This thesis describes the fabrication and properties of novel organic/silicon hybrid field-effect transistor gas sensors. Whilst most of the work used the emeraldine base form of the conductive polymer polyaniline, the response of a device incorporating a metal-free phthalocyanine is also reported. Arrays of p-type transistors in which the gate electrodes were replaced by 'charge-flow' capacitors were fabricated using standard semiconductor processing techniques. Each array consisted of four devices in which the width of metallisation removed from the gate electrode (total width 72 µm) varied from 0 µm (i.e. the control device) to 35 µm. Thin films of the gas-sensitive organic materials were deposited by spin-coating, and chemically patterned within the holes in the gate metallisation. A delay, referred to as the 'turn-on' response, was observed in the drain current on application of a gate voltage. This was shown to depend on the temperature, level of humidity and the presence of certain gases. The electrical operating characteristics of the hybrid device with and without the polyaniline were examined. These included capacitance-voltage measurements, the 'turn-on' response at different temperatures and the variation of threshold voltage with temperature. From these results an understanding of the effect of integrating polyaniline within a p-channel transistor structure was obtained. The 35 µm gate-hole sensor incorporating polyaniline was found to be sensitive to NO(_x) and SO(_2) at room temperature at concentrations as low as 1 or 2 ppm. Decreasing the gate-hole area, and therefore the surface area of polyaniline, reduced the sensitivity of the device. The reactions were found to be reversible, although complete recovery required approximately eight hours. A similar sensor incorporating a metal-free phthalocyanine compound was reversibly sensitive to 2 ppm NO(_x) with a more rapid recovery of five hours. There was no observable response to SO(_2) or H(_2)S up to 30 ppm.

<p>As a source of life, water is one of the most precious commodities for all living organisms. Water resources are reported to be declining in numbers or the amount of water present and the existing onses are being polluted as a result of negligent human activities and intense industrialisation. thus, there is an ever increasing demand to monitor the quality of portable and waste water in our surroundings in real time. This study has been directed towards the prepaparation of polyanilines.</p>

Philosophiae Doctor - PhD / As a source of life, water is one of the most precious commodities for all living organisms. Water resources are reported to be declining in numbers or the amount of water present and the existing onses are being polluted as a result of negligent human activities and intense industrialisation. thus, there is an ever increasing demand to monitor the quality of portable and waste water in our surroundings in real time. This study has been directed towards the prepaparation of polyanilines. / South Africa

>Magister Scientiae - MSc / Environmental pollution is always the hottest topic in public conversation and one of the most concerned aspects of human health. The thin film sputtered microelectrode devices have been developed to improve the quality of human health, by offering better monitoring capabilities. This thesis is divided into three parts and the studies were performed on chemical sensor technology currently available and under development using modified methods. In the first part of this thesis: (i) the studies are related to synthesis, characterization and polymerisation of polyaniline (PANI) and polyaniline-co-poly(2,2´-dithiodianline) (PANI-co-PDTDA). Polyaniline (PANI) and the copolymer of aniline with dithiodianiline, an aniline derivative containing S-S-links were of interest in polymer synthesis. Electrochemical synthesis was carried out in 1 M HCl and different concentrations of H2SO4 (1, 2.5, and 5 M) solutions for PANI and PANI-co-PDTDA respectively. The PANI and PANI-co-PDTDA were grown electrochemically on the surface of a glassy carbon electrode (GCE) by repetitive cyclic voltammetric scanning. Cyclic voltammetry (CV) was used to evaluate the differences between the electrochemical characteristics associated with growth of the copolymer and homopolymer, polyaniline (PANI). The surface concentration of PANI was estimated to be 2.64 × 10-1 mol.cm-2 while the film thickness was estimated to be 7.09 × 10-10cm and 1.49 × 10-9cm for scan rate and aquare root scan rate. In contrast, PANI-co-PDTDA concentrations (1, 2, 5 and 5 M H2SO4 solutions) gained a surface concentration (G) falling in the range 6.1 x 10-2 - 7.9 x 102 mol.cm-2 and a film thickness in the range 8.16 x 10 -9- 2.05x10-8cm. The second section of this thesis focused on the development of two sensors, Pt/PANI/HRP and Pt/PANI-co-PDTDA/HRP biosensors. The biosensor described in this chapter focus on the use of horseradish peroxidise (HRP) with hydrogen peroxide as substrate, was constructed with the aim of further investigation of inhibition by heavy metals (Cd2+, Pb2+ and Hg2+). To achieve this, the enzyme HRP as the catalytic bio-element, was immobilised on the surface of a platinum electrode with PANI as a mediator. Immobilisation of HRP in conducting polymer matrices of PANI and PANI-co-PDTDA were achieved by electrochemical polymerisation. The use of amperometric detection allowed for the coupling of the biosensor with a portable potentiostat system (PalmSens). Differential pulse voltammetry (DPV) as technique was used as a detection method for inhibition determination. Selection of suitable pH values for biosensor performance was evaluated and the system showed optimal performance at pH 6.8 and 7.2 for Pt/PANI/HRP and Pt/PANIco- PDTDA/HRP biosensors, respectively. The biosensors developed in this work showed detection limits (LODs) of 0.32 mM and 0.0483 mM for PANI/HRP and PANI-co- PDTDA/HRP, respectively. For the Pt/PANI/HRP biosensor, the apparent Michaelis-Menten constant (Km app) value and maximum current (Imax) were evaluated from Lineweaver-Burk plots at various H2O2 concentrations. The values were found to be 0.6 mM and 1.7 μA for the Pt/PANI/HRP biosensor, while for the Pt/PANI-co-PDTDA/HRP biosensor the results were 0.7 mM and 0.27 μA, respectively. The third section investigated the adsorptive cathodic differential pulse stripping voltammetric (AdDPSV) determination of platinum group metals (PGMs), using an ex situ bismuth coated screen printed carbon electrode (SPCE/Bi) as the working electrode and ammonium buffer solution (pH = 9.2) as the supporting electrolyte. The cathodic stripping differential pulse method was used for investigating the electrochemical behaviour and the quantitative analysis of platinum group metals (Pt, Pd and Rh) at the SPCE/Bi surface in the presence of dimethylgloxime (DMG) as a complexing agent. In order to determine the metals at improved detection limits ensuring repeatability and sensitivity, a complete optimization study of voltammetric parameters was performed. The proposed method was successfully applied to the determination of the real samples (sediments & water) collected in the platinum mining area in the North-West and Limpopo Provinces, South Africa. The results were compared with those obtained by the glassy carbon bismuth film (GC/BiF) voltammetric and ICP-AES spectrometry techniques. Well-shaped voltammograms with clear peak potentials were obtained in the analysis of the real samples, offering excellent perspectives on the use of the constructed modified electrodes. The calibration curves for all PGMs investigated were linear with the limit of detection (LOD) at approximately 0.008, 0.006, and 0.005 μg.L-1 for Pd, Pt and Rh, respectively.

No description available.

No description available.

La conductivité électronique de l'éméraldine sel dépend des conditions de sa synthèse (solvant et dopant utilisés) et de son traitement après synthèse. L'objectif principal de cette thèse est de démontrer et d'interpréter les corrélations entre l'environnement et les propriétés de la forme conductrice de la polyaniline. Dans la partie théorique, nous avons examiné l'influence des différents dopants et solvants sur la structure et les propriétés de la polyaniline. Pour atteindre cet objectif, un large dispositif de méthodes de chimie quantique a été testé et une méthode appropriée a été choisie. Dans la partie expérimentale nous avons utilisé une nouvelle approche pour accéder aux propriétés intrinsèques de la polyaniline i.e. sans utiliser ni solvants ni dopants autres que ceux utilisés lors de la synthèse. Les calculs montrent que la description théorique de la polyaniline dépend fortement du choix de la méthode. La modélisation de l'effet de la polarité du solvant grâce à l'utilisation de la méthode PMC semble être cruciale pour une description fiable de l'interaction polyaniline-dopant. Les résultats obtenus démontrent pour la première fois que les interactions, de la polyaniline avec les dopants dépendent de la nature chimique du solvant et pas du dopant lui-même. De plus, nous avons montré que la stabilité de la forme polaronique (conductrice) augmente avec l'augmentation de la polarité du solvant. Ces conclusions correspondent parfaitement à nos résultats expérimentaux qui montrent le rôle crucial du solvant (et pas des dopants) sur les propriétés de la polyaniline. / The electric conductivity of the emeraldine salt depends on the conditions of its synthesis (solvents and dopants) and post-synthetic treatment. The main objective of the present thesis is to demonstrate and interpret the correlations between the environment and the properties of the conductive form of polyaniline. In order to achieve this goal a new theoretical approach is developed with reference to the experimental data. In the theoretical section, we examine the influence of different dopants and solvents on the structure and properties of polyaniline. To achieve this, a variety of quantum chemistry methods is tested and a proper method is chosen. In the experimental part we use a new method for tuning of the intrinsic polyaniline properties without using solvents or dopants other than those employed in the synthesis. The calculations show that the theoretical description of polyaniline depends strongly on the choice of the method. Modeling the effect of solvent polarity (in this case by the PCM method) seems to be crucial for the reliable description of the interaction polianiline-dopant. The obtained results demonstrate for the first time that interaction of polyaniline with dopants depends on the chemical nature of the solvent and not on the dopant itself. In addition, the stability of the polaronic form (conducting) grows with the increase of solvent polarity. These findings correspond well to our experimental results that show the crucial role of the solvent (and not of the dopants) for the properties of polyaniline.

No description available.

Dans ce travail, les structures et les propriétés de plusieurs nanocomposites à base de Polyaniline sont étudiées avec le double objectif de réaliser un capteur d’ammoniac à très faible seuil de détection et une structure de blindage électromagnétique légère. Les aspects relatifs à la structure de bande, le dopage, le transport électronique et les phénomènes de percolation sont abordés. Ensuite, l’élaboration des composites se fait par le dopage de la PAni par l’acide camphre-sulfonique (CSA), qui permet la protonation de la PAni sous sa forme isolante (émeraldine base), avec un rapport molaire variant de 5% à 50%. Cependant, sous sa forme dopée (sel d’émeraldine), la PAni possède des propriétés mécaniques incompatibles avec les applications envisagées il est donc indispensable de réaliser des mélanges avec des thermoplastiques pour associer les propriétés électriques du polymère intrinsèquement conducteur aux propriétés mécaniques du thermoplastique. La conception du capteur d’ammoniac à été faite en plusieurs étapes: nous avons particulièrement étudié l’influence de la nature de la matrice hôte et l’effet du taux de dopage sur les caractéristiques métrologiques des capteurs. Le choix de la matrice ainsi que la stœchiométrie entre PAni et acide impactent directement le seuil de détection et l’amplitude de la réponse du capteur. Les résultats obtenus dans cette première partie du travail montrent qu’il est possible de détecter des teneurs d’ammoniac de l’ordre de 10 ppb en utilisant des composites à base de PAni dopée CSA avec un rapport molaire de 25%, et dispersée dans une matrice Polyuréthane (Pu). Dans la deuxième partie de ce travail, nous avons développé des matériaux hybrides multicouches, en incluant des nanoparticules magnétiques dans les composites conducteurs à base de PAni. L’optimisation des propriétés électroniques du matériau a permis de concevoir une structure bicouche qui répond aux besoins industriels (efficacité de blindage (SE) > 40 dB) et militaires (SE > 80 dB) de blindage électromagnétique. Les épaisseurs totales qui ont été déterminées sont de 530µm pour SE>40dB et 870µm pour SE>80dB. Les structures réalisées, sont également capables d’absorber une grande partie des ondes incidentes, leurs coefficients d’absorption sont supérieurs à 4dB sur la bande de fréquence [8-18GHz]. / In this work, the structure and the properties of Polyaniline (PAni) based nanocomposites are investigated with the dual objective of conceiving an ammonia sensor with very low detection limit and a light electromagnetic shielding structure.Aspects relating to the band structure, the doping, the electron transport and percolation phenomena are discussed. Then, the preparation of composites was made from the doping of PAni by Camphor Sulfonic Acid (CSA), which allows the protonation of PAni in its insulating form (Emeraldine base). The molar ratio of the protonation ranges from 5% to 50%. However, when the PAni is doped, the mechanical properties are not compatible with the targeted applications. Therefore, it is essential to make blends with thermoplastics to combine the electrical properties of PAni with the mechanical properties of thermoplastic. In case of ammonia sensor, we particularly studied the influence of the nature of the host matrix and the effect of the doping level on the sensor metrological characteristics. The choice of the matrix and the stoichiometry between PAni and acid directly impact the detection threshold and the amplitude of the sensor response. The results obtained demonstrate the possibility to detect concentrations of ammonia of about 10 ppb using composite based on PAni doped CSA, with a molar ratio of 25%, dispersed in Polyurethane (Pu) matrix. In the second part of this work, we have developed a hybrid multilayer material, based on PAni doped CSA and magnetic nanoparticles. The influence of electrical properties of each layer on the material performance was studied. A bilayer structure has been optimized for industrial standards (shielding effectiveness SE>40 dB) and military standards (SE>80 dB) of electromagnetic shielding. The total thicknesses that were retrieved are 530µm for SE>40 dB and 870µm for SE>80 dB. The realized structures are also able to absorb much of the incident waves, their absorption coefficients are greater than 4 dB over the frequency band [8-18GHz].

Regensburg, Univ., Diss., 2003.