Polymers containing poly(1,3-cyclohexadiene) were synthesized using a novel pre-formed initiator comprised of an alkyllithium and a tertiary diamine. The use of a pre-formed intiator at moderate temperatures (25° C) enabled the synthesis of high molecular weight poly(1,3-cyclohexadiene) homopolymers (<Mn> = 50000) with narrow molecular weight distributions (<Mw>/<Mn> = 1.20). In contrast, the use of a conventional anionic initiation approach resulted in polymerizations that lacked significant degrees of livingness, which limited the polymer molecular weights to approximately 10000. Use of the preformed initiator resulted in a reduction in the degree of both chain termination and chain transfer. In addition, the livingness of the polymerization was shown to be a function of the monomer concentration and the polymerization temperature. The regiochemistry of the polymers were shown to be dependent on the tertiary amine used in the polymerization, which provided a route for the synthesis of polymers with a microstructure rich in either high 1,2-addition (70%) or high 1,4-addition (90%). A range of analytical methods were employed to determine the stereo and regiochemistry of poly(1,3-cyclohexadiene). These methods included 1H NMR, 13C NMR, and endgroup functionalization of the propagating center with chlorotrimethylsilane. The impact of regiochemistry on the thermal properties was examined using differential scanning calorimetry. In addition, the thermooxidative properties of these poly(1,3-cyclohexadiene) polymers were characterized in a series of oxidative studies and the onset of oxidative degradation occurred at 110° C. Perfectly alternating copolymers of poly(1,3-cyclohexadiene-alt-styrene) were synthesized, and the reactivity ratios for these copolymers (r1,3CHD = 0.022, rstyrene = 0.024) were determined using a conventional Mayo-Lewis approach. The effect of aromatization and hydrogenation on the thermal properties of these copolymers was determined using thermal gravimetric analysis and differential scanning calorimetry. The synthesis of poly(1,3-cyclohexadiene) DVB coupled star-shaped polymers was performed using a convergent arm-first approach in combination with a divinylbenzene coupling agent (PDI = 1.25). Well-defined poly(1,3-cyclohexadiene-block-isoprene)-star shaped polymers were synthesized and utilized for the development of novel high temperature thermoplastic elastomers, with excellent elastomeric properties (percent elongation = 745 %, tensile strength = 7.2 MPa). Atomic force microscopy in combination with differential scanning calorimetry verified the presence of microphase separation between the blocks. / Ph. D.

<p dir="ltr">Increasing power density and power consumption in electronic devices require heat dissipating components with high thermal conductivity to prevent overheating and improve performance and reliability. Polymers offer the advantages of low cost and weight over conventional metallic components, but their intrinsic thermal conductivity is low. Previous studies have shown that the thermal conductivity of polymers can be enhanced by aligning the polymer chains or by adding high thermal conductivity fillers to create percolation paths within the polymeric matrix. To further enhance the in-plane thermal conductivity, the conductive fillers can be aligned preferentially, but this leads to a lower increase in performance in the cross-plane direction. Yet, the cross-plane thermal conductivity plays a vital role in dissipating heat from active devices and transmitting it to the surrounding environment. Alternatively, when the fillers are aligned to enhance cross-plane thermal transport, the enhancement in the in-plane direction is limited. There is a need to develop polymer composites with an approximately isotropic increase in thermal performance compared to their neat counterparts.</p><p dir="ltr">To achieve this goal, in this study, I combine conductive fibers and fillers to enhance thermal conductivity of polymers without significantly inducing thermal anisotropy while preserving the mechanical performance of the matrix. I employ three approaches to enhance the thermal conductivity () of thermoset polymeric matrices. In the first approach, I fabricate thermally conductive polymer composites by creating an emulsion consisting of eutectic gallium indium alloy (EGaIn) liquid metal in the uncured polydimethylsiloxane (PDMS) matrix. In the second approach, I infiltrate mats formed from chopped fibers of Ultra High Molecular Weight Polyethylene (UHMWPE) with an uncured epoxy resin. Finally, the third approach combines the two previous methods by infiltrating the UHMWPE fiber mat with an emulsion of the liquid metal and uncured epoxy matrix.</p><p dir="ltr">To evaluate the thermal performance of the composites, I use infrared thermal microscopy with two different experimental setups, enabling independent measurement of in-plane and cross-plane thermal conductivity. The results demonstrate that incorporating thermally conductive fillers enhances the overall conductivity of the polymer composite. Moreover, I demonstrate that the network structure achieved by the fiber mat, in combination with the presence of liquid metal, promotes a more uniform increase in the thermal conductivity of the composite in all directions. Additionally, I assess the impact of filler incorporation and filler concentration on matrix performance through tension, indentation, and bending tests for mechanical characterization of my materials.</p><p dir="ltr">This work demonstrates the potential of strategic composite design to achieve polymeric materials with isotropically high thermal conductivity. These new materials offer a solution to the challenges posed by higher power density and consumption in electronics and providing improved heat dissipation capabilities for more reliable devices.</p>

The modification of polymeric materials using plasticizers or elastomers has been investigated in three research programs. The first describes epoxy resins modified with dimethylsiloxane, dimethyl-co-methyltrifluoropropyl siloxane, and dimethyl-co-diphenyl siloxane. The apparent compatibility between the epoxy and the siloxanes was enhanced by increasing methyltrifluoropropyl or diphenyl siloxane content or lowering molecular weight, resulting in profound changes in morphology and the resultant mechanical properties of the modified resins. Fracture toughness was most significantly improved using siloxanes containing at least 40% methyltrifluoropropyl siloxane or 20 and 40% diphenyl siloxane. Comparison of siloxane modifiers with butadiene acrylonitrile modifiers was valuable with regard to both property and morphological effects. The second research project considers the structure-property behavior of polyvinyl chloride (PVC) plasticized with low molecular weight diesters with emphasis on the contrasting effects of different plasticizers on the breadth of PVC's dynamic mechanical spectrum. It was clearly demonstrated that a less soluble plasticizer promoted a greater broadening at intermediate concentrations. Crystallization phenomena and static mechanical properties reflected the greater diluent effect of a more soluble plasticizer. The dynamic mechanical behavior as well as other critical experimental observations were explained using a model which postulates that the network junctions of plasticized PVC consist of "pockets" containing several small crystallites. These pockets are randomly dispersed in a matrix whose homogeneity is governed by the plasticizer's solubility and molar volume. The third research project describes the modification of high 1,4 polybutadiene (PB) with isopropyl azodicarboxylate (IAD) for potential .use as impact modifiers for polar polymers. A method for finding the extent of IAD modification of the PB has been developed using ¹³C nmr and UV spectroscopy. Solution blends of PVC with PB modified with up to 11 mol% IAD were found to be immiscible. Stress-strain testing suggested that IAD modification (11%) enhanced the apparent compatibility between PB and PVC at 25% rubber content. The relatively poor mechanical response of the blends was believed to be related to their somewhat porous morphology. / Ph. D. / incomplete_metadata

Elektroakustische Systeme wie Lautsprecher, die elektrische Signale in akustische Signale umwandeln, sind heute Eckpfeiler der Kommunikation. Von Mikrotreibern in Kopfhörern und Smartphones über Audiosysteme in Fahrzeugen und Wohnzimmern bis hin zu großen Beschallungsanlagen in öffentlichen Räumen, Kinos und Konzerten sowie zahlreichen technischen Anwendungen sind sie heute ein allgegenwärtiger Bestandteil des täglichen Lebens. Die gängigsten Lautsprechertechnologien basieren auf elektrodynamischen Wandlern. Seit der ersten Patentierung vor 145 Jahren wurden diese, die notwendige Leistungselektronik sowie die Methoden zur Auslegung und Systembeschreibung im Klein- und Großsignalbereich kontinuierlich weiterentwickelt. Die Forschung befasst sich aber auch ständig mit alternativen Technologien, die Vorteile gegenüber konventionellen Antrieben haben können. In diesem Zusammenhang haben dielektrische Elastomere (DE) in den letzten 25 Jahren zunehmend an Aufmerksamkeit gewonnen. Sie versprechen u.a. einen höheren Wirkungsgrad, neuartige Konstruktionen und eine erhebliche Gewichtsreduktion. Zudem können sie aus kostengünstigen Ausgangsmaterialien ohne den Einsatz von Seltenen Erden oder ferroelektrischen Materialien hergestellt werden, was die Abhängigkeit von Rohstoffimporten verringert und neue Anwendungsfelder eröffnet. Trotz sehr aktiver Forschung und Entwicklung bei Materialien, Design und Herstellung gibt es bisher nur wenige kommerziell verfügbare Aktuatoranwendungen. Eine grundlegende Voraussetzung für die Etablierung einer Technologie sind standardisierte und nachvollziehbare Methoden zur prädiktiven Systembeschreibung und zum rechnergestützten Systementwurf. Diese sind für DE in dynamischen Anwendungen noch nicht verfügbar. In dieser Arbeit wird die etablierte Entwurfsmethodik zur prädiktiven Beschreibung kleinsignaliger dynamischer Systeme mit elektromechanischen und akustischen Netzwerken auf dielektrische Elastomere erweitert. Das Kernelement ist die Ableitung der elektromechanischen Wandlermodelle für DE-Längs- und Dickenoszillatoren. Basierend auf dieser Systembeschreibung, werden Auslegungskriterien für DE-basierte Schallquellen aufgestellt. Der Fokus liegt dabei auf der praktischen Anwendbarkeit und der Generierung von technologischen Vorteilen gegenüber elektrodynamischen Wandlern. Aus diesen Kriterien werden neuartige Wandlerkonzepte in Form von rollenaktorgetriebenen Lautsprechermembranen und unimorphen Membranen entwickelt, analysiert und als Demonstratoren realisiert. Darüber hinaus wird die Leistungselektronik untersucht, auf deren Basis Schaltungen zur Durchführung messtechnischer Untersuchungen und zum Betrieb der Demonstratoren entwickelt und realisiert wurden. Ziel der Arbeit ist es, Anwendungsentwicklern mit der vorgestellten Entwurfsmethodik einen besseren Zugang zur Technologie zu ermöglichen und so zur Entwicklung von DE-basierten Schallquellen im Speziellen und dynamischen DE-Aktoren im Allgemeinen beizutragen.:1 Introduction 1 2 Fundamentals of Dielectric Elastomers 5 3 Electromechanical Network Model of Dielectric Elastomers 9 3.1 Transducer Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.1 Electrostatic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1.2 Simulative-experimental Validation . . . . . . . . . . . . . . . . . . . . . . 14 3.1.3 Mechanical Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.4 Determination of the Parameters at the Operating Point . . . . . . . . . 19 3.1.5 Electromechanical Transducer Model . . . . . . . . . . . . . . . . . . . . . 23 3.2 Electrical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.3 Operating Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4 Mechanical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4 Power Electronics 37 4.1 Fundamental Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.2 Alternative Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.2.1 Adapted Circuit Designs for Capacitive Loads . . . . . . . . . . . . . . . . 39 4.2.2 Summing Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.3 Realization of Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.3.1 Coupling Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3.2 Branch to Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.3.3 Charging Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.3.4 Additional Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.3.5 Implemented Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . 46 5 Design of DE Loudspeakers 49 5.1 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 5.1.1 Membrane and Bubble-Loudspeakers . . . . . . . . . . . . . . . . . . . . 49 5.1.2 Annular Membrane Actuators . . . . . . . . . . . . . . . . . . . . . . . . . 52 5.1.3 Preformed Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 5.1.4 Thickness Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 5.2 Fundamental Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 55 5.3 Proposed Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 6 DE-Roll Actuator based Loudspeaker Driver 61 6.1 Fundamentals of DERA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 6.2 Stability Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 6.3 Model Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.3.1 Fundamental Implementation . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.4 Construction and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 6.4.1 PolyPower Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 VTable of Contents 6.4.2 Elastosil Actuator Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . 77 6.4.3 Overview of Manufactured Actuators . . . . . . . . . . . . . . . . . . . . . 78 6.5 Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.5.1 Static Function Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.5.2 Electrical Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.5.3 Dynamic Electromechanical Measurements . . . . . . . . . . . . . . . . . 83 6.6 Electromechanical Test Results and Model Updating . . . . . . . . . . . . . . . . 85 6.7 Radial Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.8 Acoustic Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.8.1 Acoustic Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.8.2 Selection of loudspeaker diaphragm . . . . . . . . . . . . . . . . . . . . . 92 6.8.3 Loudspeaker in Closed Cabinet . . . . . . . . . . . . . . . . . . . . . . . . . 96 6.8.4 Loudspeaker in Vented Cabinet . . . . . . . . . . . . . . . . . . . . . . . . 98 6.8.5 Bending Wave Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.9 Acoustic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.10 Demonstrator Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.11 Considerations towards Large-Signal Behaviour . . . . . . . . . . . . . . . . . . . 112 7 Dielectric Elastomer Unimorph Membrane 115 7.1 Membrane Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 7.2 Model-based Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 7.3 Headphones demonstrator construction . . . . . . . . . . . . . . . . . . . . . . . 119 7.4 Measurements and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 8 Summary and Outlook 129 Appendix 133 A ANSYS APDL simulation code for DE elementary cell model . . . . . . . . . . . . 136 B Additional comparisons of measurement and simulation data . . . . . . . . . . 138 / Electroacoustic systems such as loudspeakers, which convert electrical signals into acoustic signals, are nowadays cornerstones of communication. From microdrivers in headphones and smartphones, to audio systems in vehicles and living rooms, to large sound reinforcement systems in public spaces, cinemas and concerts, as well as numerous technical applications, they are nowadays a ubiquitous part of everyday life. The most common loudspeaker technologies are based on electrodynamic transducers. Since the first patent 145 years ago, they, the necessary power electronics as well as the methods for design and system description in the small- and large- signal range have been continuously developed. However, research is also constantly looking at alternative technologies that may have advantages over conventional drives. In this context, dielectric elastomers (DE) have gained increasing attention over the past 25 years. They promise, among other things, higher efficiency, novel designs and considerable weight reduction. Moreover, they can be manufactured from inexpensive starting materials without the use of rare-earths elements or ferroelectric materials, which reduces the dependence on raw materials imports and opens up new fields of application. Despite very active research and development of materials, designs and fabrication, there are only few commercially available actuator applications so far. A fundamental requirement for the establishment of a technology are standardized and comprehensible methods for predictive system description and for computer-aided system design. These are not yet available for DE in dynamic applications. In this work, the established design methodology for the predictive description of smallsignal dynamic systems using electromechanical and acoustic networks is being extended to dielectric elastomers. The core element is the derivation of the electromechanical transducer models for DE longitudinal and thickness oszillators. Based on this system description, design criteria for DE based sound sources are established. The focus lies on practical applicability and the generation of technological advantages compared to electrodynamic transducers. From these criteria, novel transducer concepts in the form of roll actuator driven loudspeaker diaphragms and unimorph membranes are developed, analyzed and realized as demonstrators. In addition, the power electronics are examined, on the basis of which circuits for carrying out metrological investigations and for operating the demonstrators were developed and implemented. The goal of the work is to provide application developers with better access to the technology using the presented design methodology and thus contribute to the development of DE-based sound sources in particular and dynamic DE actuators in general.:1 Introduction 1 2 Fundamentals of Dielectric Elastomers 5 3 Electromechanical Network Model of Dielectric Elastomers 9 3.1 Transducer Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.1 Electrostatic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1.2 Simulative-experimental Validation . . . . . . . . . . . . . . . . . . . . . . 14 3.1.3 Mechanical Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.4 Determination of the Parameters at the Operating Point . . . . . . . . . 19 3.1.5 Electromechanical Transducer Model . . . . . . . . . . . . . . . . . . . . . 23 3.2 Electrical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.3 Operating Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4 Mechanical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4 Power Electronics 37 4.1 Fundamental Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.2 Alternative Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.2.1 Adapted Circuit Designs for Capacitive Loads . . . . . . . . . . . . . . . . 39 4.2.2 Summing Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.3 Realization of Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.3.1 Coupling Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3.2 Branch to Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.3.3 Charging Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.3.4 Additional Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.3.5 Implemented Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . 46 5 Design of DE Loudspeakers 49 5.1 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 5.1.1 Membrane and Bubble-Loudspeakers . . . . . . . . . . . . . . . . . . . . 49 5.1.2 Annular Membrane Actuators . . . . . . . . . . . . . . . . . . . . . . . . . 52 5.1.3 Preformed Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 5.1.4 Thickness Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 5.2 Fundamental Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 55 5.3 Proposed Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 6 DE-Roll Actuator based Loudspeaker Driver 61 6.1 Fundamentals of DERA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 6.2 Stability Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 6.3 Model Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.3.1 Fundamental Implementation . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.4 Construction and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 6.4.1 PolyPower Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 VTable of Contents 6.4.2 Elastosil Actuator Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . 77 6.4.3 Overview of Manufactured Actuators . . . . . . . . . . . . . . . . . . . . . 78 6.5 Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.5.1 Static Function Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.5.2 Electrical Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.5.3 Dynamic Electromechanical Measurements . . . . . . . . . . . . . . . . . 83 6.6 Electromechanical Test Results and Model Updating . . . . . . . . . . . . . . . . 85 6.7 Radial Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.8 Acoustic Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.8.1 Acoustic Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.8.2 Selection of loudspeaker diaphragm . . . . . . . . . . . . . . . . . . . . . 92 6.8.3 Loudspeaker in Closed Cabinet . . . . . . . . . . . . . . . . . . . . . . . . . 96 6.8.4 Loudspeaker in Vented Cabinet . . . . . . . . . . . . . . . . . . . . . . . . 98 6.8.5 Bending Wave Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.9 Acoustic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.10 Demonstrator Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.11 Considerations towards Large-Signal Behaviour . . . . . . . . . . . . . . . . . . . 112 7 Dielectric Elastomer Unimorph Membrane 115 7.1 Membrane Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 7.2 Model-based Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 7.3 Headphones demonstrator construction . . . . . . . . . . . . . . . . . . . . . . . 119 7.4 Measurements and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 8 Summary and Outlook 129 Appendix 133 A ANSYS APDL simulation code for DE elementary cell model . . . . . . . . . . . . 136 B Additional comparisons of measurement and simulation data . . . . . . . . . . 138

The aim of the work reported here was to determine the influence of an amine curing agent, and postcure cycle on the mechanical and thermal properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The results of this initial study were then used as the basis for selecting material to obtain optimum toughness in epoxy/glass fibre systems. These basic materials were further used to make comparisons with the properties of modified resin systems which contained commercial elastomers. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA), Fourier Transform Infrared Spectroscopy (FTIR), flexural and interlaminar shear tests, Instrumented Falling Weight Impact (IFWI), visual observation, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were all used to investigate various properties and the structures which gave rise to them. The properties of cured products were found to be affected by the amounts of curing agent, curing times and temperatures, and the structure of the elastomers. Not surprisingly the maximum thermal and mechanical properties tended to be found in the stoichiometric (standard) mix systems. However, postcuring at higher than room temperature, which was used as the basic curing temperature, led to more conversion. This effect improved the thermal and mechanical properties of both the unmodified and modified resin systems. The maximum flexural strength of 104 MPa of the unreinforced resins was found in the stoichiometric mix ratio after postcure at 150°C for 4 hr. However, the maximum flexural modulus and glass transition temperature (Tg) were found after postcuring at the same temperature for 48 hr. This was believed to be due to increased crosslinking, but unfortunately the longer curing time led to degradation of the resins. In the systems modified with -20 phr of polyetheramine elastomers, the one modified with the lowest molecular weight (2000) was found to have the highest flexural strength (85.8 MPa) and modulus (2.5 GPa). The impact properties of all the composites with modified resin matrices were found to be higher than the unmodified resin matrix composites. The best impact properties were, however, obtained with the elastomer modifier with a molecular weight of 4000. The impact energy at maximum force increased from 11.9 to 16.4 J, and energy at failure increased from 18.7 to 21.6 J. This increase in impact properties was due to the increase in areas of phase separated elastomer particles over similar systems with lower molecular weight modifier.

O objetivo deste estudo foi propor a utilização de um novo silicone (Bio-Skin - BS) para prótese bucomaxilofacial. Foram analisadas alteração de cor, dureza Shore A, resistência à tração, características de superfície (MEV) e composição química (EDS) frente à diferentes pigmentações e envelhecimentos. Como parâmetro de comparação foi empregado o silicone MDX4-4210. Foram obtidos 120 espécimes para cada material com formato circular e 160 em forma de haltere, a partir de matrizes metálicas de corte, os quais foram distribuídos em 4 grupos: PI - pigmentação intrínseca (pó de maquiagem); OP - opacificador (sulfato de bário, BaSO4); PIO - associação de PI + OP; SP - sem adição de PI ou OP. Em seguida, os espécimes foram distribuídos aleatoriamente em 3 subgrupos para exposição ao envelhecimento por luz natural (LN, n=10), luz ultravioleta (UV, n=10) e ausência de luz (C, n=10). O período experimental foi de 12 meses. A alteração de cor foi verificada com auxílio de espectrocolorímetro e sistema CIE L*a*b*. Para a dureza foi utilizado um durômetro Shore A e a análise da resistência à tração foi realizada em máquina universal de ensaio. As variáveis de resposta quantitativas foram mensuradas imediatamente após a obtenção dos espécimes e após o período experimental. A análise de superfície foi realizada por microscopia eletrônica de varredura (MEV) e a composição química dos silicones, por espectroscopia por energia dispersiva (EDS). Os dados foram submetidos à análise de variância e teste complementar de Tukey (p<0,05). Os resultados das análises por MEV e EDS foram apresentados em imagens e gráficos. Houve interação entre todos os fatores (p<0,05) e ambos os materiais sofreram variações em função das pigmentações e envelhecimentos. Para alteração de cor, o silicone experimental (BS) apresentou as menores variações de cor. Analisando os silicones em função da pigmentação, o MDX apresentou maiores variações com os espécimes SP e com OP envelhecidos por luz natural e luz UV. Para o BS, houve alteração significativa da cor dos espécimes SP e OP somente após o envelhecimento por LN. Os dois materiais apresentaram aumento da dureza frente a todas as condições, sendo que o silicone BS apresentou a maior variação. O silicone experimental apresentou resistência à tração superior ao MDX em todas as situações. O MDX não sofreu influência significativa na resistência à tração por nenhuma das pigmentações ou envelhecimento, exceto quanto pigmentado com pó de maquiagem e envelhecido por UV, onde houve aumento da resistência. Quanto ao silicone BS, os maiores valores de resistência à tração foram encontrados com a PI e PIO em todos os grupos de envelhecimento. Pode-se considerar que o material experimental apresentou resultados favoráveis em relação à alteração de cor, dureza Shore A e resistência à tração para sua aplicação clínica em prótese bucomaxilofacial. A associação da pigmentação intrínseca, por meio de pó de maquiagem com opacificador, protegeu o silicone da alteração de cor e promoveu alterações aceitáveis nas propriedades mecânicas dos materiais. Todos os processos de envelhecimento promoveram alterações nas propriedades dos materiais. / The aim of this study was to propose the use of a new silicone (Bio-Skin - BS) for maxillofacial prosthesis. Color change, Shore A hardness, tensile strength, surface characteristics (SEM) and chemical composition (EDS) were analyzed, regarding different pigmentation and aging methods. The MDX4-4210 silicone was used as parameter of comparison. Specimens (120 circular and 160 dumbbell-shaped) were obtained for each material, from metal cutting molds, which were divided into 4 groups: IP - intrinsic pigmentation (makeup powder); OP - opacifier (barium sulfate, BaSO4); IPO - IP + OP association; WP - without adding IP or OP. Then, the specimens were randomly divided into 3 subgroups to aging by exposure to natural light (NL, n = 10), ultraviolet light (UV, n = 10) and without light (C, n = 10). The experimental period was 12 months. The color change was observed with spectrocolorimeter and CIE L*a*b* system. For hardness we used a Shore A durometer and the analysis of tensile strength was performed in a universal testing machine. The quantitative response variables were measured immediately after obtaining the specimens and after the experimental period. The surface analysis was performed by scanning electron microscopy (SEM) and the chemical composition of silicones, by energy dispersive spectroscopy (EDS). Data were submitted to ANOVA and Tukey\'s test (p <0.05). SEM and EDS results were presented in pictures and graphics. There was interaction between all factors (p <0.05) and both materials varied depending on the pigmentation and aging methods. For color change, the experimental silicone (BS) showed the lowest color variations. Analyzing the silicones due to the pigmentation, the MDX showed higher variation with the WP and OP specimens aged in natural light and UV light. For BS, there was significant change in the color of the WP and OP specimens only after aging for NL. The two materials presented an increase in hardness front of all conditions, and the BS silicone showed the greatest variation. The experimental silicone showed superior tensile strength to MDX in all situations. The MDX was not affected in tensile strength by any pigmentation or aging, except for the group pigmented with makeup powder and aged by UV, where there was an increase of resistance. As to BS silicone, the highest tensile strength values were found for the IP and IPO in all age groups. It can be considered that the experimental material showed favorable results regarding color change, Shore A hardness and tensile strength for clinical use in maxillofacial prosthesis. The association of intrinsic pigmentation through makeup powder and opacifier, protected silicone of color change and promoted acceptable changes in mechanical properties of the materials. All the aging processes promoted changes in material properties.

O objetivo deste estudo foi propor a utilização de um novo silicone (Bio-Skin - BS) para prótese bucomaxilofacial. Foram analisadas alteração de cor, dureza Shore A, resistência à tração, características de superfície (MEV) e composição química (EDS) frente à diferentes pigmentações e envelhecimentos. Como parâmetro de comparação foi empregado o silicone MDX4-4210. Foram obtidos 120 espécimes para cada material com formato circular e 160 em forma de haltere, a partir de matrizes metálicas de corte, os quais foram distribuídos em 4 grupos: PI - pigmentação intrínseca (pó de maquiagem); OP - opacificador (sulfato de bário, BaSO4); PIO - associação de PI + OP; SP - sem adição de PI ou OP. Em seguida, os espécimes foram distribuídos aleatoriamente em 3 subgrupos para exposição ao envelhecimento por luz natural (LN, n=10), luz ultravioleta (UV, n=10) e ausência de luz (C, n=10). O período experimental foi de 12 meses. A alteração de cor foi verificada com auxílio de espectrocolorímetro e sistema CIE L*a*b*. Para a dureza foi utilizado um durômetro Shore A e a análise da resistência à tração foi realizada em máquina universal de ensaio. As variáveis de resposta quantitativas foram mensuradas imediatamente após a obtenção dos espécimes e após o período experimental. A análise de superfície foi realizada por microscopia eletrônica de varredura (MEV) e a composição química dos silicones, por espectroscopia por energia dispersiva (EDS). Os dados foram submetidos à análise de variância e teste complementar de Tukey (p<0,05). Os resultados das análises por MEV e EDS foram apresentados em imagens e gráficos. Houve interação entre todos os fatores (p<0,05) e ambos os materiais sofreram variações em função das pigmentações e envelhecimentos. Para alteração de cor, o silicone experimental (BS) apresentou as menores variações de cor. Analisando os silicones em função da pigmentação, o MDX apresentou maiores variações com os espécimes SP e com OP envelhecidos por luz natural e luz UV. Para o BS, houve alteração significativa da cor dos espécimes SP e OP somente após o envelhecimento por LN. Os dois materiais apresentaram aumento da dureza frente a todas as condições, sendo que o silicone BS apresentou a maior variação. O silicone experimental apresentou resistência à tração superior ao MDX em todas as situações. O MDX não sofreu influência significativa na resistência à tração por nenhuma das pigmentações ou envelhecimento, exceto quanto pigmentado com pó de maquiagem e envelhecido por UV, onde houve aumento da resistência. Quanto ao silicone BS, os maiores valores de resistência à tração foram encontrados com a PI e PIO em todos os grupos de envelhecimento. Pode-se considerar que o material experimental apresentou resultados favoráveis em relação à alteração de cor, dureza Shore A e resistência à tração para sua aplicação clínica em prótese bucomaxilofacial. A associação da pigmentação intrínseca, por meio de pó de maquiagem com opacificador, protegeu o silicone da alteração de cor e promoveu alterações aceitáveis nas propriedades mecânicas dos materiais. Todos os processos de envelhecimento promoveram alterações nas propriedades dos materiais. / The aim of this study was to propose the use of a new silicone (Bio-Skin - BS) for maxillofacial prosthesis. Color change, Shore A hardness, tensile strength, surface characteristics (SEM) and chemical composition (EDS) were analyzed, regarding different pigmentation and aging methods. The MDX4-4210 silicone was used as parameter of comparison. Specimens (120 circular and 160 dumbbell-shaped) were obtained for each material, from metal cutting molds, which were divided into 4 groups: IP - intrinsic pigmentation (makeup powder); OP - opacifier (barium sulfate, BaSO4); IPO - IP + OP association; WP - without adding IP or OP. Then, the specimens were randomly divided into 3 subgroups to aging by exposure to natural light (NL, n = 10), ultraviolet light (UV, n = 10) and without light (C, n = 10). The experimental period was 12 months. The color change was observed with spectrocolorimeter and CIE L*a*b* system. For hardness we used a Shore A durometer and the analysis of tensile strength was performed in a universal testing machine. The quantitative response variables were measured immediately after obtaining the specimens and after the experimental period. The surface analysis was performed by scanning electron microscopy (SEM) and the chemical composition of silicones, by energy dispersive spectroscopy (EDS). Data were submitted to ANOVA and Tukey\'s test (p <0.05). SEM and EDS results were presented in pictures and graphics. There was interaction between all factors (p <0.05) and both materials varied depending on the pigmentation and aging methods. For color change, the experimental silicone (BS) showed the lowest color variations. Analyzing the silicones due to the pigmentation, the MDX showed higher variation with the WP and OP specimens aged in natural light and UV light. For BS, there was significant change in the color of the WP and OP specimens only after aging for NL. The two materials presented an increase in hardness front of all conditions, and the BS silicone showed the greatest variation. The experimental silicone showed superior tensile strength to MDX in all situations. The MDX was not affected in tensile strength by any pigmentation or aging, except for the group pigmented with makeup powder and aged by UV, where there was an increase of resistance. As to BS silicone, the highest tensile strength values were found for the IP and IPO in all age groups. It can be considered that the experimental material showed favorable results regarding color change, Shore A hardness and tensile strength for clinical use in maxillofacial prosthesis. The association of intrinsic pigmentation through makeup powder and opacifier, protected silicone of color change and promoted acceptable changes in mechanical properties of the materials. All the aging processes promoted changes in material properties.

Les nanocomposites présentent des propriétés uniques dont l'origine est sujette à débat. Dans ce travail, nous cherchons à déterminer quel est l'impact de la morphologie de la charge et de son état de distribution sur les propriétés des matériaux. Pour cela, nous avons étendu un modèle théorique que nous résolvons numériquement.Nous avons étudié l'effet de la distribution des charges dans la matrice. Nous montrons qu'un état de distribution fortement hétérogène conduit à un renforcement plus important qui s'étend dans une plus large gamme de températures, mais augmente aussi la dissipation d'énergie. Ensuite, nous étudions l'effet de la structure des charges. Des particules parfaitement sphériques sont comparées à des agrégats fractals plus ou moins finement définis. Nous montrons que des objets finement définis peuvent s'imbriquer au sein de la matrice et conduisent à une augmentation du renfort et de la dissipation dans ces matériaux.Puis, nous étudions la réponse de nos systèmes lorsqu'ils sont soumis à une première élongation de forte amplitude. Nous montrons alors qu'un système hétérogène se plastifie localement progressivement au cours de la déformation alors qu'un système homogène présente une plastification catastrophique généralisée à partir d'une déformation critique. Enfin dans une dernière partie nous évaluons la possibilité d'étendre le modèle afin de simuler l'endommagement des nanocomposites. Nous introduisons pour cela un critère rupture local afin de prendre en compte l'endommagement du polymère entre les charges. Nous étudions ensuite comment se comportent les matériaux simulés en faisant varier la morphologie de la charge, son état de distribution et son taux.Ce travail constitue la première étude systématique de l'effet de la morphologie et de la distribution des charges sur les propriétés mécaniques des nanocomposites. Nous montrons que ces paramètres peu contrôlés sont pourtant des paramètres clés et peuvent servir à optimiser les propriétés d’usage d'un nanocomposite / Nano-filled elastomer composites are used in a very broad range of applications such as tires, damping materials and impact modifiers. The addition of nanoscale rigid particles in a polymer matrix induces nonlinear effects that are not yet fully understood far above the glass transition temperature of the pure matrix. A model of the reinforcement of nanocomposites based on the reduced mobility of the polymer confined between two spherical filler particles has been developed over the last ten years. In order to study the influence of the filler shape, structure, size, and dispersion state, we have extended the model were the morphology of the fillers is defined explicitly as spherical particles aggregated in the polymer matrix. The model is then solved by mesoscale numerical simulation in order to describe the mechanical properties of the nanocomposite. We study the mechanical response of nanocomposite filled with aggregates of different shapes and distribution state to deformations of various amplitudes in the reinforcement regime. We show that the mechanical behavior of nanocomposites strongly depends on the filler morphology and we propose that stress-relaxation mechanisms in the material are related to the disorder (particle size, aggregation number, distribution state) in the filler population. In a second part of this work, we study the mechanical response at larger amplitude in both a non-destructive and destructive regime. For that matter, the model has been extended in order to account for damaging of the polymer between filler particles.Our model opens the path for the development of systems with tailored properties by adjusting the fillers morphology and distribution.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho foram preparados nanocompósitos de elastômeros termoplásticos à base de PP/EPDM/argila organofílica. Foram utilizados como agentes interfaciais polipropileno e terpolímero de etileno-propileno-dieno ambos modificados com grupos anidrido maleico, PP-MA e EPDM-MA, respectivamente. Dois tipos de argila organofílica, que se diferenciam pela estrutura química do surfactante e conseqüentemente pela estabilidade térmica, foram empregados como carga inorgânica. Os nanocompósitos foram preparados pela técnica de intercalação por fusão em câmara interna de mistura e a incorporação da argila foi feita pela adição de masterbatches previamente preparados. Foram investigadas as propriedades de tração, reométricas e ainda a morfologia (cristalinidade e estrutura obtida) dos nanocompósitos a fim de estabelecer a influência do tipo e quantidade de argila organofílica e agente interfacial. Os resultados mostraram que a adição de agente interfacial melhorou a dispersão da argila organofílica na matriz de PP/EPDM, particularmente o PP-MA. Foram obtidos nanocompósitos com estruturas mistas intercaladas e esfoliadas, que resultaram em maiores valores de módulo de elasticidade e manutenção dos valores de deformação. As propriedades reométricas confirmaram o maior grau de dispersão da argila organofílica em nanocompósitos contendo PP-MA. Teores crescentes de argila reduziram a cristalinidade dos nanocompósitos, os quais quando reprocessados, mantiveram as características inerentes ao TPE de origem. Por fim, a estrutura do surfactante presente / In this work it was prepared nanocomposites based in PP/EPDM thermoplastic elastomer and organoclay. Maleinized polypropylene and ethylene-propylene-diene rubber, PP-MA and EPDM-MA, respectively, were employed as interfacial agents. Also two kinds of organoclays, differing about surfactant chemical structure and as consequence thermal stability, were investigated as inorganic filler. Nanocomposites were prepared by melt intercalation in an internal chamber mix and organoclay was incorporated by masterbatches addition, which ones were previously made. It was investigated the influence of amount and kind of organoclay and interfacial agent on tensile properties, rheology and morphology (crystallinity and structure type) of nanocomposites obtained. The results showed that interfacial agents addition promoted a better dispersion degree of organoclay platelets in PP/EPDM matrix, mainly PP-MA. Nanocomposites with both intercalated and exfoliated structures were obtained. These exhibited higher Young modulus and kept their elongation values. The better dispersion degree of clay platelets in nanocomposites containing PP-MA was confirmed by rheology measurements. Increasing amounts of organoclay lowered the crystallinity degree of nanocomposites but the reprocessability was maintained similar to that of pure TPE. Finally, the chemical structure of surfactants did not change the intercalation/exfoliation process due to the similarity of organoclay basal spacing and moderated TPE processing temperature.

This dissertation demonstrates the design of reversibly self-morphing novel liquid crystalline elastomer (LCE) antennas that can dynamically change electromagnetic performance in response to temperature. This change in performance can be achieved by programming the shape change of stimuli-responsive (i.e., temperature-responsive) LCEs, and using these materials as substrates for reconfigurable antennas. Existing reconfigurable antennas rely on external circuitry such as Micro-Electro-Mechanical-Systems (MEMS) switches, pin diodes, and shape memory alloys (SMAs) to reconfigure their performance. Antennas using MEMS or diodes exhibit low efficiency due to the losses from these components. Also, antennas based on SMAs can change their performance only once as SMAs response to the stimuli and is not reversible. Flexible electronics are capable of morphing from one shape to another using various techniques, such as liquid metals, hydrogels, and shape memory polymers. LCE antennas can reconfigure their electromagnetic performance, (e.g., frequency of operation, polarization, and radiation pattern) and enable passive (i.e., battery-less) temperature sensing and monitoring applications, such as passive radio frequency identification device (RFID) sensing tags. Limited previous work has been performed on shape-changing antenna structures based on LCEs. To date, self-morphing flexible electronics, including antennas, which rely on stimuli-responsive LCEs that reversibly change shape in response to temperature changes, have not been previously explored. Here, LCE antennas will be studied and developed. Also, the metallization of LCEs with different metal conductors and their fabrication process, by either electron beam (E-Beam) evaporation or optical gluing of the metal film will be observed. The LCE material can have a significant impact on sensing applications due to its reversible actuation that can enable a sensor to work repeatedly. This interdisciplinary research (material polymer science and electrical engineering) is expected to contribute to the development of morphing electronics, including sensors, passive antennas, arrays, and frequency selective surfaces (FSS).