With respect to the principles of biomineralization, it is of interest to study the crystallization of calcium oxalates under various experimental conditions. Calcium oxalates play decisive roles as biominerals in plants and as pathological “urinary/kidney stones” in vertebrates. Calcium oxalate exists in three different hydration states; calcium oxalate monohydrate (COM, monoclinic, a = 6.290(1)Å, b = 14.583(1)Å, c = 10.116(1)Å, β = 109.46°, P21/c), calcium oxalate dihydrate (COD, tetragonal, a = b = 12.371(3)Å, c = 7.357(2)Å, α = β = γ = 90°, I4/m) and calcium oxalate trihydrate (COT, triclinic, a = 6.11(1)Å, b = 7.167(2)Å, c = 8.457(2)Å, α = 76.5(2)°, β = 70.35(2)°, γ = 70.62(2)°, P ). Monoclinic COM and tetragonal COD are the most common phyto-crystals and the main constituents of kidney and urinary stones. The occurrence of calcium oxalates in plants represents a useful biogenesis (protection against herbivores) unlike the devastating occurrence in renal tubules. Therefore, biomineralization can be physiological or pathological. A systematic investigation of the morphological evolution of calcium oxalates in the presence of organic components is essential for understanding the mechanism of “pathological biomineralization”. In order to understand the pathological biomineralization of uroliths, it is necessary grow calcium oxalates comparable in morphology under similar growth conditions. The formation of calcium oxalate stones within a gelatinous state of proteins, polysaccharides, lipids and other biomacromolecules under a flow of supersaturated urine supports the fact that an “organic” gel model can simulate the process of urinary stone formation under in vitro conditions. Furthermore, synthetic polymers with precisely known functions and solution behaviours are better choices to understand the interaction of acidic proteins with calcium oxalates. Therefore, as a first step to unravel the complex pathology of uro/nephro lithiasis, we started to examine the structure and morphology of calcium oxalates crystallized in the presence of organic additives such as the sodium salt of polyacrylic acid (PAA) as well as agar gel. The influence of initial calcium oxalate concentration, pH and concentration of the additives on the formation of hydration states of calcium oxalates have been investigated along with the stated general methods. Apart from the three hydrated forms, calcium oxalate exists also in the anhydrous form (COA). Although three modifications of COA (α, β and γ) are reported in the literatures, the crystal structures and phase transformations were controversially discussed. We have been able to reveal the crystal structure of the β-modification of the anhydrous calcium oxalate by a combination of atomistic simulations and Rietveld refinements on the basis of powder X-ray diffraction pattern. β-COA belongs to the monoclinic system with unit cell parameters, a = 6.1644(3)Å, b = 7.3623(2)Å, c = 9.5371(5)Å, β = 90.24(2)°, P2/m (No. 10). The dehydration of COM was mimicked in silico to receive an initial model of the crystal structure of anhydrous calcium oxalate. This general approach may also be accessible for other decomposition processes ending up with crystalline powders of unknown crystal structure. No evidence for transformations from or to the α- or γ- modifications was found during our investigations. The growth pattern of COD crystals precipitated from aqueous solutions in the presence of PAA is clearly dependent on the concentration of PAA. By increasing the concentration of PAA, the shape of COD has been found to change from tetragonal bi-pyramids with dominant (101) pyramidal faces to tetragonal prisms with dominant (100) prism faces and finally to dumbbells. At still higher PAA concentrations, the morphology is reverted back to rod-like tetragonal prisms. Apart from these experiments, the interaction of PAA with (100) and (101) crystal faces of COD was explored with the aid of atomistic simulations. The simulation confirmed that during the development of the aggregates, strong interactions of PAA with the (100) faces take over control of morphologies. Our investigations show that the inner architecture of all the morphological varieties of COD was found to be dominated by an inner “core” consisting of thin elongated crystallites together with incorporated PAA and an outer “shell” formed as a consequence of secondary nucleation processes. We propose that for all types of COD aggregates, relative proportion of calcium oxalate and PAA dictates the shape and formation of nanometer sized crystallites which then aggregate and align to form the core. Such cores enriched with PAA may act as the sites for secondary nucleation events of calcium oxalate crystallites which then cover the core like a shell. In vitro experimental models for the growth of calcium oxalates can give valuable information on the growth and aggregation of urinary stones. Therefore, the “double diffusion technique” in agar gel matrix has been used for the biomimetic growth of calcium oxalate (COM) stones. A great variety of morphological forms of COM are produced in agar gel matrices (2 wt.-% agar gel of pH 8.5) ranging from platy crystallites to dumbbells and spherulites. The COM dumbbells and spherulites are assumed to be formed by the aggregation of smaller crystallites as a consequence of increased supersaturation inside the gel. Moreover, an increase of the pH value of the agar gel has been found to suppress the growth of COM and favours the growth of COD. The morphology of COD crystals grown in 2 wt.-% agar gel of pH 11.5 includes tetragonal prisms and dumbbells. The system calcium oxalate/ PAA/ H2O is a suitable model system for the investigation of principles of biomineral growth (shape development) in general. Our results demonstrate that the double diffusion technique in agar gel is a convenient route to grow calcium oxalate aggregates showing close resemblance to biogenic calculi and to study their ontogeny.

Doubly cross-linked gels were fabricated based on tetra-poly(ethylene glycol) (Tetra-PEG) by shear strain. These are gels with two network structures present in the same polymeric network. The second network structure is introduced by applying a mechanical field to the first natural network structure. These doubly cross-linked gels indicated a negative energy elasticity supporting earlier findings where the energy elasticity was found significantly negative for Tetra-PEG gel. Acquired results indicate implications for past research on the elasticity of polymer gels where the energy contribution was approximated to zero. Obtained results also indicated that the modulus of rigidity for the doubly cross-linked gels is constant regardless of applied shear strain during fabrication. This would indicate that the same second network structure is formed for the interval of 25-800% applied shear strain. The residual strain for the fabricated gels can be well-described using an exponential fitting of the apparent shear modulus of the first network structure and an expression derived from the two-network theory and classic rubber theory. These theories also seem to predict the experimental residual strains for lower strain regions (<100%) quite well. However for larger strain regions (>100%) non-linear effects seem to affect the results causing a deviation. A slight increased modulus of rigidity was noted for the doubly cross-linked gels compared to the regular Tetra-PEG gel. However as the reproducibility of the concluded measurements could not be confirmed during this thesis the results are not conclusive and only indicate the conclusions mentioned above.

We live in a time of many challenges. The ‘Great Acceleration’ (Steffen et al., 2015) is a trend that can be observed in numerous fields in our world: be it the development of CO2 emissions, the land use or the enormous amount of produced plastics accompanied by massive environmental pollution. This ‘phenomenon’ is obviously directly linked to the way we live and how our society works. To meet these developments, we need to move away from the big, prone concepts that got us here in the first place, and instead build on a variety of dynamic and changing solutions.

Les hydrogels sont des matériaux aux propriétés modulables dont la dégradation peut être contrôlée. Du fait de leur biocompatibilité, ils peuvent être utilisés afin de protéger les médicaments labiles et ainsi favoriser l’administration de traitements médicaux, d’où l’intérêt croissant de développer ces matériaux. Depuis quelques années, ils font l’objet de nombreuses recherches, que ce soit en ingénierie tissulaire, détection de mouvement, régénération de tissus ou pour le relargage de médicaments. Ce projet de thèse porte sur la formation d’hydrogels à base d’α-cyclodextrine et de polyéthylène glycol 20K ainsi que sur l’étude de leur capacité de relargage de principes actifs. Ces composés ont la capacité de former des complexes d’inclusion, créant ainsi un collier de perle, appelés pseudopolyrotaxane. Ensuite, ils seront modifiés pour créer des hydrogels de polyrotaxanes grâce à l’ajout de groupement bloquants. Finalement, nous formerons des hydrogels à point de réticulations glissant après avoir relié deux polyrotaxanes par leur macrocycle. À l’aide d’études rhéologiques, nous avons montré une amélioration des propriétés mécaniques des hydrogels proportionnelle à l’apport de liaisons chimique. Les groupements bloquants permettent d’éviter la désinclusion tandis que les réticulations apportent un effet poulie, les rendant exceptionnellement élastique. Ces hypothèses sont validées par les études structurales. Et nos hydrogels se sont révélés non toxiques pour les cellules humaines et ces résultats confirment leur biocompatibilité. Les hydrogels de pseudopolyrotaxanes sont les plus écologiques et les plus appropriés pour une application locale cutanée. Les hydrogels de polyrotaxanes, plus stables, peuvent être utilisés pour des applications locales prolongées ou par injection. Cependant, nos hydrogels de polyrotaxanes réticulés devront être modifiés afin de permettre un relargage contrôlé, car leur extrême stabilité pourrait entraver leur dégradation lors d'une injection sous-cutanée malgré leurs propriétés mécaniques exceptionnelles. / Hydrogels are materials with tunable properties whose degradation can be controlled. Because of their biocompatibility, they can be used to protect labile drugs and thus facilitate the administration of medical treatments, hence the growing interest in developing these materials. In recent years, they have been the subject of numerous studies, whether in tissue engineering, motion sensing, tissue regeneration or drug delivery. This project focuses on the formation of hydrogels based on α-cyclodextrin and polyethylene glycol 20K and the study of their drug release capacity. These compounds can form inclusion complexes, forming a pearl necklace called pseudopolyrotaxane. They will then be modified to form polyrotaxane hydrogels by adding blocking groups. Finally, we will form hydrogels with sliding cross-linking points after linking two polyrotaxanes through their macrocycle. Through rheological studies, we have demonstrated an improvement in the mechanical properties of the hydrogels proportional to the introduction of chemical bonds. Blocking groups prevent desorption, while cross-linking provides a pulley effect, making them exceptionally elastic. These hypotheses are supported by structural studies. Our hydrogels have been shown to be non-toxic to human cells, confirming their biocompatibility. Pseudopolyrotaxane hydrogels are the most environmentally friendly and suitable for local cutaneous application. Polyrotaxane hydrogels are more stable and can be used for prolonged local applications or by injection. However, our cross-linked polyrotaxane hydrogels will need to be modified to allow controlled release, as their extreme stability could hinder their degradation during subcutaneous injection, despite their exceptional mechanical properties.

This dissertation aims to develop, characterize, and fundamentally understand a new class of materials termed "molecular ionic composites" (MICs). MICs show promise as next-generation solid electrolytes for batteries. MICs form when mixing a rigid polyanion with purely ionic fluids, and they behave mechanically as a solid but contain a high density of ions that move nearly as in a neat liquid. Specifically, prototypical MICs are based on solutions of the rigid-rod polyelectrolyte poly(2,2'-disulfonyl-4,4'-benzideneterephthalamide) (PBDT), which forms a double helix, combined with imidazolium-based ionic liquids (ILs). The IL comprises 75-97 wt% of the final solid, even though the Young's modulus can reach ~ 2 GPa at 80 wt% IL. We propose that these properties are driven by a biphasic internal structure in MICs corresponding to IL-rich "puddles" (an interconnected liquid phase) and PBDT-IL associated "bundles" where IL ions form the collective electrostatic associations that cause the MICs to be a solid. Through this dissertation I will discuss a wide variety of MICs that have been created through the use of two different formation processes, the "ingot" method and the "solvent casting" method, which allow for the use of many different ionic fluid sources to further tune MIC properties. The following chapters build to the fundamental knowledge and our current understanding of the wide variety of materials that can be created from PBDT and IL. / Doctor of Philosophy / Battery electrolytes, biosensors, and hydrogels all depend on new materials for next-generation applications. For these new materials to be used characterization on the interactions, morphological restrictions, and/or what unique internal structures used to generate their properties must be performed. Through This analysis using common polymeric characterization techniques these materials can be further optimized. This dissertation highlights a new class of materials termed "molecular ionic composites" (MICs) which are formed from a rigid double helical polymer, poly(2,2'-disulfonyl-4,4'-benzideneterephthalamide) (PBDT), and fluids composed entirely of ions, including ionic liquids (ILs). These composite systems feature a unique combination of properties including high thermal stability, mechanical stability, and excellent ionic conductivity, all of which are highly tunable through the amount of PBDT incorporated or the fluid ion types. Chapters 3, 4, 5, and 6 present fundamental investigations of MICs to determine how tunable they are, the processes by which they form, and the various ways we can fabricate them. Chapter 7 describes the creation of another impressive material formed from PBDT-low-polymer-content hydrogels. These studies are intended to provide deeper understanding of the behaviors of these unique materials and how they may be used in the future.

Tesis por compendio / [ES] El objetivo de esta tesis doctoral ha sido el diseño y caracterización estructural de estructuras tipo gel basadas de polisacáridos extraídos de biomasa acuática con interés para aplicaciones relacionadas con la alimentación. Las propiedades de los polisacáridos extraídos de algas y plantas acuáticas son adecuadas para producir diferentes estructuras tipo gel basadas en la formación de redes reticuladas, como hidrogeles, aerogeles y emulsion-gels. En la primera parte de esta tesis se investigaron los diferentes mecanismos de gelificación de polisacáridos sulfatados, así como los parámetros que afectan a la estructura y las propiedades funcionales de los hidrogeles obtenidos. En base a los resultados, se evaluó la potencial aplicación de los hidrogeles y aerogeles de agar y k-carragenato para encapsular una proteína alimentaria modelo como la caseína, explorando así el efecto protector contra la hidrólisis enzimática tras digestiones gastrointestinales simuladas. En la segunda parte de esta tesis, se desarrollaron estructuras de aerogeles mediante la valorización de una fuente de biomasa residual infrautilizada, como es el Arundo donax. Con esta biomasa se generaron fracciones celulósicas con diferentes grados de purificación y extractos bioactivos solubles en agua, que posteriormente se utilizaron para producir aerogeles bioactivos híbridos. La estructura altamente porosa y la elevada capacidad de sorción de los aerogeles los convierten en excelentes candidatos para la sustitución de las almohadillas absorbentes para mantener la calidad de los productos cárnicos envasados. Los emulsion-gels son reconocidos por su gran potencial como ingredientes funcionales en la industria alimentaria como modificadores de textura y como sustitutos de grasas sólidas. Además, pueden utilizarse como vehículo para la liberación controlada de compuestos bioactivos liposolubles. Así, en la última parte de esta tesis, se investigó la naturaleza de las interacciones entre los componentes en las formulaciones de emulsion-gels basadas en polisacáridos y se relacionó con su estructura y comportamiento mecánico y reológico. Después de estudiar el mecanismo de gelificación de los emulsion-gels de carragenato, estos sistemas se adaptaron y utilizaron para dos diferentes aplicaciones relevantes para los sectores de alimentación y biomedicina. En primer lugar, se produjeron y evaluaron estructuras gelificadas a partir de emulsion-gels de agar y k-carragenato y aerogeles cargados de aceite como encapsulantes de un bioactivo lipofílico como la curcumina. Los resultados mostraron que el tipo de polisacárido y el estado físico de las redes del gel tenían un impacto en la estructura de los productos de la digestión. Por otro lado, se evaluó el potencial de los emulsion-gels basados en polisacáridos sulfatados (k-carragenato y agar) para la producción de un material capaz de simular tejido graso. Los resultados evidencian que los emulsions-gels de agar son adecuadas para producir materiales que simulan las propiedades dieléctricas para imitar tejidos de bajo y alto contenido en agua. / [CA] L'objectiu d'aquesta tesi doctoral ha sigut, el disseny i caracterització estructural d'estructures tipus gel, basades en polisacàrids extrets de biomassa aquàtica amb interès per a aplicacions relacionades amb l'alimentació. Les propietats dels polisacàrids extrets d'algues i plantes aquàtiques, són adequades per a produir diferents estructures tipus gel basades en la formació de xarxes reticulades, com a hidrogels, aerogels i emulsió-gels. En la primera part d'aquesta tesi es van investigar els diferents mecanismes de gelificació de polisacàrids sulfatats, així com els paràmetres que afecten l'estructura i les propietats funcionals dels hidrogels obtinguts. Sobre la base dels resultats, es va avaluar la potencial aplicació dels hidrogels i aerogels d'agar i k-carraguenina per a encapsular una proteïna alimentària model com la caseïna, explorant així l'efecte protector contra la hidròlisi enzimàtica després de digestions gastrointestinals simulades. A la segona part d'aquesta tesi, es van desenvolupar estructures d' aerogels mitjançant la valorització d'una font de biomassa residual infrautilitzada, com és el Arundo donax. Amb aquesta biomassa es van generar fraccions cel·lulòsiques amb diferents graus de purificació i extractes bioactius solubles en aigua, que posteriorment es van utilitzar per a produir aerogels bioactius híbrids. L'estructura altament porosa i l'elevada capacitat de sorció dels aerogels els converteixen en excel·lents candidats per a la substitució dels coixinets absorbents per a mantenir la qualitat dels productes carnis envasats. Els emulsió-gels són reconeguts pel seu gran potencial com a ingredients funcionals en la indústria alimentària com a modificadors de textura i com a substituts de greixos sòlids. A més, poden utilitzar-se com a vehicle per a l'alliberament controlat de compostos bioactius liposolubles. Així, a l'última part d'aquesta tesi, es va investigar la naturalesa de les interaccions entre els components dins les formulacions d' emulsió-gels basades en polisacàrids i es va relacionar amb la seua estructura i comportament mecànic i reològic. Després d'estudiar el mecanisme de gelificació dels emulsió-gels de carraguenina, aquests sistemes es van adaptar i es van utilitzar per a dues aplicacions diferents, rellevants per als sectors de l' alimentació i la biomedicina. En primer lloc, es van produir i van avaluar estructures gelificades a partir de emulsió-gels d'agar i k-carraguenina i aerogels carregats d'oli com a encapsulants d'un bioactiu lipofílic com la curcumina. Els resultats van mostrar que el tipus de polisacàrid i l'estat físic de les xarxes del gel tenien un impacte en l'estructura dels productes de la digestió. D'altra banda, es va avaluar el potencial dels emulsió-gels basats en polisacàrids sulfatats (k-carraguenina i agar) per a la producció d'un material capaç de simular teixit gras. Els resultats evidencien que els emulsió-gels d'agar són adequats per a produir materials que simulen les propietats dielèctriques podentimitar teixits de baix i alt contingut en aigua. / [EN] The aim of this doctoral thesis was to design and characterize the structure of gel-like structures based on polysaccharides extracted from aquatic biomass, with interest for food-related applications. The properties of polysaccharides extracted from seaweeds and aquatic plants make them suitable to produce a range of gel-like structures based on the formation of interconnected networks, such as hydrogels, aerogels and emulsion-gels. In the first part of this thesis, the different gelation mechanism of sulphated polysaccharides and the parameters affecting the structure and functional properties of the obtained hydrogels were investigated. Based on the results, the potential application of agar and k-carrageenan hydrogels and aerogels to encapsulate a model food protein such as casein was evaluated, thus exploring the protective effect against the enzymatic hydrolysis upon simulated gastrointestinal digestions. In the second part of this thesis, aerogel structures were developed by valorising an underutilized waste biomass source such as Arundo donax. This biomass was used to generate cellulosic fractions with different purification degrees and water-soluble bioactive extracts, which were subsequently used to produce hybrid bioactive aerogels. The highly porous structure and high sorption capacity of aerogels make them excellent candidates for the replacement of absorbent pads to maintain the quality of packaged meat products. Emulsion-gels are recognized for their great potential as functional ingredients in the food industry to modify texture and for solid fat replacement. Moreover, they can be used as a delivery vehicle for the controlled release of fat-soluble bioactive compounds. Thus, in the last part, the nature of interactions between the components in polysaccharide-based emulsion-gel formulations was investigated and related to their structure and mechanical and rheological behavior. After studying the gelation mechanism of carrageenan emulsion-gels, these systems were adapted and used for two different applications relevant to the food and biomedicine sectors. Firstly, oil-filled gel-like structures from agar and k-carrageenan emulsion-gels and oil-filled aerogels were produced and evaluated as carriers of a lipophilic bioactive such as curcumin. The results showed that the polysaccharide type and the physical state of the gel network had an impact on the structure of the digestion products. On the other hand, the potential of emulsion-gels based on sulphated polysaccharides (k-carrageenan and agar) for the production of tissue mimicking phantoms was evaluated. The results evidence that the agar emulsion-gels are suitable to produce materials simulating the dielectric properties to mimic low- and high-water content tissues. / Synchrotron experiments were performed at NCD beamline at ALBA Synchrotron with the collaboration of ALBA staff (2018022638 project). This work was financially supported by the grant RTI2018-094268-B-C22 (MCIU/AEI/FEDER, UE). Part of this work was supported by the COST Action ES1408 European network for algal-bioproducts (EUALGAE). Cynthia Fontes-Candia is recipient of a pre-doctoral grant from CONACYT (MEX/Ref. 306680). The projects RTI2018-094268-B-C22 and RTI2018-094408-J-I00 were funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. This work has also received financial support from project PID2019-107663RB-I00 from the Spanish Ministry of Science and Innovation (MICINN). Cynthia Fontes-Candia is recipient of a pre-doctoral grant from CONACYT (MEX/Ref. 306680). Marta Martinez-Sanz is recipient of a Juan de la Cierva (IJCI-2015-23389) contract from the Spanish Ministry of Economy, Industry and Competitiveness. / Fontes Candia, C. (2022). Development and Characterization of Gel-Like Structures from Aquatic Biomass for Food Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/181564 / Compendio

Among the myraid energy storage technologies, polymer electrolytes have been widely employed in diverse applications such as fuel cell membranes, battery separators, mechanical actuators, reverse-osmosis membranes and solar cells. The polymer electrolytes used for these applications usually require a combination of properties, including anisotropic orientation, tunable modulus, high ionic conductivity, light weight, high thermal stability and low cost. These critical properties have motivated researchers to find next-generation polymer electrolytes, for example ion gels. This dissertation aims to develop and characterize a new class of ion gel electrolytes based on ionic liquids and a rigid-rod polyelectrolyte. The rigid-rod polyelectrolyte poly (2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) is a water-miscible system and forms a liquid crystal phase above a critical concentration. The diverse properties and broad applications of this rigid-rod polyelectrolyte may originate from the double helical conformation of PBDT molecular chains. We primarily develop an ionic liquid-based polymer gel electrolyte that possesses the following exceptional combination of properties: transport anisotropy up to 3.5×, high ionic conductivity (up to 8 mS cm⁻¹), widely tunable modulus (0.03 – 3 GPa) and high thermal stability (up to 300°C). This unique platform that combines ionic liquid and polyelectrolyte is essential to develop more advanced materials for broader applications. After we obtain the ion gels, we then mainly focus on modifying and then applying them in Li-metal batteries. As a next generation of Li batteries, the Li-metal battery offers higher energy capacity compared to the current Li-ion battery, thus satisfying our requirements in developing longer-lasting batteries for portable devices and even electric vehicles. However, Li dendrite growth on the Li metal anode has limited the pratical application of Li-metal batteries. This unexpected Li dendrite growth can be suppressed by developing polymer separators with high modulus (~ Gpa), while maintaining enough ionic conductivity (~ 1 mS/cm). Here, we describe an advanced solid-state electrolyte based on a sulfonated aramid rigid-rod polymer, an ionic liquid (IL), and a lithium salt, showing promise to make a breakthrough. This unique fabrication platform can be a milestone in discovering next-generation electrolyte materials. / Ph. D. / Among the myraid energy storage technologies, polymer-based electrolytes have been widely employed in diverse applications such as fuel cell membranes, battery electrolytes, “artificial muscle” mechanical actuators, reverse-osmosis membranes and solar cells. The materials used for each of these applications usually require a specific combination of properties, which include anisotropic orientation, tunable mechanical stiffness (modulus), high ionic conductivity, light weight, high thermal stability and low cost. These critical properties have motivated researchers to find next-generation polymer-based electrolytes, for example “ion gels” that consist of a polymer combined with ionic liquids or salts. This thesis describes development of an ion gel that possesses the following exceptional combination of properties: high ionic conductivity (up to 8 mS cm^-1), widely tunable modulus (0.03 ‒ 3 GPa), ion transport anisotropy up to 3.5×, and high thermal stability (up to 300°C). Thus, this unprecedented material shows liquid-like ion motions inside a matrix with solid-like stiffness, and in a material that can withstand extreme temperatures and will not burn. After obtaining these ion gels, we are then mainly focusing on modifying them for application in safe and high density Li-metal batteries. As a next generation of Li batteries, the Li-metal battery offers higher energy capacity compared to the current Liion battery, thus satisfying our requirements in developing longer-lasting batteries for portable devices and even electric vehicles. However, Li dendrite growth on the Li metal anode has limited the pratical application of Li-metal batteries. This unexpected Li dendrite growth can be supressed by developing polymer electrolytes with high modulus (~ GPa), while maintaining sufficient ionic conductivity (~ 1 mS/cm) for efficient battery operation. In short, this thesis describes an advanced solid-state electrolyte based on a kevlar-like (sulfonated aramid) rigid-rod polymer, an ionic liquid (IL), and a lithium salt, showing promise to make a breakthrough and enable practical Li-metal batteries. Furthermore, the unique fabrication platform for these ion gels represents a new paradigm for discovering next-generation electrolyte materials for a wide variety of applications.

The development of bio-resorbable implant materials is rapidly going on. Sterilization of those materials is inevitable to assure the hygienic requirements for critical medical devices according to the medical device directive (MDD, 93/42/EG). Biopolymer-containing biomaterials are often highly sensitive towards classical sterilization procedures like steam, ethylene oxide treatment or gamma irradiation. Supercritical CO2 (scCO2) treatment is a promising strategy for the terminal sterilization of sensitive biomaterials at low temperature. In combination with low amounts of additives scCO2 treatment effectively inactivates microorganisms including bacterial spores. We established a scCO2 sterilization procedure under addition of 0.25% water, 0.15% hydrogen peroxide and 0.5% acetic anhydride. The procedure was successfully tested for the inactivation of a wide panel of microorganisms including endospores of different bacterial species, vegetative cells of gram positive and negative bacteria including mycobacteria, fungi including yeast, and bacteriophages. For robust testing of the sterilization effect with regard to later application of implant materials sterilization all microorganisms were embedded in alginate/agarose cylinders that were used as Process Challenge Devices (PCD). These PCD served as surrogate models for bioresorbable 3D scaffolds. Furthermore, the impact of scCO2 sterilization on mechanical properties of polysaccharide-based hydrogels and collagen-based scaffolds was analyzed. The procedure was shown to be less compromising on mechanical and rheological properties compared to established low-temperature sterilization methods like gamma irradiation and ethylene oxide exposure as well as conventional steam sterilization. Cytocompatibility of alginate gels and scaffolds from mineralized collagen was compared after sterilization with ethylene oxide, gamma irradiation, steam sterilization and scCO2 treatment. Human mesenchymal stem cell viability and proliferation were not compromised by scCO2 treatment of these materials and scaffolds. We conclude that scCO2 sterilization under addition of water, hydrogen peroxide and acetic anhydride is a very effective, gentle, non-cytotoxic and thus a promising alternative sterilization method especially for biomaterials.

La formation de cristaux dans la phase dispersée d'une émulsion huile-dans-eau fait apparaître des irrégularités ou aspérités aux interfaces pouvant entraîner des modifications rhéologiques spectaculaires comme le passage d'un état fluide à un état solide. Nous montrons que la gélification des émulsions par voie thermique peut être attribuée à deux mécanismes : la coalescence partielle, qui permet grâce aux cristaux interfaciaux deformer des liens irréversibles entre gouttes, et le «jamming » qui est un phénomène de blocage dû aux aspérités empêchant le mouvement relatif des surfaces au contact. Sur des systèmes modèles, nous établissons que les mécanismes et les cinétiques de gélification sont contrôlés par la proportion d'huile cristallisée, le diamètre moyen des gouttes et la composition de l'interface. Nous montrons en particulier que la coalescence partielle peut être décrite comme un processus de percolation nécessitant des contacts de type « solide contre liquide » entre les gouttes. Nous montrons ensuite que la mise en écoulement des émulsions ou des gels peut conduire à deux situations limites : la séparation macroscopique des phases (ou barattage) ou bien la persistance d'un gel de plus faible connectivité. Nous étudions l'influence des paramètres qui sont à l'origine de cette évolution topologique. La variété des états accessibles rend ces matériaux très attractifs pour les secteurs de la cosmétique et l'agroalimentaire.

Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network. The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering. The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error. KEYWORDS:Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling. / <p>QC 20161026</p>