<p>This Dissertation aims at establishing an integrated framework of multimodal experiments and multiphysics theory to extend the understanding of the mechanics in electrochemically active materials using organic mixed ionic-electronic conductors (OMIECs) as a model system. </p> <p>OMIECs allow the transport of both ions and electrons, which is accompanied by the (electronic, micro-) structural reorganization. The electronic structural change in OMIECs induces transforms in the electrical conductivity and optical absorbance. The change in molecular packing invites the size change and evolution of mechanical properties. The multiphysics processes render OMIECs a fascinating platform for understanding the multi-physics coupling and advancing organic electrochemical devices. </p> <p>Despite significant progress, there are urgent needs in the experimental techniques and the subsequent mechanical characterization, theoretical understanding of the multiphysics processes, and mechanics-informed design principles for high-performance devices. Specifically, (i) an accurate and straightforward experimental method is in need to better understand the mechanical behaviors and kinetics such as swelling and softening of OMIECs upon electrochemical redox reactions; (ii) a theoretical framework is missing that describes the rich coupled multiphysics processes such as large deformation, charge and mass transport, electrostatics, and phase evolution in OMIECs; (iii) the rational design of the materials and structures based on mechanics principles are required for mechanically reliable, high-performance organic electrochemical devices.</p> <p>In this Dissertation, the mechanics of OMIECs are studied systematically. The basics of OMIECs, knowledge gaps, and the outline are introduced in Chapter 1. The in-situ environmental nanoindentation apparatus and the associating characterization techniques are presented in Chapter 2. In Chapter 3, a theoretical mechanics model is presented that elucidates the interfacial mechanical degradation of thin-film electrodes and outlines the design principles for mechanically reliable electrodes. In Chapter 4, the electrochemical doping kinetics and its stress dependency on conductive polymers are studied via a designed moving front device. Chapter 5 presents a thermodynamically consistent continuum theory of two-phase OMIECs undergoing large deformation, charge and mass transport, electrostatics, and phase separation, which forms the theoretical foundation for such conductive polymer systems. The conclusion and perspectives on future work are presented in Chapter 6. </p>

<p>  </p> <p>The investigation of laser-matter interactions has gained interest over the years due to the importance of these interactions in materials synthesis, diagnostics, electronics, and photonics. In-situ transmission electron microscopy (TEM) techniques are invaluable for real-time monitoring of dynamic processes in these systems at the nanoscale. In this work, the effect of pulsed laser heating on the reactions of energetic materials, plasmonic structures, and multilayer thin films has been studied by utilizing ultrafast transmission electron microscopy (UTEM) techniques. Heat transfer and electric field calculations have been carried out to compare and support the experimental findings. </p> <p>The photothermal reaction of an aluminum-fluoropolymer composite is studied to show the effect of pulsed laser heating on reactions of reactive materials. An aluminum nanoparticle - THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) sample is subjected to rapid heating and cooling cycles by employing the integrated laser system of an UTEM. TEM images and real-time movies (30 frame/s) are acquired to reveal the changes during the reaction. Heat transfer simulations proved that the temperature of the sample was high enough to trigger the decomposition of THV and start its reaction with Al nanoparticles. Electron diffraction patterns revealed that the reaction product was the rare and metastable η-phase aluminum fluoride (AlF3). The experimental and theoretical results showed that rapid pulsed laser heating and subsequent cooling of a nanoscale sample influences the phases that can form and be utilized to investigate other systems.</p> <p>Pulsed laser-assisted merging and alloying of noble metals are also studied to explore the fabrication of beaded gold-silver nanowires with a variety of morphology and composition. In-situ laser heating of plasmonic silver nanowire (Ag NW) - gold nanoparticle (Au NP) couples are performed inside an UTEM, and direct visualization of the evolution process gives insights into the formation mechanism. Experimental results show that silver melts at the surface to bridge the nanometer-sized gap between the NP and the NW, forming a cup-like morphology underneath the Au NP via capillary action. Progressive laser irradiation leads to wetting of the Au NP and the formation of a valley in the Ag NW around the NP, which flattens gradually by partial embedding of the NP. Inter-diffusion of Au into Ag and vice versa sets in at this stage, leading to depletion of Au from the Au-rich NP region. Prolonged irradiation and heating lead to gradual inter-mixing of Au-Ag, forming a beaded Au-doped Ag nanowire with homogeneous composition. Such a step-by-step understanding of the merging and alloying process has implications in nanowelding, which holds a future in designing efficient, transparent conductors and printed electronics. Numerical simulations are performed to calculate the electromagnetic enhancement at the interface of adjacent NPs and NWs and provide information on heat generation rates in NP-NW couples at the early stages of the nanowelding process. </p> <p>In the third chapter, laser-induced irreversible dynamics in electron beam sensitive organic energetic crystals and ultrathin multilayer films are studied by single-shot UTEM imaging. After various sample preparation methods are developed and compared for the well-controlled synthesis of nanoscale ammonium perchlorate samples on TEM grids, decomposition dynamics of ammonium perchlorate crystals are captured via single-shot imaging. The experimental data showed that the sublimation and decomposition are visible ~30 ns after the sample excitation laser in crystals smaller than 5 µm. Dependency of decomposition to crystal porosity and thickness is also observed with crack formation in some cases. In the following section, pulsed-laser irradiation is utilized to realize deformation in thin multilayer films under high temperatures, and triggered dynamic processes are investigated through single-shot imaging. Laser-assisted periodic wrinkle formation is demonstrated on SiN membranes coated with Ti/Ni bilayers. The resulting structures showed periodic wrinkling of the SiN membrane and corrugated surface formation on both sides of the film. Overall, the dissertation highlights the potential of ultrafast transmission electron microscopy in discovering fundamental processes related to, but not limited to, reactive materials, plasmonic nanomaterials, and ultrathin multilayer films. </p>

Les zones côtières sont des milieux privilégiés pour l’ostréiculture. L’espèce la plus cultivée au monde est l’huître creuse Crassostrea gigas, qui a été introduite dans de nombreux pays à des fins d’exploitation et qui, lorsqu’elle trouve des conditions climatiques favorables dans son nouveau milieu, se développe naturellement, en constituant des récifs. Dans le Bassin d’Arcachon, l’huître existe ainsi sous deux formes, cultivée et sauvage. La forme récifale est une structure tridimensionnelle complexe (huîtres agglomérées, au contact du sédiment, plusieurs classes d’âge présentes), alors que les huîtres cultivées sont placées en sur-élévation dans des poches ostréicoles (spécimens isolés, classe d’âge unique). L’effet respectif de ces deux configurations a été étudié selon trois approches : (1) comparaison de la dynamique des deux types de population d’huîtres (croissance, reproduction, composition biochimique), (2) effet de l’activité alimentaire sur les proies accessibles dans le milieu et les flux particulaires associés, et (3) effets des huîtres sur le sédiment et les communautés benthiques. Les deux années d’échantillonnage ont été marquées par un retard de la ponte (année 1) et un défaut de croissance (année 2) des huîtres, qui ont été rapprochées d’un déficit thermique en période estivale (année 1) et d’une disponibilité alimentaire plus faible au printemps (année 2) ; les cycles de reproduction sont apparus en léger décalage entre huîtres cultivées et sauvages. Une expérimentation in situ en tunnels benthiques à trois périodes de l’année a permis de quantifier les flux de matière et la consommation de nutriments et d’espèces planctoniques par les deux populations d’huître durant un cycle de marée. Le sédiment à proximité des huîtres est enrichi en particules fines et en matière organique, par suite de modifications locales de l’hydrodynamisme et de la production de fèces par les huîtres. Il en résulte une modification de la structure des peuplements de l’endofaune benthique. Les récifs d’huîtres sauvages constituent un nouvel habitat de substrat dur dans le Bassin d’Arcachon où n’existent naturellement que des habitats sédimentaires ; ils supportent une épifaune à fortes biomasse et diversité, qui accroît la biodiversité locale. / Coastal areas are favourable environments for oyster farming. The most commonly farmed species in the world is the cupped oyster Crassostrea gigas, which was introduced in many countries for aquaculture purposes. When it finds suitable climatic conditions in its new environment, the species develops naturally, thereby creating oyster reefs. In Arcachon Bay (SW France), the cupped oyster develops as both farmed and feral populations. Oyster reefs are complex tridimensional structures (agglomerated oysters, in contact with the sediment, populations with many any classes), while farmed oysters are cultivated off-bottom in plastic bags (isolated oysters, populations with a single age class). The respective effects of these two oyster configurations were studied according to three research axes: (1) a comparison of the dynamics of farmed and wild oyster populations, in terms of growth, reproduction, and biochemical composition; (2) the effect of oyster feeding on accessible preys and the associated particulate fluxes; and (3) the effects of oysters on the sediment and benthic communities. The two years of study were characterized by a delay in the spawning periods (year 1) and an unusually low growth rate (year 2) in oysters, which were related to low summer water temperatures (year 1) and a low food availability in spring (year 2); reproduction cycles also appeared slightly shifted between farmed and wild oysters. An in situ experiment with benthic tunnels at three periods of the year was designed to quantify the flux of matter and the consumption of nutrients and planktonic species by the two oyster populations during a tidal cycle. Sediment in the vicinity of oysters contained more fine particles and organic matter, due to changes in local hydrodynamism and oyster production of faeces. These sedimentary changes modified the structure of benthic infaunal assemblages. Oyster reefs form a new habitat of hard substrate in Arcachon Bay, where only sedimentary habitats naturally occur; they have an epifauna with high biomass and diversity, that increases the local biodiversity.

The aim of this thesis was to investigate the impact of a direct oxygen injection as a potential remediation strategy for contaminated aquifers on a bench scale. The mass transfer between a multi-component trapped gas phase and a mobile water phase was studied. Column experiments with dynamically compressed sediments and a direct gas injection of pure oxygen gas were performed. In addition, a new developed kinetic multi-component model was used to describe the experiments. The amount of gas that could be captured in the pore space during direct oxygen injection and the time needed for a complete dissolution of the trapped gas phase were determined. Varying influences of different gases already dissolved in the mobile water phase on the dissolution process of a trapped oxygen gas phase were described for different flow regimes and confirmed by the model results. Finally, on the basis of the experimental and model results obtained in this thesis, predictions for an application of a direct oxygen injection in the field were discussed.

Les interactions entre organismes ont des conséquences majeures sur la composition des communautés et le fonctionnement des écosystèmes. En écologie l'étude des interactions négatives, telles que la prédation et la compétition, a largement dominé la littérature. Des travaux récents ont souligné l’importance des interactions positives dans la nature, telles que la facilitation, mais ces interactions restent malgré tout peu intégrées dans les théories contemporaines en écologie. Cette thèse s’inscrit dans cette démarche et aborde deux questions centrales : (i) Comment la facilitation indirecte (via la protection contre le pâturage) affecte-t-elle la structure fonctionnelle (caractéristiques des distributions de traits) des communautés de plantes ? (ii) L'effet net des interactions facilitatrice-bénéficiaire identifiées à l’échelle d’une paire d’espèces restent-elles valides en présence d’une communauté entière d'espèces bénéficiaires potentielles ? Deux expérimentations in situ dans des environnements contrastés ont été mises en place : l’exclusion du pâturage dans des tourbières tropicales alpines et une transplantation de communautés de plantules sous des plantes adultes en milieu méditerranéen semi-aride. Nous avons montré que la facilitation indirecte affectait les caractéristiques du filtre environnemental, la dominance des espèces et la différenciation de niche au sein de la communauté. Nos travaux suggèrent également que la composition des communautés de plantules modifie les interactions adultes-plantules, remettant ainsi en cause la possibilité d’extrapolation des résultats entre paires d'individus à l’échelle de la communauté. / Interactions between organisms are key drivers of community composition and ecosystem functioning. Ecology has a long history of studies on negative interactions, such as predation and competition. Recent studies have highlighted the importance of positive interactions, such as facilitation in nature. The integration of these interactions into modern ecological theory has nonetheless lagged behind. This thesis aims at contributing to this research effort and addresses two core questions : (i) How does indirect facilitation (through protection against grazing) affect the functional structure (characteristics of trait distributions) of plant communities? (ii) Does the net effect of the interactions between a species pair (benefactor-beneficiary) remain valid in the presence of several beneficiary species at community level? We set up two insitu experiments in contrasted environments: a grazing exclusion experiment in tropical alpine peatlands and a transplantation experiment of sapling communities beneath adult plants in a mediterranean environment. Our results showed that indirect facilitation affects the characteristics of the environmental filter, species dominance and niche differentiation in the community. Our results also suggested that the composition of sapling communities modifies adult-sapling interactions, thereby questioning the possibility of extrapolating results from pairs of individuals to the community scale.

Transparent trä biokompositer (TW) är en ny attraktiv klass av biokomposit. De är uppbyggda av delignifierat trä som impregnerats med en polymer med matchande brytningsindexet.  TW kan skräddarsys för inom ett brett spektrum av funktionella, optiska och mekaniska egenskaper. Eftersom de är biobaserade ses de dessutom som ett möjligt material som kan ersätta andra, mer miljöpåverkande material, inom olika sektorer, däribland byggnadsindustrin. Till skillnad från de funktionella egenskaperna har det mekaniska beteendet hos dessa biokompositer dock inte undersökts särskilt ingående. Syftet med denna avhandling är därför att utöka den nuvarande kunskapen om det mekaniska beteendet av dessa material genom att använda två olika mekanisk karakterisering metoder av TW och vanligt trä som referensmaterial. TW framställdes genom impregnering av delignifierade björkfaner med PMMA. Den mekaniska karakteriseringen utfördes med hjälp av olika metoder. Elastiska modulen och böjhållfastheten i tvärriktningen studerades med hjälp av fyrpunktsböjningprov. Resultaten visade en förbättring för båda egenskaperna jämfört med vanligt björkträ. Brottet vinkelrätt mot fibern (TR-systemet) undersöktes genom att utföra in situ fyrpunktsböjningstester på prover med en kant-spricka i ett svepelektronmikroskop för att observera hur sprickorna fortplantar sig i den komplexa mikrostrukturen. En anmärkningsvärd förbättring (cirka 175 procent) av brottsstyrkan konstaterades jämfört med vanligt trä. Dessutom användes DIC-teknik (digital image correlation) på fyrpunktsböjningstesterna, med kant-spricka, för att studera spänningsfältet under spricktillväxten, särskilt bildandet av brottprocesszonen (FPZ) runt sprickspetsen. Därefter föreslogs en ekvation som beskriver kohesionslagen för båda materialen baserat på experimentella observationer som i slutändan kan användas för sprickmekaniska simuleringar. Slutligen visades kort hur man kan använda de uppmätta mekaniska egenskaperna hos den nya TW för materialval för tekniska tillämpningar. / Transparent wood (TW) biocomposites are a new attractive class of materials. They are based on a delignified wood template impregnated by a refractive index-matching polymer.  TWs can be tailored in order to show a wide range of functional, optical, and mechanical properties. Moreover, being biobased, they are seen as a possible key material to replace more environmentally impactful materials in various sectors including the construction industry. However, unlike the functional properties, the mechanical behaviour of this class of materials has been poorly investigated. Therefore, in this thesis, the aim was to extend the current knowledge about the mechanical response of these materials by using a two-step mechanical characterization on TW and native wood as reference material. The analysed TW biocomposite was prepared by impregnation of delignified birch veneers by PMMA. The mechanical characterization was carried out using different techniques. The Young’s modulus and the flexural strength along the transverse direction were studied by four-point bending tests. The results showed an improvement for both properties compared to native birch wood. The fracture perpendicular to the grain (TR system) was investigated by performing in situ single-edge-notched four-point bending tests onto a scanning electron microscope to observe how the cracks propagate in this complex microstructure. A remarkable improvement (about 175 percent) in fracture toughness was found compared to the native wood. Furthermore, the in situ single-edge-notched four-point bending test was also applied, together with the digital image correlation (DIC) technique, to study the strain field during the crack growth, specifically the formation of the fracture process zone (FPZ) around the crack tip. Then, an equation describing the cohesive law was proposed for both materials based on experimental observations that can be ultimately used for fracture mechanics simulations. Finally, it was briefly shown how to make use of the measured mechanical properties of the novel TW for material selection for engineering applications.