Nüesch, FrankOpris, Dorina MariaOwusu, Francis2023-03-202023-03-202023-03-20202310.5075/epfl-thesis-10244https://infoscience.epfl.ch/handle/20.500.14299/196259Recent advancements in miniature devices with higher computational capabilities and ultralow power consumption have accelerated the development of wearable sensors, actuators, and energy harvesters everywhere. The ultimate aim of such a technological revolution is to create an ecosystem of connected devices and transform physical objects into information sources. To achieve this, flexible materials with the versatility to be designed into complex architectures will be of relevance. Among the different energy transducing technologies, piezoelectricity has been earmarked as one of the leading routes due to its simple conversion mechanism, relatively high power density, and easy integration into various systems. However, conventional piezoelectric materials are limited in many applications due to their rigidity, high density, lack of machinability, inability to conform to delicate parts of systems and arbitrary interfaces. For this reason, there is an appreciable demand for developing new materials, which can sustain large mechanical deformation while retaining superb characteristics in their performance. This thesis systematically presents processing steps for preparing highly elastic piezoelectric materials solely from organic constituents. The approach combines selected organic reactions available in the synthesis toolbox and composite preparation technique. Novel polar amorphous polymers bearing different dipole moieties were synthesized, processed into nano-particles, and embedded as fillers in a polydimethylsiloxane (PDMS) matrix. To this end, we employed the power and versatility of ring-opening metathesis polymerization (ROMP) to synthesize polar amorphous polymers with high dielectric relaxation strength and glass transition temperature (Tg) significantly above room temperature. The collection of novel polymers was thoroughly characterized by NMR spectroscopy, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The dielectric behaviors were further investigated by broadband dielectric spectroscopy (BDS), and thermally stimulated depolarization current (TSDC) techniques. Structure-property relationships were established to evaluate the optimal material with promising properties to be used as a filler in the composite preparation. The polar amorphous polymer with optimal characteristics is then processed into particulate forms by the nanoprecipitation method. Sub-micrometer particles with sizes ranging from 90 nm to 2 µm could be obtained. Elastomeric composites were then prepared by impregnating different weight fractions of the filler particles into PDMS matrix. Following the successful processing of the blends into chemically cross-linked thin films, piezoelectric activity was induced by electric poling. The piezoelectric properties of the prepared elastic composites showed strong dependence on the filler weight fraction, particle size, stereo-regular configuration of the polar polymer particles, and the poling technique employed. A quasi-stable transverse piezoelectric coefficient (d31) of 37 pC N-1 could be recorded for the best-performing material poled by corona discharge. In addition, these piezoelectric materials could withstand large mechanical deformations (maximum strain at break up to 400%) as a peculiar advantage compared to the prevailable piezoelectric polymer and ceramic materials.enPolar amorphous polymersRing-opening metathesis polymerization (ROMP)PDMS matrixcomposite film processingcorona polingelastic electretsmolecular dipolespiezoelectric elastomerspiezoelectric polymerstransverse piezoelectric charge coefficientthesis::doctoral thesis