Electrically conductive smart textiles are a very interesting area that could be important for the development of smart textiles. Today, conductive yarns and threads are often produced from coveted metals such as silver, copper and gold. These metals require large resources to be extracted and processed into yarns and threads and have a major impact on humans and the environment. One way to reduce the consumption of metals and save resources is to coat yarns of textile materials with electrically conductive polymers. In this study, we will investigate coating yarns with the conductive polymer blend PEDOT-PSS. PEDOT-PSS is extracted from oil, which is a non-renewable raw material, but coating with this polymer dispersion has many other advantages over metals and its production chain. Like coating yarn through a chemical bath produces very little waste, the yarn has a smaller mass, the yarn becomes more flexible, and it is easy to scale up production. However, previous studies have shown that there are some difficulties when it comes to coating yarns with PEDOT-PSS. The coating becomes fragile and brittle and to some extent affects the yarn that is coated in terms of mechanical properties. In this study, its investigated how the yarn is affected by various parameters in the production line, such as drying temperature, the viscosity of the PEDOT-PSS dispersion and the speed of the thread traveling through the production line, to find optimal production parameters that provide a balance between conductive and mechanical properties. We have produced a number of samples, all with different variations of parameters, and investigated how its conductive and mechanical properties are affected to see if there is a pattern and connection between parameters and conductive and mechanical properties on the yarn. The results show that yarn samples made with high viscosity of the PEDOT-PSS dispersion are among the lower range of resistance (with some exceptions), with average values of about 2990 O up to 10300 O, while lower viscosity shows uneven results with average values of about 92,000 O and all the way up to about 6,500,000 O. Most samples with lower measured O values are made with a high drying temperature, but no clear connection could be detected between temperature and end result, nor did the different speeds show any clear connection to the result. For the mechanical properties, it turns out that there is a relationship between result and viscosity as well as result and drying temperature. Samples made with low viscosity and low drying temperature perform best in the mechanical tests, 59.7% to 52.9% elongation and 25 cN / tex to 21 cN / tex. While speeds in this category could not show any connection between the results either. Overall, the results can be summarized as the results of tests show that there are some correlations between the parameters and the properties of the yarn samples and that the viscosity of the PEDOT-PSS dispersion and drying temperature are the most influential parameters. For conductive properties, viscosity has the greatest effect and for mechanical properties, viscosity and temperature have the greatest effect. For conductive properties, high viscosity is good, and for mechanical properties, low temperature and low viscosity are best. The sample with the best combination of test results was tested in a knitting machine but the variant chosen for knitting did not have good enough mechanical properties for the knitting machine used and broke when exposed to the stress from the knitting process. Therefore, the knitting test was not successful, but it was possible to sift out what parameter of the production line that had the greatest impact on the coated yarn properties.

Les actionneurs à base de polymères électroactifs ioniques constituent une alternative prometteuse par rapport aux actionneurs conventionnels, en particulier lorsqu’une réponse comparable à celle d’un muscle naturel est recherché. Parmi eux, les actionneurs à base de polymères conducteurs constituent une voie prometteuse pour des applications biomédicale où la biocompatibilité, la compacité et un positionnement précis sont requis. Néanmoins, l’essor de dispositifs fonctionnels est fortement ralenti en raison de la faible efficacité d’actionnement et de la rapide dégradation des performances de ce type d’actionneurs. L’absence de rétroaction sur la force ou sur la position est également un autre aspect limitant le développement de cette approche. L’objectif de cette thèse est de proposer une technique de fabrication à grande échelle pour l’élaboration d’actionneurs à base de polymères électroactifs ioniques et permettant également l’intégration de capteurs pour un contrôle rétroactif. L’impression par jet d’encre est une technologie clé pour le dépôt de polymères et une des plus alternatives les plus prometteuses pour la production d’actionneurs à base de polymères conducteurs. Cependant, la fabrication d’actionneurs par technique jet d’encre n’est pas encore totalement maîtrisée à cause des propriétés rhéologiques des solutions de polymères conducteurs qui rendent difficile le contrôle de l’éjection de gouttes mais également en raison de la nature complexe des interactions entre la solution et l’échantillon qui peut conduire à une faible adhésion et un mauvais contrôle de l’infiltration de l’encre. Pour optimiser cette méthode de fabrication, des membranes hybrides contenant des ions ont été développées. Le greffage d’un monomère hydrophile par plasma argon avec un dépôt contrôlé en profondeur a été utilisé pour obtenir des membranes en polyfluorure de vinylidène (PVDF) avec des surfaces hydrophiles tout en conservant une zone centrale hydrophobe. Ces membranes hybrides ont permis d’obtenir, par dépôt de gouttes, des actionneurs de morphologies très variées à base de polymères conducteurs. En outre, la durée de vie d’actionneurs obtenus avec une solution conductrice de poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) a été sensiblement augmentée avec des déformations de plus de 0.6% sans qu’aucun signe de délamination ne soit perceptible. Enfin, la nature complexe des mécanismes physico-chimiques à l’origine des interactions entre le film polymère et la membrane poreuse a été mieux appréhendée durant ce travail. Les conditions nécessaires pour assurer une forte adhésion et les effets conduisant à un mauvais contrôle de l’infiltration ont été partiellement identifiés. Ces résultats ont permis de définir les paramètres clés concernant la préparation de la membrane et la composition de la solution polymère. En associant l’ensemble de ces résultats avec les exigences liées à l’utilisation de l’impression de solutions par jet d’encre, nous avons réalisé, en utilisant cette technique de dépôt, les premiers actionneurs ioniques à base de PEDOT:PSS. / Onic electroactive polymer based artificial muscles are promising alternative to traditional actuators, especially where compliant muscle-like response is desirable. Among them, conducting polymer actuators (CPAs) are most promising for biomedical applications, where biocompatibility, compactness and accurate positioning is essential. Nevertheless, development of applicable devices is hold down by their low efficiency and fast performance deterioration. The absence of a tactile, force or position feed-back is another feature limiting the development of functional devices. The goal of this thesis is to develop a fabrication technique for conducting polymer based actuators that could be up-scalable and enable facile integration of sensory feedback. Inkjet printing is key technology in the field of defined polymer deposition as well as in fabrication of strain sensors. It is also one of the most promising alternatives to prevalent fabrication of conducting polymer actuators. Nevertheless, inkjet printed actuators were not yet realized due to rheological properties of conducting polymer solutions that challenge jetting and the complex solution - membrane interactions, that lead to poor adhesion or uncontrolled infiltration. In order to enable this fabrication method, hybrid ion-storing membranes were developed. Argon plasma induced grafting-to of hydrophilic macromonomer with limited-indepth deposition was used to obtain polyvinylidene fluoride (PVDF) membranes with hydrophilic upper surfaces and hydrophobic centre. Functionalized PVDF membranes were shown to withhold good adhesion to the conducting polymer films and preserve electrically insulating layer in between them. Hybrid membranes were demonstrated to be advantageous in fabrication of CPAs by drop casting and enable production of actuators with various morphologies. Furthermore, fabricated poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based actuators demonstrated long lifetime with no signs of delamination as well as large strain of more than 0.6%. In addition, the complex nature of the physico-chemical mechanisms of the interactions between the polymer film and the porous membrane was better understood during this work. The conditions necessary in order to ensure strong adhesion as well as circumstances leading to uncontrolled infiltration were partially identified. These were used to set up limits to membrane preparation and polymer solution composition. Combining obtained knowledge with known requirements for inkjet printable solutions lead to the realization of the first inkjet printed PEDOT:PSS based ionic actuators.

Poly(3,4-ethylenedioxythiophene), PEDOT, belongs to the group of conducting polymers and is characterized by its high stability, a moderate band gap and its optical transparency in the conductive state. A large disadvantage of conducting polymers, and also PEDOT, is their poor solubility. One way to achieve processible materials is the synthesis of colloidal particles. Thus, this work focuses on the development of conductive particles by preparing composite structures. Polymeric colloids like latex particles and microgels were used as templates for the oxidative polymerization of EDOT. Depending on template structure completely different composite morphologies with variable properties were obtained. It was found that modification with PEDOT did not only cause conductive particles for application as humidity sensor materials, but also candidates for further functionalization with gold nanoparticles (Au-NPs). Due to a multi-stage synthesis route it was possible to achieve polystyrene(core)-PEDOT(shell)-particles decored with Au-NPs. Microgels acting as “micro reactors” for the incorporation of PEDOT and Au-NPs were also used for preparing multifunctional composites for catalytic applications. / Poly(3,4-ethylendioxythiophen), PEDOT, gehört zur Gruppe der leitfähigen Polymere und zeichnet sich durch seine hohe Stabilität, eine moderate Bandlücke und seine optische Transparenz im dotierten Zustand aus. Ein Nachteil leitfähiger Polymere, wie auch von PEDOT, ist deren schlechte Löslichkeit. Die Synthese kolloidaler Partikel bietet jedoch eine Möglichkeit dieses Problem zu umgehen. In diesem Zusammenhang richtete sich der Fokus dieser Arbeit auf die Darstellung leitfähiger Partikel in Form von Kompositstrukturen. Polymerkolloide, wie Latex- und Mikrogelpartikel, sind als Template eingesetzt worden, in deren Gegenwart PEDOT durch eine oxidative Polymerisation synthetisiert wurde. In Abhängigkeit von der Struktur des Templats sind unterschiedliche Kompositmorphologien mit steuerbaren Eigenschaften erhalten worden. Auf diese Weise wurden neben Materialien für die Feuchtigkeitssensorik leitfähige Kompositpartikel hergestellt, die zusätzlich mit Gold-Nanopartikeln (Au-NP) funktionalisiert werden konnten. Durch ein mehrstufiges Syntheseverfahren sind somit Polystyrol(Kern)-PEDOT(Schale)-Partikel mit Au-NP-funktionalisierter Oberfläche synthetisiert worden. Mikrogelpartikel, die als „Mikroreaktoren“ für die Inkorporation von PEDOT- und Au-NP dienten, wurden ebenfalls eingesetzt, um multifunktionale Komposite mit katalytischen Eigenschaften herzustellen.

Avec la demande sans cesse renouvelée de matériaux éco-compatibles pour l’électronique de demain, les polymères conducteurs se sont imposés comme une alternative intéressante aux matériaux déjà existants. Ils doivent leur popularité principalement à leurs propriétés électriques, optoélectroniques, thermo-chromiques, luminescentes et mécaniques, couplées à leur bonne processabilité et leur faible impact environnemental. Parmi eux, le poly(3,4-ethylenedioxythiophene) (PEDOT) est certainement le plus connu est le plus utilisé. De nombreuses études se sont focalisées sur l’optimisation de sa conductivité électrique et des progrès remarquables ont été réalisés. Cependant, la compréhension fine de la relation structure/propriétés de ce matériau reste à élucider. C’est ainsi que dans le cadre de cette thèse nous avons décidé de plusieurs objectifs qui sont (1) la synthèse de PEDOT hautement conducteurs à structure contrôlée et optimisée, (2) l’étude des propriétés électriques, structurales et de transport électroniques dans ces PEDOT, (3) l’étude de leurs propriétés thermoélectriques et (4) l’étude de leur stabilité sous différentes conditions afin de valider leurs potentielles applications. Ainsi, après une revue de la littérature sur le PEDOT, nous étudions l’amélioration de la conductivité électrique du PEDOT:OTf et du PEDOT:Sulf, qui atteint dorénavant des valeurs à hauteur de 5400 S cm-1. Différentes techniques de caractérisation nous ont permis de mener une étude exhaustive de leurs propriétés électriques et structurales ainsi que des mécanismes de transport électronique qui en découlent. Nous nous sommes ensuite intéressés à deux de leurs propriétés thermoélectriques, l’effet Joule et l’effet Seebeck, le premier pour des applications en chauffage et le deuxième pour la récupération d’énergie. L’utilisation pour la première fois du PEDOT comme film chauffant flexible transparent est d’ailleurs présentée. On démontre par exemple que PEDOT:Sulf présente une résistance carrée de 57 Ω sq-1 pour 87.8 % de transparence et qu’une température de 138 °C peut être atteinte lorsqu’on applique 12 V. Cette thèse se conclut sur l’étude de la stabilité de nos matériaux de PEDOT sous différentes atmosphères ainsi que l’étude des mécanismes de dégradation. / With the rising demand of flexible, low cost and environmentally friendly materials for future technologies, organic materials are becoming an interesting alternative to already existing inorganic ones. Organic photovoltaics, organic light emitting diodes, organic field effect transistors, organic thermoelectricity, organic transparent electrodes are all evidences of how organic materials are sought for tomorrow. Materials which can fulfill the requirements specifications of future technologies are conducting polymers, which owe their popularity to their outstanding electrical, optoelectronic, thermochromic, lighting and mechanical properties. Moreover, they exhibit good processability even on flexible substrates and low environmental impact. Poly(3,4-ethylenedioxythiophene) (PEDOT) is certainly the most known and most used conducting polymer because it is commercially available and shows great potential for organic electronics. Studies dedicated to PEDOT films have led to high conductivity enhancements. However, an exhaustive understanding of the mechanisms governing such enhancement is still lacking, hindered by the semi-crystalline nature of the material itself. In such a context, this thesis has four objectives which are (1) the synthesis of PEDOT materials with an optimized and controlled structure to enhance the electrical properties, (2) the thorough characterization of the as-synthesized PEDOT in order to understand the charge transport mechanisms, (3) the study of their thermoelectric properties and (4) the study of their stability under different environments and stresses. Thus, after a literature review on PEDOT materials, we present the enhancement of the electrical conductivity of PEDOT:OTf and PEDOT:Sulf up to 5400 S cm-1 via a structure and dopant engineering, and then thoroughly study their electrical and electronic transport properties. Subsequently, two thermoelectric properties of PEDOT are investigated, namely its resistive Joule heating ability and its Seebeck effect, for both heating and energy harvesting applications. A novel application of PEDOT as flexible transparent heater is demonstrated in the first case. PEDOT:Sulf for example exhibited a sheet resistance of 57 Ω sq-1 at 87.8 % transmittance and reached a steady state temperature of 138 °C under 12 V bias. Finally, this thesis is concluded with the ageing and stability of our PEDOT based materials under different environmental stresses. While PEDOT is stable under mild conditions, heavy degradations can occur under harsh conditions. The degradation mechanisms are then investigated in this last part.

Solid state lighting is a new environmentally friendly light source. So far, light emitting diodes (LEDs) and organic LEDs (OLEDs) have been presented as candidates with potentially high efficiency. Recent advances of OLEDs in device architecture, light-out coupling, and materials have ensured high efficiency, exceeding that of incandescent light bulbs. In contrast to conventional point source LEDs, OLEDs distribute light throughout the surface area and are not restricted by their size. Additionally, OLEDs are expected to reach sufficient stability in the near future. The remaining challenge for OLEDs is their cost. New OLED technologies provide cost effective manufacturing methods which could be presented for transparent electrode materials because indium tin oxide (ITO), a widely used material as a transparent electrode for OLEDs, is less than optimal due to its high element price. In this work, alternative transparent electrodes for OLEDs as a replacement of ITO were studied. First, Al doped ZnO (ZnO:Al) which is composed of abundant materials was investigated with DC magnetron sputtering under a wide range of experimental conditions. The optimised ZnO:Al received comparable performance with conventional ITO films, low sheet resistance of 22.8 Ω/sq as well as a high transparency of 93.1 % (average value in the visible range). Various type of p-i-n OLEDs were employed on the structured ZnO:Al using photolithography. Green OLEDs with double emission layers have been archived stable efficiencies even at higher luminance. Also, OLEDs using two fluorescent colour system on ZnO:Al anode showed a purely white emission. It has been found that the OLEDs on ZnO:Al anode has comparable or better device efficiencies and operational lifetime compared to OLEDs on conventional ITO anode. As another alternative electrode, the conductive polymer Baytron®PH510 (PEDOT:PSS) was investigated. Due to a relatively high sheet resistance of PEDOT:PSS, metal grid was designed for large size OLEDs. White OLEDs on PEDOT anode with a size of 5 × 5 cm2 have achieved more than 10 lm/W of power efficiency using a scattering foil. Furthermore, up-scaled devices on 10 × 10 cm2 were also demonstrated. These results showed ZnO:Al and PEDOT are suitable for OLEDs as anode and have high potential as alternative transparent electrode materials.

Poly(3,4-ethylendioxythiophen) (PEDOT) ist ein Kunststoff der zur Gruppe der intrinsisch leitfähigen Polymere (ILP) zählt. Aufgrund seiner chemischen und thermischen Stabilität findet er Verwendung in antistatischen Verkleidungen und als Elektrodenmaterial. PEDOT (und andere ILP) zeigen aufgrund ihrer Schaltbarkeit zwischen (reduzierten, ) neutralen und oxidierten Zuständen unterschiedliche Eigenschaften wie Leitfähigkeit, Farbe oder Viskoelastizität. Im Rahmen dieser Arbeit wurden die elektrochemischen und viskoelastischen Eigenschaften von PEDOT-Filmen untersucht. Dabei wurde die Quarzmikrowaage (QCM) in Verbindung mit potentiostatischen (Potentialsprung, PS) und potentiodynamischen (Cyclovoltammetrie, CV) elektrochemischen Methoden verwendet, so dass in situ elektrochemische und mechanische Eigenschaften der Filme zugänglich waren. Zur Bestimmung der viskoelastischen Eigenschaften wurde ein Auswertealgorithmus entwickelt, welcher auf ein mathematisches Modell zur Bestimmung des Schermoduls nach Efimov zurückgreift. Während der Herstellung wurden Parameter wie Lösungsmittel, Leitsalz, Vorpolarisations- und Abscheidungspotential variiert und die erhaltenen Filme bezüglich Schermodul und Morphologie charakterisiert. Es konnte gezeigt werden, dass die Elektrolytzusammensetzung einen entscheidenden Einfluss auf die viskoelastischen Eigenschaften der Filme besitzt, welche mit der Morphologie der Filme korrelieren. Des Weiteren wurden die Änderungen der viskoelastischen Eigenschaften dieser Filme untersucht, welche während dem elektronischen Schalten zwischen neutralem und oxidiertem Zustand aufgrund des Ionenaustausches erfolgen. CV- und PS-Experimente zeigten, dass die viskoelastischen Eigenschaften durch Konzentration und pH-Wert des Elektrolyten beeinflusst werden und in unterschiedlicher Weise auf die Potentialänderungen reagieren. Durch den Einbau von Magnetit-Partikeln in die Schichten konnten Hybridfilme erhalten werden, deren Eigenschaften durch das Anlegen eines äußeren Magnetfeldes beeinflusst werden können. Solche Filme zeigten in einem äußeren Magnetfeld (0,7T) höhere Schermodule und einen stark unterdrückten Ionenaustausch.

Différents systèmes polyoxométallates@M-colorants ont été réalisés dans cette thèse pour électrochimique dégagement d'hydrogène catalytique et génération photocourant.• Des films hybrides, basés sur des interactions électrostatiques entre une porphyrine tetracationique et des nanoparticules stabilisées par des POMs du type POM@Pt sur ITO, ont été formés par la méthode dite couche par couche et ont été utilisés pour la génération de H2 ou de photocourant. • Pour améliorer le transfert de charge entre les nanoparticules POM@M et le substrat, la réduction de l'oxyde de graphène a été réalisée pour former des systèmes hybrides rGO/POM@Pt. Le dégagement d'hydrogène a été mesuré.• Les copolymères polycationiques bis-porphyrine ont également été obtenus par électropolymérisation avec des espaceurs bis-pyridinium. Par réaction de métathèse, l’incorporation avec divers POM de type Keggin ou des nanoparticules du type POM@Ag ont ensuite été realise. Leurs performances photovoltaïques ont ensuite été étudiées.• Enfin des films hybrides PEDOT dopés avec des nanoparticules du type POM@M ont également été fabriqués. Les performances photovoltaïques ont été examinés montrant une forte amélioration sous illumination dans le domaine du visible. L’ensemble de ces matériaux hybrides ont montré des propriétés intéressantes pour des applications photovoltaïques et la conversion d'énergie. / Polyoxometalates@M NPs-dyes molecular hybrid systems were realized in this thesis for electrochemical catalytic hydrogen evolution and photocurrent generation. • First, hybrid films, based on electrostatic interactions between the tetracationic porphyrin and POMs@Pt NPs composites on ITO slides, were formed by the so called Layer-by-Layer method for HER and photocurrent generation.• To improve the charge transfer between POMs@M NPs and the substrate, reduced graphene oxide was introduced to form rGO/POMs@Pt NPs hybrid systems. Hydrogen evolution was measured after dropping this composites onto the surface of glassy carbon electrodes.• Polycationic bis-porphyrin copolymers have been also obtained by an electropolymerization leading to the formation of new bis-porphyrin copolymers with pyridinium as spacers. Incorporation with various Keggin type POMs or POMs@Ag was then achieved, their photovoltaic performances were also studied.• POMs@M NPs doped PEDOT hybrids films have been also fabricated. The photovoltaic performances has been examined showing particularly strong enhancement under visible light. In conclusion, these polyoxometalates based hybrids materials have shown interesting properties for photovoltaic application and energy conversion.

The study of novel properties of materials in nanometer length scales has been an extensive area of research in the recent past. The field of nanosciece and nanotechnology deals with such studies and has gained tremendous importance because of the potential applications of these nanosystems in devices. Many of the bulk properties tend to change as a function of size, be it particle size in case of nanoparticles, or thickness in case of very thin films. Not only is it important to study these changes from the point of view of applications, but also the interesting physics behind such changes prompts further research and exploration in this area. In this thesis we try to see how changes in the length scales affect the properties of nanoparticles and how change in thickness affects the properties of thin films, along with making an effort towards measurements of conductivity in the nanoscale using the technique of electron magnetic resonance (EMR) signal shape analysis. Electron magnetic resonance is a general term used to combine both electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR). This thesis deals with mainly two kinds of systems viz., nanoparticles of doped rare earth manganites and thin films of the conducting polymer, vapor phase polymerized polyethylendioxythiophene (VPP PEDOT). The general formula for doped manganites is A1-xBxMnO3 where A is a rare earth trivalent cation like La3+, Pr3+, Nd3+..., and B is an alkaline earth divalent cation like Sr2+, Ca2+, Ba2+... These together with Mn and O form the distorted perovskite structure to which manganites belong. The phase diagram of doped manganites involves many interesting phases like ferromagnetic metallic, antiferromagnetic insulating and charge ordered insulating phases. The magnetic properties of the manganites are governed by exchange interactions between the Mn ion spins. These interactions are relatively large between two Mn spins separated by an oxygen atom and are controlled by the overlap between the Mn d-orbitals and the O p-orbitals. The changing Mn-O-Mn bond lengths and bond angles as a function of the radius of the A and B cations [1, 2], and the different magnetic interactions among the Mn3+ and Mn4+ ions together are responsible for the different phases that we see in manganites as a function of temperature and magnetic field. Manganites have potential applications in the field of spintronics because of their colossal magnetoresistance (CMR) [3] and half-metallic [4] properties. Studies on nanoscale manganites have shown that as size reduces, their electrical and magnetic properties change significantly[5]. By changing the morphology and grain size, the properties of CMR manganites can be tuned [6-9]. Phase separation seems to disappear in nanoparticles compared to bulk [10]. In the charge ordered manganites, size reduction is known to bring about suppression of charge order [11], emergence of ferromagnetism [12, 13] and even metallicity in some nanostructures [12]. The conducting polymer under study viz., VPP PEDOT is in a semiconducting phase at room temperature and becomes more insulating as temperature reduces. It is a technologically important polymer which has cathodically coloring property, can be used as a highly conducting electrode in organic solar cells and organic LEDs [14-16]. In the following we give a summary of the results reported in the thesis chapter by chapter. Chapter 1: This chapter of the thesis consists of an introduction to the physics of manganites and the technique of EMR. This includes a detailed account of previous EMR studies done on manganites, in particular nano manganites. There is a section about different line shapes observed in EMR of manganites, their origin and how to fit them to an appropriate lineshape function [17]. There is an introduction to the transport properties of conducting polymers, including how magnetic fields can affect the transport and the mechanism behind variable range hopping transport which is the dominant kind of transport in such polymeric systems. There is also a description of the different experimental methods and instruments used to study the systems in the thesis and their working principles. They are: EPR spectrometer, SQUID magnetometer, Janis cryostat with superconducting magnet, atomic force microscope (AFM) and transmission electron microscope (TEM). Chapter 2: This chapter deals with the method of contactless conductivity of nanoparticles using EMR lineshape analysis. It is difficult to measure the conductivity of individual nanoparticles by putting contacts. Other methods tend to include the contribution of grain boundaries which mask the grain characteristics [5]. We have introduced a new contactless method to measure the conductivity of nanoparticles in a contactless manner [18]. Metallic nanoparticles in which the skin depth is less than the size of the particles, exhibit an asymmetric EMR signal called the Dysonian [19]. Dysonian lineshape is an asymmetric lineshape with the so-called A/B ratio >1, where, A is the amplitude of the low field half of the derivative and B is the amplitude of the high field half. In a ferromagnetic conducting sample, the lineshape has contributions from the Dysonian part and also a part which arises due to magnetocrystalline anisotropy [20]. We have developed a method of deconvoluting the signals from conducting nanoparticles to take out the Dysonian part from them and measure the A/B ratio as a function of temperature. The A/B ratio thus determined can then be used to find out the ratio of the sample size to the skin depth using the work by Kodera [21]. The skin depth can be used to determine the conductivity by using the relationship  = (1/)1/2, where,  is the measuring frequency,  is the conductivity and  is the permeability. This technique has been used to determine the conductivity as a function of temperature (from 60 K to 300 K) of La0.67Sr0.33MnO3 (LSMO) nanoparticles of average size 17 nm. The method has been cross-checked by measuring the conductivity of bulk LSMO particles at 300 K by EMR lineshape analysis method and by standard four-probe method, which give conductivity values close to each other within experimental error. Chapter 3: In this chapter, we report a novel phenomenon of disappearance of electron-hole asymmetry in nanoparticles of charge ordered Pr1-xCaxMnO3 (PCMO). In bulk PCMO there is asymmetry in electric and magnetic properties seen on either side of x = 0.5. In the samples with x = 0.36 (hole doped: called PCMH) and x = 0.64 (electron doped: called PCME), the bulk sample has opposite g-shifts as observed in EPR signals [22]. PCME sample shows g-value less than and PCMH sample shows g-value greater than the free electron g-value at room temperature. This is explained using the opposite sign of the spin-orbit coupling constant for the two different kinds of charge carriers. But when the size of PCMH and PCME is reduced to nanoscale (average size ~ 20 nm), the g-shift was seen on the same side i.e., positive and almost equal g-shift in both cases. This points towards a disappearance of electron-hole asymmetry at nanoscale. This positive g-shift is analyzed in the two cases in the light of disappearance of charge ordering and emergence of ferromagnetism in these systems, since emergence of ferromagnetic hysteresis is noticed at low temperatures in both nano PCMH and nano PCME. In nano PCMH, charge ordering completely disappears and in nano PCME it weakens. Exchange bias is seen in both the systems, suggestive of core-shell structure [23] in the nanoparticles. Other competing factors include spin-other orbit interactions and size reduction induced metallicity [12] which can average out the anisotropies in the system, causing the asymmetry to disappear. Chapter 4: This chapter deals with thickness induced change in transport mechanism in VPP PEDOT thin films. Two samples were studied with average thickness of 120 nm (VP-1) and 150 nm (VP-2). The average room temperature conductivity of VP-1 was found to be 126 Scm-1 and VP-2 was 424 Scm-1. The transport mechanism in VP-1 is seen to be 2-dimensional variable range hopping (VRH) [24]. However, as the thickness increases by 30 nm, the transport mechanism in VP-2 is found to be 3-dimensional VRH. The low temperature magnetotransport is analyzed in the two systems and it shows that there is wavefunction shrinkage in both the systems at 1.3 K [24]. The DC transport results are cross checked with AC transport data at 5 different temperatures in the frequency range of 40 Hz to 110 MHz. The data can be analyzed by using the extended pair approximation model [25]. The AC transport shows the presence of a critical frequency 0 which marks the transition from the frequency independent to a frequency dependent region. The value of 0 decreasing with decreasing temperature suggests that the system is becoming more insulating and it supports the DC transport model of VRH. The morphological studies were done using AFM which revealed higher grain size for VP-2, confirming the direct correlation of the average grain size with the conductivity of the sample. Chapter 5: summarizes the main conclusions of the thesis, also pointing out some future directions for research in the field.

Poly(3,4-ethylendioxythiophen) (PEDOT) ist ein Kunststoff der zur Gruppe der intrinsisch leitfähigen Polymere (ILP) zählt. Aufgrund seiner chemischen und thermischen Stabilität findet er Verwendung in antistatischen Verkleidungen und als Elektrodenmaterial. PEDOT (und andere ILP) zeigen aufgrund ihrer Schaltbarkeit zwischen (reduzierten, ) neutralen und oxidierten Zuständen unterschiedliche Eigenschaften wie Leitfähigkeit, Farbe oder Viskoelastizität. Im Rahmen dieser Arbeit wurden die elektrochemischen und viskoelastischen Eigenschaften von PEDOT-Filmen untersucht. Dabei wurde die Quarzmikrowaage (QCM) in Verbindung mit potentiostatischen (Potentialsprung, PS) und potentiodynamischen (Cyclovoltammetrie, CV) elektrochemischen Methoden verwendet, so dass in situ elektrochemische und mechanische Eigenschaften der Filme zugänglich waren. Zur Bestimmung der viskoelastischen Eigenschaften wurde ein Auswertealgorithmus entwickelt, welcher auf ein mathematisches Modell zur Bestimmung des Schermoduls nach Efimov zurückgreift. Während der Herstellung wurden Parameter wie Lösungsmittel, Leitsalz, Vorpolarisations- und Abscheidungspotential variiert und die erhaltenen Filme bezüglich Schermodul und Morphologie charakterisiert. Es konnte gezeigt werden, dass die Elektrolytzusammensetzung einen entscheidenden Einfluss auf die viskoelastischen Eigenschaften der Filme besitzt, welche mit der Morphologie der Filme korrelieren. Des Weiteren wurden die Änderungen der viskoelastischen Eigenschaften dieser Filme untersucht, welche während dem elektronischen Schalten zwischen neutralem und oxidiertem Zustand aufgrund des Ionenaustausches erfolgen. CV- und PS-Experimente zeigten, dass die viskoelastischen Eigenschaften durch Konzentration und pH-Wert des Elektrolyten beeinflusst werden und in unterschiedlicher Weise auf die Potentialänderungen reagieren. Durch den Einbau von Magnetit-Partikeln in die Schichten konnten Hybridfilme erhalten werden, deren Eigenschaften durch das Anlegen eines äußeren Magnetfeldes beeinflusst werden können. Solche Filme zeigten in einem äußeren Magnetfeld (0,7T) höhere Schermodule und einen stark unterdrückten Ionenaustausch.

Poly(3,4-ethylenedioxythiophene), PEDOT, belongs to the group of conducting polymers and is characterized by its high stability, a moderate band gap and its optical transparency in the conductive state. A large disadvantage of conducting polymers, and also PEDOT, is their poor solubility. One way to achieve processible materials is the synthesis of colloidal particles. Thus, this work focuses on the development of conductive particles by preparing composite structures. Polymeric colloids like latex particles and microgels were used as templates for the oxidative polymerization of EDOT. Depending on template structure completely different composite morphologies with variable properties were obtained. It was found that modification with PEDOT did not only cause conductive particles for application as humidity sensor materials, but also candidates for further functionalization with gold nanoparticles (Au-NPs). Due to a multi-stage synthesis route it was possible to achieve polystyrene(core)-PEDOT(shell)-particles decored with Au-NPs. Microgels acting as “micro reactors” for the incorporation of PEDOT and Au-NPs were also used for preparing multifunctional composites for catalytic applications. / Poly(3,4-ethylendioxythiophen), PEDOT, gehört zur Gruppe der leitfähigen Polymere und zeichnet sich durch seine hohe Stabilität, eine moderate Bandlücke und seine optische Transparenz im dotierten Zustand aus. Ein Nachteil leitfähiger Polymere, wie auch von PEDOT, ist deren schlechte Löslichkeit. Die Synthese kolloidaler Partikel bietet jedoch eine Möglichkeit dieses Problem zu umgehen. In diesem Zusammenhang richtete sich der Fokus dieser Arbeit auf die Darstellung leitfähiger Partikel in Form von Kompositstrukturen. Polymerkolloide, wie Latex- und Mikrogelpartikel, sind als Template eingesetzt worden, in deren Gegenwart PEDOT durch eine oxidative Polymerisation synthetisiert wurde. In Abhängigkeit von der Struktur des Templats sind unterschiedliche Kompositmorphologien mit steuerbaren Eigenschaften erhalten worden. Auf diese Weise wurden neben Materialien für die Feuchtigkeitssensorik leitfähige Kompositpartikel hergestellt, die zusätzlich mit Gold-Nanopartikeln (Au-NP) funktionalisiert werden konnten. Durch ein mehrstufiges Syntheseverfahren sind somit Polystyrol(Kern)-PEDOT(Schale)-Partikel mit Au-NP-funktionalisierter Oberfläche synthetisiert worden. Mikrogelpartikel, die als „Mikroreaktoren“ für die Inkorporation von PEDOT- und Au-NP dienten, wurden ebenfalls eingesetzt, um multifunktionale Komposite mit katalytischen Eigenschaften herzustellen.