Morphological architecturing is one of the smart and efficient ways to maximize the number of excitons harvested from the known photoactive materials and existing fabrication technologies. Surfaces and interfaces play a vital role in absorbing light and therefore when patterned regularly, aid in the improvement of light absorption. This thesis deals with the study of light management by morphologically architecturing the organic electroactive materials. Here, morphological architecturing is carried out using electrospinning technique by optimizing various parameters. In the first part, organic photovoltaic system is tailored by morphologically modifying the conjugated polymer active layer and analyzing the enhancement in light collection and hence performance of photovoltaic devices. In the second part, the prospects of using free standing buffer layer instead of thin film buffer layer in a solar cell is evaluated. Furthermore, the study on morphological engineering of conjugated small molecule is carried out, by varying the solvents and derivatives, in order to control morphologies by understanding the underlying mechanism. Overall this thesis attempts to understand the fundamentals in morphological architecturing, by physical architecturing of the small molecules in a device for light management applications as well as demonstrating improvement in light absorption in existing organic photovoltaic systems. In the introduction chapter, a brief description of organic photovoltaics is given followed by highlighting the importance of processing methods in light management and in organic photovoltaics. The significance of structured architecture in improving the device characteristics is presented. The issues and challenges in existing architecturing techniques available in literature are discussed. Electrospinning as a tool for morphological modification for organic photovoltaics is demonstrated. This is followed by an outline of the thesis. In Chapter 2, brief description of procedures carried out for fabrication, characterization and optimization of electrospinning process parameters are discussed. The description of fabrication procedures including electrospinning, spincoating and thermal evaporation are given. Characterization techniques used in this thesis for surface and feature analysis, structural, compositional, optical and opto-electrical analyses are described. Optimization of electrospinning process parameters in obtaining various morphologies are evaluated. In Chapter 3, enhancement of device characteristics of poly (3-hexylthiophene): phenyl C61-butyric acid methyl ester (P3HT: PCBM) by changing active layer film morphology into network structure is elucidated. Network structure is provided by electrospraying assisted hierarchical assembly of short fibrils. Effect of electrospraying parameters such as solvent, polymer blend concentration, applied voltage, tip to collector distance, flow rate and deposition time are analyzed. Solvent and applied voltage are observed to be the major parameters governing the formation of network structure. The optimized conditions are used to investigate the optical and structural properties. Percent reflectance studies showed improvement in light absorption due to increase in surface area. Structural characterization studies indicate an increase in orientation of crystallites and crystallinity as compared to spincoated samples. The optimized conditions along with additional spincoated layer of P3HT:PCBM are used to fabricate bulk heterojunction device. Device characteristics exhibited an increase in short circuit current and thus increase in efficiency from 2.18% to 3.66%. There is a enhancement of 37.5% going from maximum external quantum efficiency of 40%-55% for electrosprayed and spincoated devices. It is anticipated that network morphology could be the next possible structure to be explored in organic photovoltaic materials. In Chapter 4, photonic structure is analyzed and compared. A photonics device requires uniform periodic structural arrangement. Various techniques are used to fabricate these types of structures, employing several steps of fabrication. This work proposes single step hierarchical array of equal submicron size porous structure fabricated by tuning electrospinning processing parameters. The dictating process parameters on evolving structure are high voltage, tip to collector distance and solvent. Morphological and optical investigations suggest that uniform periodic topography helps in light scattering leading to multi reflection and thus enhancement in light absorption. This structure is evaluated as active layer in organic photovoltaic devices using poly (3 hexyl thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend and its device characteristics are analyzed. Consistent and reliable device characteristics obtained through photonic structure is demonstrated. Finally, comparison is drawn to network structure to assess the advantages and limitations of both morphologies as active layer in organic photovoltaics. In Chapter 5, instead of architecturing active layer the next polymer film layer in the organic solar cells, that is the hole transport layer is transformed into free standing nanofiber mats. Morphological, structural and surface wetting properties are assessed for these nanofiber mats followed by fabrication of inverted organic solar cell. The free standing nanofibers mats are obtained by electrospinning the blend of Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) a conducting water soluble polymer with other water soluble polymers such as poly vinyl alcohol (PVA) and poly ethylene oxide (PEO). The study is further extended by employing two batches of PEDOT:PSS of varying conductivity that are analyzed side by side for six ternary and two binary blends each. Electrospinning parameters such as applied voltage and flow rate are optimized and fibers of diameter 150-200 nm are obtained. Maximum content of PEDOT:PSS with which free standing fiber mats could be achieved are 98 and 99%. Subsequent increase in PEDOT:PSS results in formation of beads. Surface wetting behavior showed that hydrophillicity increases with increase in PEDOT:PSS content. Devices are fabricated and the variation in characteristics and charge collection with respect to addition of PEO and PVA are discussed. In Chapter 6, a conjugated small molecule is taken as case study unlike the use of the conjugated polymer studies in previous chapters. A mechanism is proposed for tuning the sphere-spike morphology and also to control the crystallite size through solvent management using a conjugated small molecule. Electrospraying of an organic molecule is carried out using various solvents, obtaining fibril structures along with a range of distinct morphologies. Solvent characteristics play a major role in achieving the morphology of the organic material. A thiophene derivative (7, 9-di (thiophen-2-yl)-8H-cyclopenta [a]acenaphthylen-8-one) (DTCPA) of donor-acceptor-donor (DAD) architecture is used to study this solvent effect. Seven solvents with decreasing vapor pressure are selected for experiments. Electrospraying is conducted at a solution concentration of 1.5 wt % and a constant applied voltage of 15 kV. Gradual transformation in morphology of the electrospun product from spikes-sphere to only spikes is observed. A mechanism describing this transformation is proposed based on the electron micrograph analysis and XRD analysis. These data indicate that the morphological change is due to the synergistic effect of both vapor pressure and dielectric constant of the solvents. Through a reasonable control over the crystallites size and morphology along with supporting transformation mechanism theory, the work in this chapter elucidates electrospraying as a prospective method for designing the architectures in organic electronics. In Chapter 7, light management studies are carried out by morphologically architecturing the carbazole derivatives through electrospraying. The effect of derivatives on morphology is analyzed. The two carbazole derivatives; carbazole-benzothiadiazole (Cz-Bz) resulted in 2D structures and carbazole-benzothiadiazole-bithiophene (Cz-Bz-Bt) resulted in 3D structures after electrospraying. These structures are further analyzed to study the effect of vapor pressure of solvents and solution concentration. Structural characteristics indicate that electrospraying imparts change in molecular structure orientation. Optical studies showed 19 – 31% enhancement in light absorption. Further, three types of organic photovoltaic devices are fabricated and the opto-electrical properties are evaluated. Also, the effect of substrate on morphological formation is assessed. In Chapter 8, the major contributions and conclusions drawn from the morphological architecturing of both conjugated polymers and small molecules are summarized, along with few recommendations for future research.

La pile à combustible microbienne, MFC, est un bioengine qui associe respectivement le principe biochimique et le principe électrochimique pour extraire les électrons stockés dans la matière organique et les transformer en électricité. Dans un MFC, des microbes électroactifs vivants, avec son système enzymatique complet, sont utilisés pour biocatalyser l'oxydation du combustible organique; une anode est introduite artificiellement pour détourner les électrons, ce qui a eu pour résultat le système respiratoire bactérien; et à l'opposé, une cathode entraîne le flux d'électrons qui est ensuite commuté sur le courant électrique. Les microbes électroactifs se répandent dans de nombreuses sources telles que le sol, le compost, les boues, les eaux usées, etc. Les aliments pour animaux, les combustibles organiques et / ou d'autres nutriments peuvent également être abondamment présents dans leurs sources matricielles et dans de nombreuses autres sources inestimables, couramment disponibles dans la vie quotidienne. L'abondance bactérienne et le carburant organique illimité sont les deux raisons attrayantes pour le développement d'une source d'énergie durable telle que le MFC, qui attire également notre attention dans cette recherche. Ici, nous avons développé MFC, double chambre (DCMFC) et chambre unique (SCMFC), alimentés par compost de jardin comme source électroactive et acétate de carburant. Pour des raisons de durabilité et d’autres avantages, c’est-à-dire praticables et respectueux de l’environnement, nous nous sommes principalement concentrés sur le SCMFC avec un système de cathodes respiratoires. La problématique commune du SCMFC est la production d’énergie limitée due principalement à la cinétique lente de la réaction de réduction de l’oxygène (ORR) dans la partie cathodique. Par conséquent, il est important de mettre au point le matériau de la cathode respiratoire qui présente une activité de catalyse appropriée vis-à-vis de la perte de réponse optique pour surmonter cette limitation. Le feutre de carbone (CF) est le matériau de support choisi qui convient à la fabrication de cathodes à respiration aérienne. Alors que le platine (Pt) et l’oxyde de manganèse (MnOx), respectivement, en tant que classe de catalyseur suprême et de second rang, ont été développés sur CF grâce à une méthode simple d’électrodéposition. Les matériaux résultants, dénommés ACF@Pt et ACF@MnOx, ont été caractérisés de manière complète par des méthodes électrochimiques et physicochimiques afin de déterminer leurs performances électrocatalytiques, supportant ainsi l’application de cathodes respiratoires. En conséquence, nous avons développé deux principaux types de cathodes respiratoires, à savoir ACF@Pt et ACF@MnOx, appliquées avec succès dans le SCMFC alimenté par du compost de jardin avec une densité de puissance respective de 140 mW m-2 et 110 mW m-2. De plus, les deux matériaux développés révèlent également des applications prometteuses. Par exemple, ACF@Pt a été utilisé comme anode de MFC, à la fois dans DCMFC et SCMFC, et a amélioré la densité de puissance jusqu'à 300 mW m-2. Fait intéressant, il est également montré comme un excellent électrocatalyseur dans la réaction de dégagement d’hydrogène, HER. Alors que le matériau ACF@MnOx présente un électrocatalyseur prometteur dans un système de type électro-Fenton à la minéralisation d'un matériau biréfractif, c'est-à-dire l'un des constituants polluants dangereux des eaux usées. / Microbial fuel cell, MFC, is a bioengine that combine biochemical and electrochemical principle respectively to extract the stored electrons in organic material and to turn them into electricity. In an MFC, living electroactive microbes, with its whole enzymatic system, are employed to biocatalyze the oxidation of organic fuel; an anode is artificially introduced to divert the electrons, as resulted in the bacterial respiratory system; and oppositely a cathode drives the electron flow that further be switched to electrical power. Electroactive microbes spread out in numerous sources such as soil, compost, sludge, waste water, and so on. The feed, organic fuel and/or other nutrient, also can abundantly be present in their matrix sources and in many other priceless sources, which commonly available in daily life. Bacterial abundance and unlimited organic fuel are the two attractive reasons for the development of sustainable energy source as such as MFC, which is also drawn our attention in this research. Herein, we developed MFC, double chamber (DCMFC) and single chamber (SCMFC), which powered by garden compost as electroactive source and acetate fuel. For sustainability reason and other advantages i.e. practicability and eco-friendly, we mainly focused on SCMFC with air-breathing cathode system. The common problematic of the SCMFC is the limited power production that mainly due to the slow kinetic of oxygen reduction reaction (ORR) in the cathodic part. Therefore, it is important to developed the material of air-breathing cathode which has a proper catalysis activity toward ORR to overcome this limitation. Carbon felt (CF) is the selected support material that suitable for air-breathing cathode fabrication. While, platinum (Pt) and manganese oxide (MnOx) respectively, as supreme and runner-up catalyst’s class, has been grown on CF through a simple electrodeposition method. The resulting materials, named as ACF@Pt and ACF@MnOx, have been characterized comprehensively by electrochemical and physicochemical methods to determine their electrocatalytic performances, which support for air-breathing cathode application. Accordingly, we have developed two main types of air-breathing cathode, i.e. ACF@Pt and ACF@MnOx, which have been successfully applied in SCMFC powered by garden compost with generated power density respectively 140 mW m-2 and 110 mW m-2. Moreover, the both developed material also reveal some promising application. For instance, ACF@Pt has been applied as MFC’s anode, both in DCMFC and SCMFC, and has improved the power density up to 300 mW m-2. Interestingly, it is also shown as an excellent electrocatalyst in hydrogen evolution reaction, HER. While, the ACF@MnOx material shows a promising electrocatalyst in an electro-Fenton like system to mineralization of biorefractory material i.e. one of the hazardous pollutant constituent of wastewater.

Cette thèse est consacrée à la synthèse de complexes 3d homo et hétérométalliques avec des ligands bases de Schiff ou dérivés de la 1,2,4,5-tétrazine, à l’investigation de leur structure et de leurs propriétés physico-chimiques. Ce travail peut être divisé en trois parties. Dans la première partie, nous nous sommes principalement concentrés sur les ligands bases de Schiff, dérivés du salicylaldéhyde et des aminoalcools, formés in situ. Treize complexes hétérométalliques ont été obtenus et entièrement caractérisés. Il a été montré que les composés synthétisés possèdent une activité catalytique dans la réaction de l’oxydation photochimique de l’eau, présentent des propriétés de photoconductive dans les polymères composites et peuvent être utilisés pour le développement de matériaux multifonctionnels. La deuxième partie décrit la fonctionnalisation des ligands base de Schiff par l’introduction dans leur structure des unités tétrathiafulvalène et métaux dithiolènes électroactives. Deux nouvelles familles de ligands ont été synthétisées et caractérisées. La série de sels de radicaux cations et de complexes dithiolènes homo et hétérométalliques ainsi que leurs propriétés physiques ont été discutées. La dernière partie est consacrée aux ligands à base de tétrazine. Les principaux avantages du noyau tétrazine ont été discutés. Deux nouveaux ligands dérivés de la picolylamine et leurs complexes 3d mono- et binucléaires ont été décrits. / The thesis is devoted to the synthesis of homo- and heterometallic 3d-metal complexes with Schiff base ligands or derivatives of 1,2,4,5- tetrazine, together with the investigation of their structural and physico-chemical properties. This work can be divided in three parts. In the first part we have been mainly focused on the Schiff base ligands, derivatives of the salicylaldehyde and aminoalcohols. Thirteen heterometallic complexes were obtained and fully characterized. It has been shown that the synthesized compounds possess catalytic activity in the photochemical water oxidation, exhibit photoconducting properties in polymeric composites and can be used for the development of multifunctional materials of wide use. The second part describes the functionalization of Schiff base ligands by the introduction into their structure of electroactive tetrathiafulvalene and dithiolate moieties. Two new families of ligands were synthesized and characterized. The series of radicalcation salts and homo- and heterometallic dithiolene complexes together with the investigation of their physical properties have been described. The last part is devoted to the tetrazine based ligands. The main advantages of the tetrazine ring have been discussed. Two new ligands, derivative of picolylamine and their mono- and binuclear 3d-metal complexes are reported. In conclusion, perspectives of further research related to the described results were highlighted.

Les microorganismes sont capables d'augmenter le potentiel libre des aciers inoxydables en eau de mer via un phénomène que l’on appelle anoblissement. Cette élévation de plusieurs centaines de millivolts du potentiel augmente le risque de corrosion localisé. L’anoblissement a été étudié pendant plus de 40 ans, et malgré son importance, les mécanismes microbiens responsables du phénomène n’ont pas été identifiés. Nous avons combiné l’écologie microbienne et l'électrochimie pour étudier la diversité des bactéries associées à l’anoblissement des aciers inoxydables. La température de l’eau de mer ainsi que la teneur en oxygène dissous sont des facteurs qui influencent l’anoblissement et nous les avons utilisés pour identifier la fraction bactérienne associée au changement de potentiel. L’anoblissement est inhibé par une température critique de l’eau de mer (au-dessus de 38°C/40°C) et par une teneur basse en oxygène dissous. A l’aide du séquençage d’amplicons ADN, nous avons identifié des unités taxonomiques opérationnels (OTUs) comme biomarqueurs de l’anoblissement. Certaines étaient affiliées à des bactéries capables de dégrader des hydrocarbures, et une OTU était affiliée à ‘Candidatus Tenderia electrophaga’, une bactérie électrotrophe capable de réduire l'oxygène avec des électrons provenant d’une électrode. Nous avons étudié le rôle de ces bactéries avec des conditions a potentiels fixés et libres avec une approche de métagénomique. Nous avons reconstitué un génome issu d’assemblage métagénomique (MAG) très proche de ‘Candidatus Tenderia electrophaga’ et associé à l'anoblissement. Avec ces résultats, nous avons proposé un nouveau mécanisme bactérien pour expliquer l’anoblissement : les bactéries électrotrophes seraient capables de réduire de l’oxygène avec des électrons provenant du film passif de l’acier inoxydable, et ainsi influencer le potentiel libre et donc l’anoblissement. / Microorganisms increase the opencircuit potential of stainless Steel immersed in seawater in a phenomenon called ennoblement.This change of potential of several hundreds of millivolts raises the chance of localized corrosion.The ennoblement has been studied for more than 40 years, and despite the importance and impact of ennoblement, little is known about the microbial mechanisms responsible for the phenomenon. We have combined microbial ecology and electrochemistry to investigate the diversity of surface attached bacteria associated with stainless steel ennoblement. Seawater temperature and dissolved oxygen content are factors that influence the ennoblement and we used them to infer the bacterial fraction associated with the phenomenon. The ennoblement is inhibited by a critical seawater tempzrature (above 38°C/40°C) and low dissolved oxygen content.With DNA amplicon sequencing, we identified operational taxonomie units (OTUs) that were biomarkers of the ennoblement. There were some OTUs affiliated to hydrocarbon degrading bacteria, and one OTU affiliated to ‘Candidatus Tenderia electrophaga’, an electrotrophic bacteria able to reduce oxygen with electrons from an electrode.We investigated the role of electrotrophic bacteria with potentiostatic and open circuit conditions and with metagenomics we recovered a metagenome assembled genome (MAG) very close to 'Candidatus Tenderia electrophaga’ associated with the ennoblement.From these results, we proposed a new bacterial mechanism to explain the ennoblement : electrotrophic bacteria would be able to reduce oxygen with électron drawn from the stainless steel passivation film, hence influencing the open circuit potential and therefore the ennoblement.

Piezoelectric materials are very useful for applications in sensors and actuators. In addition to traditional ferroelectric ceramics and ferroelectric polymers, ferroelectrets have recently become a new group of piezoelectrics. Ferroelectrets are functional polymer systems for electromechanical transduction, with elastically heterogeneous cellular structures and internal quasi-permanent dipole moments. The piezoelectricity of ferroelectrets stems from linear changes of the dipole moments in response to external mechanical or electrical stress. Over the past two decades, polypropylene (PP) foams have been investigated with the aim of ferroelectret applications, and some products are already on the market. PP-foam ferroelectrets may exhibit piezoelectric d33 coefficients of 600 pC/N and more. Their operating temperature can, however, not be much higher than 60 °C. Recently developed polyethylene-terephthalate (PET) and cyclo-olefin copolymer (COC) foam ferroelectrets show slightly better d33 thermal stabilities, but usually at the price of smaller d33 values. Therefore, the main aim of this work is the development of new thermally stable ferroelectrets with appreciable piezoelectricity. Physical foaming is a promising technique for generating polymer foams from solid films without any pollution or impurity. Supercritical carbon dioxide (CO2) or nitrogen (N2) are usually employed as foaming agents due to their good solubility in several polymers. Polyethylene propylene (PEN) is a polyester with slightly better properties than PET. A “voiding + inflation + stretching” process has been specifically developed to prepare PEN foams. Solid PEN films are saturated with supercritical CO2 at high pressure and then thermally voided at high temperatures. Controlled inflation (Gas-Diffusion Expansion or GDE) is applied in order to adjust the void dimensions. Additional biaxial stretching decreases the void heights, since it is known lens-shaped voids lead to lower elastic moduli and therefore also to stronger piezoelectricity. Both, contact and corona charging are suitable for the electric charging of PEN foams. The light emission from the dielectric-barrier discharges (DBDs) can be clearly observed. Corona charging in a gas of high dielectric strength such as sulfur hexafluoride (SF6) results in higher gas-breakdown strength in the voids and therefore increases the piezoelectricity. PEN foams can exhibit piezoelectric d33 coefficients as high as 500 pC/N. Dielectric-resonance spectra show elastic moduli c33 of 1 − 12 MPa, anti-resonance frequencies of 0.2 − 0.8 MHz, and electromechanical coupling factors of 0.016 − 0.069. As expected, it is found that PEN foams show better thermal stability than PP and PET. Samples charged at room temperature can be utilized up to 80 − 100 °C. Annealing after charging or charging at elevated temperatures may improve thermal stabilities. Samples charged at suitable elevated temperatures show working temperatures as high as 110 − 120 °C. Acoustic measurements at frequencies of 2 Hz − 20 kHz show that PEN foams can be well applied in this frequency range. Fluorinated ethylene-propylene (FEP) copolymers are fluoropolymers with very good physical, chemical and electrical properties. The charge-storage ability of solid FEP films can be significantly improved by adding boron nitride (BN) filler particles. FEP foams are prepared by means of a one-step procedure consisting of CO2 saturation and subsequent in-situ high-temperature voiding. Piezoelectric d33 coefficients up to 40 pC/N are measured on such FEP foams. Mechanical fatigue tests show that the as-prepared PEN and FEP foams are mechanically stable for long periods of time. Although polymer-foam ferroelectrets have a high application potential, their piezoelectric properties strongly depend on the cellular morphology, i.e. on size, shape, and distribution of the voids. On the other hand, controlled preparation of optimized cellular structures is still a technical challenge. Consequently, new ferroelectrets based on polymer-layer system (sandwiches) have been prepared from FEP. By sandwiching an FEP mesh between two solid FEP films and fusing the polymer system with a laser beam, a well-designed uniform macroscopic cellular structure can be formed. Dielectric resonance spectroscopy reveals piezoelectric d33 coefficients as high as 350 pC/N, elastic moduli of about 0.3 MPa, anti-resonance frequencies of about 30 kHz, and electromechanical coupling factors of about 0.05. Samples charged at elevated temperatures show better thermal stabilities than those charged at room temperature, and the higher the charging temperature, the better is the stability. After proper charging at 140 °C, the working temperatures can be as high as 110 − 120 °C. Acoustic measurements at frequencies of 200 Hz − 20 kHz indicate that the FEP layer systems are suitable for applications at least in this range. / Piezoelektrische Materialien haben große technische und wirtschaftliche Bedeutung für Anwendungen in Sensoren und Aktuatoren. Neben den traditionellen ferroelektrischen Keramiken und Polymeren bilden Ferroelektrete eine neue Gruppe der Piezoelektrika. Ferroelektrete sind reversible funktionelle Polymersysteme zur Umwandlung von elektrischer in mechanische Energie und umgekehrt. Sie zeichnen sich aus durch eine elastische zelluläre Struktur mit internen quasi-permanenten Dipolen. Der Mechanismus der Piezoelektrizität in Ferroelektreten wird dominiert von der Änderung der einzelnen Dipolmomente bei Einwirkung einer äußeren mechanischen Kraft. Insbesondere zelluläres Polypropylene (PP) war in den vergangenen zwei Jahrzehnten Gegenstand intensiver Forschung und Entwicklung im Hinblick auf die grundlegenden Eigenschaften und Anwendungen von Ferroelektreten. Einige bereits erhältliche kommerzielle Produkte nutzen die in geladenem zellulären PP erreichbaren hohen piezoelektrischen d33-Koeffizienten von 600 pC/N und mehr, sind aber durch eine relativ geringe maximale Betriebstemperatur von ungefähr 60 °C eingeschränkt. Die kürzlich entwickelten Ferroelektrete aus zellulärem Polyethylenterephthalat (PET) und zellulären Cyclo-Olefin-Copolymeren (COC) zeigen eine bessere Temperaturbeständigkeit (vor allem COC), allerdings gewöhlich auf Kosten von geringeren d33-Koeffizienten. Das Ziel der vorliegenden Arbeit ist es, temperaturbeständige Ferroelektrete mit für den Markt geeigneten piezoelektrischen Eigenschaften zu entwickeln. Physikalisches Schäumen ist eine beliebte Methode, um besonders reine Polymerschäume herzustellen. Häufig werden, wegen ihrer guten Löslichkeit in vielen Polymeren, Kohlenstoffdioxid (CO2) und Stickstoff (N2) im superkritischen Zustand als Treibmittel eingesetzt. Der Polyester Polyethylennaphtalat (PEN) hat ähnliche Eigenschaften wie PET, ist jedoch temperaturbeständiger. Ein Dreistufenprozess (Schäumen, Aufblähen und Strecken) wurde entwickelt, um PEN-Schäume für hochwertige Ferroelektrete herzustellen. Ungeschäumte PEN-Folien werden mit superkritischem CO2 unter hohem Druck gesättigt und anschließend unter geringem Druck bei Temperaturen nahe der Glastemperatur geschäumt. Um die Hohlräume zu vergrößern, wird der Schaum anschließend mittels Gasdiffusionsexpansion (GDE) aufgebläht. Nach zusätzlichem biaxialen Verstrecken erhält man die optimalen linsenförmigen Zellen, welche zu einer minimalen mechanischen Steifigkeit und einem maximalen piezoelektrischen d33-Koeffizienten des Ferroelektrets führen. Sowohl Korona- als auch Kontaktaufladung werden an zellulärem PEN erfolgreich eingesetzt. Die Lichtemission der dielektrisch behinderten Entladungen (DBDs) kann klar beobachtet werden. Korona-Aufladung in Gasen mit hohen dielektrischen Durchbruchsfestigkeiten, wie z.B. Schwefelhexafluorid (SF6), ermöglicht es, das Paschen-Durchbruchsfeld in den Hohlräumen und damit die erzielbare interne Ladungsdichte zu erhöhen. Dadurch können für zelluläres PEN piezoelektrische d33-Koeffizienten bis zu 500 pC/N erzielt werden. Piezoelektrischen Resonanzmessungen der Ferroelektrete liefern Steifigkeiten c33 im Bereich von 1 – 12 MPa, Antiresonanzfrequenzen von 0.2 – 0.8 MHz und elektromechanische Kopplungsfaktoren zwischen 0.016 und 0.069. PEN-Ferroelektrete zeigen eine bessere Temperaturstabilität als solche aus PP und PET. Der Anwendungsbereich von unbehandeltem PEN reicht bis etwa 80 – 100°C, jener von getemperten oder bei 120°C geladenen Proben bis etwa 110 – 120 °C. Akustische Messungen im Frequenzbereich von 2 Hz – 20 kHz zeigen die Eignung von PEN-Ferroelektretwandlern für Luftschallanwendungen. Fluoriertes Ethylen-Propylen (FEP) ist ein Fluorpolymer mit sehr guten physikalischen, chemischen und elektrischen Eigenschaften. Die Ladungsspeichereigenschaften von ungeschäumtem FEP können durch die Beimengung von Bornitrid deutlich verbessert werden. In dieser Arbeit wird zelluläres FEP mittels eines einstufigen Prozesses, dem schon erwähnten Schäumen mit überkritischem CO2, hergestellt. Die geladenen FEP-Proben weisen d33-Koeffizienten von bis zu 40 pC/N auf. Ermüdungstests zeigen eine sehr gute mechanische Stabilität von PEN- und FEP-Ferroelektreten. Zelluläre Polymerferroelektrete haben großes Potenzial für Anwendungen, und die Suche nach geeigneten zellulären Morphologien ist eng verknüpft mit dem technischen Aufwand ihrer Herstellung. Alternativ wurden Ferroelektrete mit Sandwich-Strukturen aus FEP-Folien entwickelt. Durch Laserverschmelzen eines FEP-Foliengitters mit zwei umgebenden FEP-Folien wird eine definierte, einheitliche zelluläre Struktur gebildet. Aus dielektrischen Resonanzspektren können effektive piezoelektrische d33-Koeffizienten bis zu 350 pC/N, effektive mechanische Steifigkeiten um 0.3 MPa, Antiresonanzfrequenzen um 30 kHz und elektromechanische Kopplungsfaktoren von etwa 0.05 abgeleitet werden. Proben, welche bei erhöhter Temperatur geladen werden, zeigen höhere Ladungsstabilitäten. Nach geeigneter Aufladung bei 140 °C kann die Arbeitstemperatur bis auf 110 – 120 °C gesteigert werden. Akustische Messungen im Frequenzbereich von 2 Hz – 20 kHz zeigen die Eignung von FEP-Sandwich-Strukturen für Luftschallanwendungen.

<p>Regenerative medicine holds the promise of providing relief for people suffering from diseases where treatment has been unattainable. The research is advancing rapidly; however, there are still many hurdles to overcome before the therapeutic potential of regenerative medicine and cell therapy can be realized. Low in frequency in all tissues, stem cell number is often a limiting factor. Approaches that can control the proliferation and direct the differentiation of stem cells would significantly impact the field. Developing an adequate environment that mimics in vivo conditions is an intensively studied topic for this purpose. Collaboratively, researchers have come close to incorporating nearly all biological cues representative of the human body. Arguably the most overlooked aspect is the influence of electrical stimulation. In this dissertation, we examined polyvinylidene fluoride (PVDF) as a new biomaterial and developed a 3D scaffold capable of providing mechanical and electrical stimuli to cells in vitro. </p><p>The fabrication of a 3D scaffold was performed using electrospinning. To obtain highly aligned fibers and scaffolds with controlled porosity, the set-up was modified by incorporating an auxiliary electrode to focus the electric field. Highly aligned fibers with diameters ranging from 500 nm to 15 µm were fabricated from colorless polyimide (CP2) and polyglycolic acid (PGA) and used to construct multilayer scaffolds. This experimental set-up was used to electrospin &#945;-phase PVDF into the polar &#946;-phase. We demonstrated the transition to the &#946;-phase by examining the crystalline structure using x-ray diffraction (XRD), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR) and polarized light optical microscopy (PLOM). We confirmed these results by observing a polarization peak at 80°C using the thermally stimulated current (TSC) method. Our results proved the electrospinning process used in our investigation poled the PVDF polymer in situ. </p><p>TThe influence of architecture and topographical cues was examined on 3D scaffolds and films of CP2 polyimide and PVDF. Culture of human mesenchymal stem cells (hMSCs) for 7 and 14 days demonstrated a significant difference in gene expression. The fibers upregulated the neuronal marker microtubule associated protein (MAP2), while downregulation of this protein was observed on films. Gap junction formation was observed by the expression of connexin-43 after 7 days on PVDF films attributed to its inherent pyroelectric properties. Connexin-43 expression on fibers showed cell-cell contact across the fibers indicating good communication in our 3D scaffold. </p><p>A scaffold platform was designed using PVDF fibers that allowed us to apply electrical stimulation to the cells through the fibers. The electrically stimulated PVDF fibers resulted in enhanced proliferation compared to TCPS as evidenced by a 10% increase in the uptake of EdU. Protein expression revealed upregulation of neuronal marker MAP2. Our findings indicate this new platform capable of delivering mechanical, electrical, topographical and biochemical stimuli during in vitro culture holds promise for the advancement of stem cell differentiation and tissue engineering.</p> / Dissertation

This thesis presents a preliminary design of a fully articulated five-fingered anthropomorphic human hand prosthesis with particular emphasis on the controller and actuator design. The proposed controller is a modified artificial neural network PID-based controller with application to the nonlinear and highly coupled dynamics of the hand prosthesis. The new solid state actuator has been designed based on electroactive polymers, which are a type of material that exhibit electromechanical behavior and a liquid metal alloy acts as the electrode. The solid state actuators reduce the overall mechanical complexity, risk failure and required maintenance of the prosthesis. / Graduate

In this thesis, three different types of polymer-based gels are fabricated and characterized for passive and active applications. Silica aerogel is a 3D mesoporous solid material that can be used for thermal insulation or in the biomedical industry. In this thesis, silica aerogel is cross- linked with diisocyanate to improve its strength and flexibility, which greatly opens up the range of applications. Then, soft polymer gel with tissue equivalent characteristics is fabricated to mimic the spin-lattice (T1) and spin-spin (T2) relaxation times for the magnetic resonance imaging (MRI) phantom of a liver with lesions. This study demonstrates a relationship between the composition of a gelling agent, and T1 and T2 modifiers on its dielectric, mechanical and imaging properties. Finally, an ionic electroactive polymer (EAP) that can be actuated on an electric field is fabricated, and its swelling and bending behaviours on design parameters are closely examined.

In this thesis, three different types of polymer-based gels are fabricated and characterized for passive and active applications. Silica aerogel is a 3D mesoporous solid material that can be used for thermal insulation or in the biomedical industry. In this thesis, silica aerogel is cross- linked with diisocyanate to improve its strength and flexibility, which greatly opens up the range of applications. Then, soft polymer gel with tissue equivalent characteristics is fabricated to mimic the spin-lattice (T1) and spin-spin (T2) relaxation times for the magnetic resonance imaging (MRI) phantom of a liver with lesions. This study demonstrates a relationship between the composition of a gelling agent, and T1 and T2 modifiers on its dielectric, mechanical and imaging properties. Finally, an ionic electroactive polymer (EAP) that can be actuated on an electric field is fabricated, and its swelling and bending behaviours on design parameters are closely examined.

Electrical motors and/or hydraulics and pneumatics cylinders are commonly used methods of actuation in mechanical systems. Over the last two decades, due to arising market needs, novel self-independent mobile systems such as mobility assistive devices have emerged with the help of new advancements in technology. The actuation criteria for these devices differ greatly from typical mechanical systems, which has made the implementation of classical actuators difficult within modern assistive devices. Among the numerous challenges, limited energy storage capabilities by mobile systems have restricted their achievable operational time. Furthermore, new expectations for device weight and volume, as well as actuator structural compliance, have added to this quandary. Electroactive polymers, a category of smart materials, have emerged as a strong contender for the use in low-cost efficient actuators. They have demonstrated great potential in soft robotic and assistive device/prosthetic applications due to their actuation potential and similar mechanical behaviour to human skeletal muscles. Dielectric Elastomers, in particular, have shown very promising properties for these types of applications. Their structures have shown large achievable deformation, while remaining light-weight, mechanically efficient, and low-cost. This thesis aims to characterize, and model the behaviour of 3MTM VHB polyacrylic dielectric elastomer, in order to establish a foundation for its implementation in a proposed novel linear actuator concept. In this thesis, a comprehensive experimental evaluation is accomplished, which resulted in the better understanding of the elastomer’s biaxial mechanical and electro-mechanically coupled behaviours. Subsequently, a constitutive biaxial mechanical model was derived in order to provide a predictive design equation for future actuator development. This model proved effective in providing a predictive tool for the biaxial mechanical tensile response of the material. Finally, a simplified prototype was devised as a proof of concept. This first iteration applied experimental findings to validate the working principles behind the proposed actuator design. The results confirmed the proof of concept, through achieved reciprocal linear motion, and provided insight into the design considerations for prototype optimization and final actuator development.