerdo con nuestra línea de investigación, para el tratamiento electroquímico de aguas contaminadas con colorantes azoicos provenientes de los procesos de tintura en industrias textiles. Entre los electrodos textiles de fibra de carbono desarrollados en el capítulo 2 de la presente tesis se incluyen: ¿ Electrodos textiles de carbono sin modificar. ¿ Electrodos textiles de carbono modificados con Pt disperso. ¿ Electrodos textiles de carbono recubiertos de PPy o PANI. ¿ Electrodos textiles de carbono recubiertos de PPy o PANI con Pt disperso. Dos tipos de geometrías se eligieron a la hora de fabricar los electrodos de fibra de carbono anteriormente citados. Los electrodos monodimensionales (WE1D) fueron preparados a partir de una hebra tomada del propio tejido. Los electrodos bidimensionales (WE2D) se prepararon a partir de una banda de (1 cm x 3 cm) cortada del tejido de carbono. Por medio de la voltametría cíclica (CV) y utilizando los WE1D se establecieron las condiciones de síntesis para la fabricación de los WE2D modificados. Además, por medio de la CV se estudió la respuesta electroquímica de los WE1Ds en diferentes sistemas electroquímicos tales como: una disolución de H2SO4, una disolución de CH3OH/H2SO4 y una disolución de amarante/H2SO4. Para este último sistema, además, se utilizó un electrodo de carbono vítreo (GCE) ya que proporcionaba una respuesta voltamétrica más precisa que la obtenida con los WE1Ds. En la caracterización electroquímica que se realizó a los electrodos WE2D, la microscopía SECM jugó un papel relevante. Con la configuración 2D no era posible obtener voltagramas precisos que nos permitieran observar el comportamiento electroquímico de los diferentes WE2D modificados. Con la microscopía SECM, sí se pudo medir la actividad electrocatalítica de las diferentes superficies validándose, entonces, las condiciones de síntesis utilizadas. Algunas de estas condiciones, como los rangos de potencial, se habían establecido previamente para los WE1D. Así, la microscopía SECM se muestra como alternativa a la CV para la medida de la electroactividad superficial y de la distribución del material electrocatalítico para este tipo de muestras. Además de la caracterización electroquímica, se realizó también una caracterización morfológica de las superficies electródicas mediante la toma de imágenes por medio de la microscopía electrónica de barrido (SEM) y del microscopio estereoscópico. El estudio voltamétrico efectuado para el sistema amarante/H2SO4 con los electrodos textiles WE1D y el electrodo GCE permitió el establecimiento de los potenciales de trabajo a los que realizar la electrólisis de oxidación y de reducción a potencial controlado con los electrodos WE2D, WE2D/Pt y WE2D/PANI-Pt. Con los electrodos de trabajo anteriores, se llevan a cabo diferentes electrólisis de electroreducción y electrooxidación a una disolución de amarante en medio sulfúrico utilizando una célula en forma de ¿H¿ con separación de compartimentos. El seguimiento del proceso de degradación de la molécula de amarante y por ende de la decoloración de la disolución, se efectuó por medio de la cromatografía líquida de alta resolución (HPLC) y las espectroscopías UV-visible, fluorescencia de emisión e infrarroja por transformada de Fourier con reflexión total atenuada (FTIR-ATR). Los resultados de eficiencia obtenidos en las electrólisis confirman la elección de los potenciales de trabajo seleccionados. El porcentaje de decoloración tanto con las electroreducciones como con las electrooxidaciones se sitúa por encima del 90 %. También se comprobó que la presencia de platino trae consigo una significativa reducción del tiempo de electrólisis para la electrooxidación a 900 mV. Los análisis de los espectros UV, de fluorescencia de emisión y FTIR-ATR permitieron establecer diferencias significativas en relación con el tipo de proceso electroquímico (electroreducción/electrooxidación), tipo de electrodo (modificado/no modificado) y la presencia/ausencia de cloruros en el medio de reacción. Con este trabajo se establece una metodología de cara a futuros estudios con otros colorantes azoicos utilizando electrodos basados en el tejido de fibra de carbono. / Fernández Sáez, J. (2014). Análisis por microscopía electroquímica de barrido de superficies electroactivas y desarrollo-caracterización de electrodos basados en un tejido de fibra de carbono [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/38239 / Alfresco

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Today, smart innovation has become an essential part of human life; thus, contemporary technologies are always looking for intelligent, responsive, and efficient materials to satisfy these demands. Consequently, synthetic "metals" or, more precisely, intrinsically conducting polymers (CPs) have begun to find a place as valuable and practical materials for a new generation of devices. Amongst all intrinsic conducting polymers, polyaniline (PANI) has attracted significant attention due to its outstanding air and moisture stability, simple preparation technique, and high electrical conductivity (chapter I). Chapter II represents the synthesis of a new PANI derivative that contains a phenoxazine unit co-polymerized with p-phenylenediamine derivatives by the Buchwald/Hartwig reaction. These polymers are soluble in many common organic solvents, which permit their full characterization and allow for solution processing. The polymers' optical properties mimicked PANI; however, they were more electrochemically stable and soluble compared to PANI. In addition, the analogous PANI emeraldine base forms a large bathochromic shift in the absorption spectra upon acidic doping to form analogues of PANI emeraldine salts. Chapter III describes our strategy to prepare economical, electrochemically stable, and processable PANI derivatives from carbazole and 1,4-aryldiamines for supercapacitor device. The polymers exhibit good solubility in various organic solvents, enabling a scalable spray-coating method to fabricate electrodes. The polymers were used to fabricate electrodes for supercapacitor devices and exhibit a maximum area capacitance of 64.8 mF cm−2 and specific capacitance of 319 F g−1 at a current density of 0.2 mA cm−2. Chapter IV MXene has been recently widely applied to energy storage devices due to its metallic conductivity and excellent electrochemical Activities. However, MXene sheets suffer from the restacking phenomena during cycling. Restacking restricts the ion diffusions and storage capability between the MXene layers, which lowers the accessible surface area. The restacking phenomena of MXene sheets was shown to be eliminated by the deposition of conductive polymers on the surface of MXene sheets.

>Magister Scientiae - MSc / The aim of this study was to produce useful composite materials from fly ash, a major waste product of coal combustion from power plants. Polyaniline-fly ash (PANI-FA) composites were prepared by in situ polymerisation of aniline in the presence of Fly Ash (FA) by two slightly different methods. In one case polystyrene sulphonic acid (PSSA) was used as a stabilizer and in another case the starting materials (aniline and FA) were aged before oxidation. The aging procedure formed nanotubes that have cross-sectional diameters of 50-110 nm. The other procedure produced nanotubes with a diameter of 100-500 nm and the length of up to 10μm. The presence of metal oxides and silica in FA were responsible for the formation of nanorods in PANI-PSSA-FA.. The formation of the composites was confirmed by UV-Vis and FTIR. The UV-Vis showed maximum absorbance at 330-360 nm ( due to π-π* transition of benzoid rings) and 600-650 nm(due to charge transfer excitons of quinoid rings), which are characteristics of emaraldine base. The electrochemical analysis of the composites showed that the composites were conductive and electroactive. The Cyclic Voltammetry of PANI-PSSA-FA showed three redox couples which are characteristics of sulphonated PANI. The morphology of the composites was studied by Scanning Electron Microscopy (SEM) and showed that our methods gave composites with improved homogeneity as compared to other reported methods. Thermo Gravimetric analysis (TGA) showed that the presence of FA in the composites improves the thermal stability of the composites by up to 100 0C.

Capacitive deionization is a promising technology for purification and desalination of brackish water with great advantages over current technologies due to its low operating cost and high-water recovery ratio. Most of the system studied relies on the adsorption/desorption capacity of activated carbon electrodes due to its high surface area. However, its specific adsorption capacity is limited since the adsorption is predominantly on the surface of the electrodes. In this thesis we propose the use of polyaniline as a chloride-ion adsorption material. Polyaniline is a redox polymer able to accommodate anions in several of its three states when subjected to an external voltage. To this end, we synthesized polyaniline by electrodeposition technique and its electrochemical behavior was studied. A hybrid CDI system was assembled, using PANI as anode material and activated carbon cloth as cathode, showing outstanding adsorption of 37.26 mg/g Cl at current densities of 250 A/g. The energy consumption of this system was of 0.4979 kWh/m3. Its stability was evaluated over 50 cycles with negligible capacity loss. Along with its use in a CDI system, the aim of this thesis was to understand the mechanisms of operation of this material, by means of its physical and electrochemical characterization, as well as its efficiency and stability through the use of this material in capacitive deionization cells. / Kapacitiv avjonisering är en lovande teknik för rening och avsaltning av bräckt vatten med stora fördelar jämfört med nuvarande teknik på grund av dess låga driftskostnader och höga vattenåtervinningsgrad. De flesta av de studerade systemen bygger på adsorptions/desorptionskapaciteten hos elektroder av aktivt kol på grund av dess stora yta. Dess specifika adsorptionskapacitet är dock begränsad eftersom adsorptionen huvudsakligen sker på elektrodernas yta. I den här avhandlingen föreslår vi att polyanilin används som adsorptionsmaterial för kloridjoner. Polyanilin är en redoxpolymer som kan ta emot anjoner i flera av sina tre tillstånd när den utsätts för en extern spänning. För detta ändamål syntetiserade vi polyanilin genom elektrodepositionsteknik och dess elektrokemiska beteende studerades. Ett hybrid CDI-system monterades med PANI som anodmaterial och aktiverad kolduk som katod, vilket visade en enastående adsorption av 37,26 mg/g Cl vid en strömtäthet på 250 A/g. Energiförbrukningen för detta system var 0,4979 kWh/m3. Systemets stabilitet utvärderades över 50 cykler med försumbar kapacitetsförlust. Förutom användningen i ett CDI-system var syftet med denna avhandling att förstå detta materials funktionsmekanismer genom fysisk och elektrokemisk karakterisering samt dess effektivitet och stabilitet genom användning av detta material i kapacitiva avjoniseringsceller.

Corrosion protection performance of a completely soluble polyaniline-dodecylbenzenesulfonic acid salt (PANI-DBSA) on C45 steel has been studied with electrochemical impedance and potentiodynamic measurements. Chloroform is the most suitable solvent to process the pristine PANI-DBSA because of negligible interaction of the solvent with the polyaniline (PANI) backbone. An anodic shift in the corrosion potential (<img src="http://scitation.aip.org/stockgif3/Dgr.gif" alt="Delta" align="bottom" border="0"><i>E</i>=~70&nbsp;&nbsp;mV), a decrease in the corrosion current and a significant increase in the charge transfer resistance indicate a significant anti-corrosion performance of the soluble PANI deposited on the protected steel surface. Corrosion protection follows the mechanism of formation of a passive oxide layer on the surface of C45 steel. In situ UV-Vis spectroscopy was used to investigate the differences in permeability of aqueous anions into PANI-DBSA. Preliminary results of electron diffraction studies show that PANI-DBSA possesses an orthorhombic type of crystal structure. An increase in the feed ratio of DBSA to aniline increases the tendency of aggregation of spherical particles of PANI obvious in transmission electron microscopy. PANI-DBSA slowly loses its electrochemical activity in acid free electrolyte without undergoing degradation.

This thesis describes technical and scientific aspects of new types of composite films/coatings for corrosion protection of carbon steel, composite films with nanometer thickness consisting of mussel adhesive protein (Mefp‐1) and ceria nanoparticles, and polymeric composite coatings with micrometre thickness consisting of conducting polymer and ceria nanoparticles in a UV‐curing polyester acrylate (PEA) resin. The influence of microstructure on corrosion behaviour was studied for a Fe‐Cr‐V‐N alloy containing micro‐sized nitrides with different chemical composition spread in martensitic alloy matrix. The Volta potential mapping suggested higher relative nobility for the nitride particles than the alloy matrix, and the nitrides with higher amounts of nitrogen and vanadium exhibited higher nobility. Potentiodynamic polarization measurements in a 0.1 M NaCl solution at neutral pH and ambient temperature showed passivity breakdown with initiation of localized corrosion which started in the boundary region surrounding the nitride particles, especially the ones enriched in Cr and Mo. Mefp‐1/ceria nanocomposite films were formed on silica and metal substrates by layer‐by‐layer immersion deposition. The film formation process was studied in situ using a Quartz Crystal Microbalance with Dissipation (QCM‐D). The film grows linearly with increasing number of immersions. Increasing Mefp‐1 concentration or using Mefp‐1 with larger size leads to more Mefp‐1 being deposited. Peak Force Quantitative Nanomechanical Mapping (Peak Force QNM) of the composite films in air indicated that the elastic modulus of the film increased when the film deposited had a higher Mefp‐1 concentration. It was also noted that the nature of the outermost layer can affect bulk morphology and surface mechanical properties of the film. The QCM‐D study of Mefp‐1 on an iron substrate showed that Mefp‐1 adsorbs at a high rate and changes its conformation with increasing adsorption time. The QCM‐D and in situ Peak Force QNM measurements showed that the addition of Fe3+ ions causes a transition in the single Mefp‐1 layer from an extended and soft layer to a denser and stiffer layer. In situ ATR‐FTIR and Confocal Raman Microscopy (CRM) analyses revealed complex formation between Fe3+ and catechol groups in Mefp‐1. Moreover, optical microscopy, SEM and AFM characterization of the Mefp‐1/ceria composite film formed on carbon steel showed micron‐size aggregates rich in Mefp‐1 and ceria, and a nanostructure of well dispersed ceria particles in the film. The CRM analysis confirmed the presence of Mefp‐1/Fe complexes in the film. Electrochemical impedance microscopy and potentiodynamic polarization measurements showed that the Mefp‐1/ceria composite film can provide corrosion protection for carbon steel, and that the protection efficiency increases with exposure time. Composite coatings of 10 μm thickness composed of a UV‐curing PEA resin and a small amount of conductive polymer and ceria nanoparticles were coated on carbon steel. The conductive polymer (PAni) was synthesized with phosphoric acid (PA) as the dopant by chemical oxidative polymerization. The ATR‐FTIR and SEM analyses confirmed that the added particles were well dispersed in the coatings. Electrochemical measurements during long exposure in 0.1 M NaCl solution, including open circuit potential (OCP) and EIS, were performed to investigate the protective performance of the coatings. The results showed that adding ceria nanoparticles can improve the barrier properties of the coating, and adding PAni‐PA can lead to active protection of the coating. Adding PAni‐PA and ceria nanoparticles simultaneously in the coating can improve the protection and stability of the composite coating, providing excellent corrosion protection for carbon steel. / <p>QC 20131024</p>

Philosophiae Doctor - PhD (Chemistry) / Supercapacitors, also known as ultracapacitors or electrochemical capacitors, are considered one of the most important subjects concerning electricity or energy storage which has proven to be problematic for South Africa. In this work, graphene oxide (GO) was supported with platinum, silver and copper nanoparticles anchored with dodecylbenzenesulphonic acid (DBSA) doped polyaniline (PANI) to form nanocomposites. Their properties were investigated with different characterization techniques. The high resolution transmission electron microscopy (HRTEM) revealed GO's nanosheets to be light, flat, transparent and appeared to be larger than 1.5 ?m in thickness. This was also confirmed by high resolution scanning electron microscopy (HRSEM) with smooth surfaces and wrinkled edges observed with the energy dispersive X-ray analysis (EDX) confirming the presence of the functional groups such as carbon and oxygen. The HRTEM analysis of decorated GO with platinum, silver and copper nanoparticles (NPs) revealed small and uniformly dispersed NPs on the surface of GO with mean particle sizes of 2.3 ± 0.2 nm, 2.6 ± 0.3 nm and 3.5 ± 0.5 nm respectively and the surface of GO showed increasing roughness as observed in HRSEM micrographs. The X-ray fluorescence microscopy (XRF) and EDX confirmed the presence of the nanoparticles on the surface of GO as platinum, silver and copper which appeared in abundance in each spectra. Anchoring the GO with DBSA doped PANI revealed that single GO sheets were embedded into the polymer latex, which caused the DBSA-PANI particles to become adsorbed on their surfaces. This process then appeared as dark regions in the HRTEM images. Morphological studies by HRSEM also supported that single GO sheets were embedded into the polymer latex as composite formation appeared aggregated and as bounded particles with smooth and toothed edges.

For every phenomenon found in inorganic materials, organic counterparts have been found in the last 50 years. The discovery of metallic conductivity in the inorganic conjugated polymer (SN)x was a forerunner to the discovery of metallic conductivity in Polyacetylene [1]. It was soon followed by the development of Polypyrrole and Polythiophene, and by the rediscovery of Polyaniline as a conducting polymer [2]. In polymers like Polyacetylene and Polythiophene, doping is by a redox reaction where the incorporation of electron withdrawing groups creates charge carriers in the polymer backbone. In contrast to these polymers, the main doping mechanism in Polyaniline is protonation, that is the attachment of a proton (donated by an acid) to specific sites (imine and amine groups) in the polymer. The protonated groups are also the sites where water and oxygen interact with the charge carriers on the polymer chain. A wide variety of quasi-particle states (excitons, bipolarons, separated polarons and polaron lattice forms) exist in Polyaniline, in its different states of oxidation and protonation. All of them have different transport and optical signatures. Out of these, only the polaron lattice gives rise to a half-filled conduction band, and therefore a metallic state [3]. This fascinating interplay of protonation and metallic features in Polyaniline, combined with its easy processibility, has made Polyaniline an attractive conducting polymer. Therefore the main focus of this thesis is on the role of the dopant on the electronic and optical properties of doped Polyaniline. The first chapter describes the main features of Polyaniline and its doping by protonation. The second chapter describes the experimental and simulation methods used in this thesis. Steady improvements in processing have led to reduced disorder in the samples, and have given rise to stronger metallic features like metallic (Drude-like) reflectivity in the infrared frequencies, and a positive temperature coefficient of the logarithmic derivative of the conductivity. High molecular weight Polyaniline doped with sulfonic acid dopants by surfactant-counterion processing, like Polyaniline doped with AMPSA (2-acrylamido-2-methyl-1-propanesulfonic acid) [4] and cast from dichloroacetic acid (DCA), shows all the metallic features indicative of an intrinsic metallic state [5]. In this thesis, the third chapter describes the spin-charge dynamics of Polyaniline doped with AMPSA (PANIAMPSA) through X-band Electron Spin Resonance studies [6]. Electron Spin Resonance (ESR) is an important technique to probe the spin-charge dynamics of conducting polymers [7, 8]. The X-band ESR spectra of PANI doped with AMPSA showed the presence of two lines (one broad and one narrow) at all temperatures and doping levels, indicative of two types of spin carriers. Three interesting features were observed in our study: a large linewidth ( ~100 Gauss), a maximum of ESR linewidth at ~ 25 K, and a surprising independence of linewidth on water/O2 . The temperature dependence of both linewidths suggests that the broad line is due to the delocalised charge carriers in well-ordered regions, and that the narrow line is due to localised spins in the disordered regions in the sample. Although the XRD spectra showed minimal crystallinity, the ESR and SQUID susceptibility had a strong Pauli contribution, indicative of an intrinsic metallic state. A similarity of the temperature dependence of linewidths of PANI-AMPSA with MWNT-s and HOPG graphite suggested that some quasi-2-D (Q2D) ordering is present in PANI-AMPSA. From Semi-empirical molecular modelling studies, a plausible hydrogen bonding pattern is suggested that can give rise to the Q2D graphene-like arrangement of the PANI polymer chains. This ordering is due to hydrogen bonding between the acrylamido group of the dopant and the amine fragment of the Polyaniline backbone. Hydrogen bonds are not just structural linkers between adjacent chains; they can have subtle effects on electronic states of the polymer backbone due to charge transfer/withdrawal by the hydrogen bond from the delocalised β-electron system of the backbone. The same Q2D model is used to explain the water/oxygen independence of linewidth in PANI-AMPSA. The temperature dependence of linewidth of both lines has been explained in terms of the QTDG (Quasi Two Dimensional Graphite) model, where a strong exchange interaction is presumed to arise between the 2D delocalised charge carriers and the localised spins, leading to a low-temperature peak in the the linewidth. Water is known to significantly enhance the conductive properties of doped Polyaniline [9]. A detailed DFT (Density Functional Theory) modelling study of the influence of water in doped Polyanilines is presented, which clearly indicated that water enhances the charge transfer between the counterion and the polymer backbone. The torsion angles between the adjacent phenyl rings of the emeraldine base decrease when the imine nitrogens are protonated by inorganic acids like HCl and HBr, and hydration of the acid counterions further decrease the torsion angles. In contrast, the torsion angles of the AMPSA protonated Polyaniline are already low (comparable to the hydrated cases), and the charge transferred by AMPSA is also enhanced. Visualisation of the molecular structure of the PANI-AMPSA complex suggested that water molecules may play a minimal role in the electronic properties of AMPSA doped Polyaniline. We suggest the Q2D ordering as the reason for the temperature dependence of the linewidth, the lack of oxygen and water dependence of the linewidth, as well as the enhanced metallic properties in PANI-AMPSA, as compared to other doped Polyanilines. The electronic states of Polyaniline are modified by both redox processes and protonation. This gives rise to a wide variety of optical states, which can be easily accessed by both applied potential and pH [10]. Therefore Polyaniline displays strong electrochromism across the visible, near-IR (NIR), IR and even microwave spectral regions. This feature has wide applications in electrochromic devices. However, a fundamental understanding of the phenomena behind this electrochromism, the charge carrier(s) responsible, and the relation of nanoscopic morphology and electrochemical properties to the electrochromism, is still not clear. In the fourth chapter, we have analysed extensive data from electrochromic devices [11]. Clear assignments are that certain population states contribute predominantly to certain spectral regions (e.g. bipolaron states to the IR, the valence band to the visible and other mid-gap states to the microwave). Among more specific findings, a prominent 7µm (0.16 eV) peak in MIR devices is ascribed to bipolarons, while a low-energy transition at 0.054 eV is ascribed to inter/intra-chain transitions. Each of these transitions is tracked with respect to changes in applied potential, as well as correlated with device morphology and construction. Our analysis of UV-Vis-MIR-FIR-microwave results along with detailed SEM data clearly relates performance in different wavelength regions to morphology. Preliminary kinetics analysis show that the diffusion rates in these devices could be improved further. These findings point to the potential design of very broad-band electrochromic systems encompassing the visible through microwave regions. Polyaniline in its insulating states can be considered as a series of linked oligoanilines. These oligoaniline states can either be considered as a model for describing the properties of the polymer, or can be interesting systems themselves in the light of single-molecular electronic devices [12]. Both applied potential and pH can change the electronic states of these systems. The ability of pH to modify the oxidation states in these systems (and induce electronic transport), and the influence of water on these properties can be a model for biological systems too. While a wealth of information on oligoanilines has been generated from experiments, computational modelling of these systems is less reported. Among many computational methods that have been developed for calculation of optical absorption spectra of molecules, Time Dependent Density Functional Theory (TDDFT) is the method with the widest use. TDDFT obtains the excitation energies of a molecule from the linear response of the electronic density to a external perturbing field [13]. Solvent effects, which are known to affect the excitation energies, are included through the SCRF/PCM (Self-consistent Reaction Field/ Polarizable Continuum Model). PCM is a method that treats the solvent molecules as a continuum, and self-consistently evaluates their electronic distribution around the solute. In the fifth chapter, a systematic study of the optical properties of neutral oligoaniline, in three oxidation states, is performed by varying the chain length and linearity of the backbone. The intrinsic accuracy in the excitation energies obtainable by the combined TDDFT/PCM formalism has enabled us to suggest effective oligomer lengths for the optical transitions in Polyaniline; these are 4 rings for emeraldine base, 4–8 rings for leucoemeraldine base and 4 rings for pernigraniline. The sensitivity of the 2.0 eV exciton peak in emeraldine base to the chemical environment is also apparent from this work. The Valence Density of States (VDOS) and vibrational frequencies, that have been obtained in course of these simulations, have been quantitatively analysed and are a useful addition to understanding the optical properties of neutral Polyanilines. A summary of the results of the dopant and water dependence on the electronic and structural properties of protonated oligoanilines was presented in the third chapter; the appendix describes the methodology in detail. It is worthwhile to emphasize that doped Polyaniline is a system where protonation, hydration and extended β-conjugation all occur together synergistically, and a good overall description of this system is necessary. Modelling the doped state of Polyaniline is a bit more difficult, due to spin polarisation. Ideally, conducting Polyaniline should be modelled in the solid state, with neighbouring chains, counterions and water molecules. Water is known to reversibly increase the macroscopic conductivity and ESR linewidth of doped Polyaniline. In the sixth chapter of this thesis, optical spectra of the bipolaron, separated polaron, and the polaron lattice forms of doped Polyaniline, explicitly including the counterions (Cl, Br, AMPSA) are obtained by the TDDFT method. All the polaronic lattice forms show a dominant absorption at 1.0–1.2 eV, with no absorptions in the range 1.4–2.0 eV. The inclusion of water molecules to solvate the counterions is shown to only weakly modify the optical properties in the polaron lattice form. In the case of polarons on a twisted chain, the 1.0 eV peak is shifted to 1.5 eV. For bipolarons, there is an absorption at 1.3–1.5 eV, along with another peak at 1.8 eV. Comparing with experimental spectra we suggest that the 1.5, 2.8 eV set belongs to a polaron lattice form wherein the chains are twisted. However, individually the 1.5 eV peak may equally come from bipolarons or separated polarons. The peak at 1.8 eV may either be ascribed to a bipolaron form (in which case there should be a 1.5 eV peak too), or to an isolated polaron. The isolated polaron may also show a peak at 2 eV and 3.5 eV that is clearly from a residual emeraldine base electronic state. The steady evolution of the (a) 2 eV exciton peak in emeraldine base to a (b) 1.6– 1.8 eV peak (isolated polarons) to a (c) 1.5 eV peak in the bipolaron form to (d) 1.3 eV peak in the separated polaron form to (e) a 1.0–1.2 eV peak in the fully doped metallic polaron lattice form is clear. This steady evolution observed from TDDFT simulations may help in clarifying the experimental assignments, especially in electrochemical studies on Polyaniline. Simulations including the water molecules were performed to study the experimentally observed dramatic changes on hydration in Polyaniline. However hydration of ions is a dynamic process and static geometries may not provide a fully realistic description. Combined ab initio Molecular Dynamics (AIMD) and TDDFT calculations may be necessary to realistically model the transport properties of doped Polyaniline. This chapter tries to lay a foundation for such work. The main results obtained in this thesis are summarized in the conclusion. To conclude, this thesis is on the electronic and optical properties of Polyaniline. An ESR study on AMPSA doped Polyaniline indicated a unique 2D nanoscopic morphology, and this structure was validated by molecular modelling. The detailed analyses on electrochromic devices led us to perform TDDFT simulations of neutral and doped Polyanilines. These simulations have resulted in clear UV-VIS-IR assignments in all forms of Polyaniline.