The increasing production and usage of engineered nanoparticles has raised concerns about potential ecological and human exposures and the risks these novel materials may pose. Nanoparticles are often manufactured with an organic macromolecular coating, and they will attain further coatings of adsorbed natural organic matter (NOM) in the environment. The overall objective of this thesis is to improve our ability to quantify the effects of adsorbed coatings on nanoparticle fate in the environment. The physicochemical properties of the coating or the adsorbing macromolecule are expected to strongly mediate the surface interactions, and hence the environmental fate, of coated nanoparticles. To this end, this research focuses on assessing a coating characterization method and applying extensive characterization of NOM coatings to enable the development of correlations to predict nanoparticle deposition onto model environmental surfaces and aggregation. The first objective is to assess the applicability of a soft particle electrokinetic modeling approach to characterize adsorbed layer thickness, which contributes to repulsive steric forces that will affect nanoparticle deposition. A statistical analysis determined that high uncertainty in fitted layer thicknesses will limit this approach to thin, low-charged coatings (for which it may be advantageous to typical sizing methods such as dynamic light scattering). Application of this method in experimental studies further confirmed the model limitations in estimating layer thicknesses and the inability of this measurement (and other commonly measured properties) to fully explain nanoparticle deposition behavior. These results demonstrated the need for improved detail and accuracy in coating characterization. The second objective is to correlate the properties of NOM to its effects on gold nanoparticle aggregation, with particular focus on the role of heterogeneity or polydispersity of the NOM molecular weight. Multiple types of NOM collected from representative water bodies and soils were used, both in whole and separated into molecular weight (MW) fractions, and characterized for chemical composition and MW distribution. While average MW of the NOM provided good correlation with aggregation rate, the highest MW components were found to contribute disproportionately in stabilizing nanoparticles against aggregation, highlighting the importance of measuring and accounting for high MW components to explain nanoparticle aggregation. However, an outlier from the MW trend was identified, emphasizing the need for additional characterization (e.g. of reduced sulfur content or the conformation of the adsorbed NOM) to fully explain the effects of NOM on nanoparticle aggregation. Altogether, this research provides novel knowledge that will guide future application of characterization methods to predict attachment processes for coated nanoparticles in the environment.

The application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA) which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analysed using the change in the Gibbs free energy computed by Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The Gibbs free energy was highest for PAA coated CNPs by 250 kg/mole indicating the most stable coating. The free energy for PAA 100 kg/mole coated CNPs is 85% lower than the PAA250 coated CNPs. This significant difference is caused by the strong adsorption of PAA100 on CNPs. Catalytic activity of PAA-CNPs is accessed by the catalase enzymatic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. Apart from PAA coating the catalase activity is also affected by the structure of the coating layer.

Cette thèse porte sur l'étude de milieux granulaires constitués de particules molles. Elle s'appuie d'une part sur la méthode de corrélation d'images numériques (DIC) et d'autre part sur des simulations associant la méthode des éléments finis (FEM) et la méthode de Dynamique des Contacts (CD) permettant de tenir compte de la déformabilité élevée des particules et des interactions entre particules. Pour une large gamme de matériaux complexes (élastique, plastique et mousse solide), l'étude préliminaire de particules uniques comprimées radicalement valide la technique de DIC pour les mesures des champs de déformation, et pour la détermination de l'énergie de déformation pour des matériaux élastiques. Des grandeurs macroscopiques et micro-structurales tels que la compacité, la coordinence, l'énergie élastique, la densité de la probabilité de force de contact ainsi que de la densité d'énergie sont mesurées, et comparées entre les résultats numériques et expérimentaux en particulier dans le régime où les déformations des particules sont d'amplitudes finies. L'accord quantitatif entre ces approches permet de valider à la fois la méthode expérimentale pour l'étude de milieux granulaires à particules déformables, et d'autre part l'approche numérique. Forts de ces résultats, nous avons mené une étude numérique de la compression uniaxiale d'un assemblage de cylindres Néo-Hookéens. L'effet du frottement sur les paramètres macroscopiques et mico-structuraux est déterminé, y compris lorsque la compacité du système est proche de 100% / This thesis deals with the study of granular media composed of soft particles. It relies on the one hand on the method of Digital Image Correlation(DIC) and on the other hand, on simulations coupling the Finite Element Method and the Contact Dynamics method, taking into account the high deformability of particles and interactions between particles. For a wide range of complex materials (elastic, plastic and solid foam), the preliminary study of radially compressed single particles validates the DIC technique for strain field measurements, and for the determination of the strain energy for elastic materials. Macroscopic and micro-structural quantities such as packing fraction, coordination, elastic energy, probability density of the contact force as well as strain energy density, are measured and compared between the numerical and experimental results in particular in the regime where the deformations of the particles are large. The quantitative agreement between these approaches makes it possible to validate both the experimental method for the study of granular media with deformable particles, and the numerical approach. Based on these results, we conducted a numerical study of the uniaxial compression of a Neo-Hookean cylinder assembly. The effect of friction on the macroscopic and mico-structural parameters is determined, even when the packing fraction of the system is close to 100%.

Les microgels sont des particules colloïdales de polymère réticulé gonflées par un solvant. Déformables et poreuses, elles peuvent changer d’état de gonflement lors de l’application d’un stimulus. Ce travail de thèse a pour but de développer de nouveaux concepts tirant profit des propriétés stimulables et de la déformabilité intrinsèque des microgels tout en approfondissant les connaissances sur le comportement de ces objets en solution et aux interfaces. Les microgels de poly(N-alkylacrylamide) sont utilisés comme modèles. Dans un premier temps, notre travail a porté sur l’étude d’un nouveau type de microgels électrochimiluminescents grâce à l’incorporation d’un complexe métallique de ruthénium dans la matrice polymère. A la transition de phase, ces microgels présentent une exaltation de l’intensité ECL jusqu’à 2 ordres de grandeur, en lien avec la distance entre les sites redox. Le concept est ensuite transposé à des microgels sensibles aux saccharides et à des systèmes comportant deux luminophores, un donneur ECL et un accepteur d’énergie pouvant donner lieu à un transfert d’énergie par résonance. La deuxième partie de la thèse est consacrée à l’adsorption de microgels à une interface liquide-liquide plane, en vue de mieux comprendre l’origine de la stabilité des émulsions stabilisées par ce genre d’objets. De façon analogue aux protéines flexibles, les microgels changent de conformation à l’interface, passant d’un état étendu à un état comprimé, à l’origine de variations de l’élasticité interfaciale. Les microgels ainsi adsorbés sont fonctionnalisés de façon régiosélective dans l’eau et permettent de produire des microgels non symétriques, dits Janus, susceptibles de s’auto-assembler. / Microgels are colloidal particles made of cross-linked polymer swollen by a solvent. Soft and porous, they can adapt their swelling degree in response to a stimulus. The main objective of this work is to develop new concepts taking advantage of microgels’ stimuli-responsive properties and intrinsicsoftness while deepening understanding of their properties in solution and at interfaces. Poly(Nalkylacrylamide) microgels are used as a model. Initially our work focused on the study of a new type of electrochemiluminescent (ECL) microgels thanks to the incorporation of a ruthenium complex in the polymer matrix. At the volume phase transition, these microgels exhibit an amplification of the ECL intensity up to 2 orders of magnitude, related to the decrease of the distance between redox sites. This concept is then transposed to saccharides-sensitive microgels and systems bearing two luminophores, an ECL donor and an energy acceptor in order to give rise to resonance energy transfer. The second part of this manuscript is devoted to adsorption of microgels at a planar liquid-liquid interface, to improve knowledge on the origin of the stability of emulsions stabilized by such objects. Such as flexible proteins, microgels can change their conformation at the interface, from an extended to a compressed state, causing variation in the interfacial elasticity. When microgels are adsorbed they can also be functionalized regioselectively in water to produce non-symmetrical microgels, called Janus, able to self-assemble.