Ce travail de thèse décrit l’alignement par pulvérisation de nanofils d'argent (AgNWs) aux interfaces solides sous la forme de films mono- et multicouches. Cette technique permet de contrôler la densité de nanofils dans le plan sur des zones macroscopiques avec des paramètres d'ordre nématique atteignant des valeurs > 0,90 dans les films monocouches. La répétition des cycles de dépôt en utilisant l’assemblage couche-par-couche produit des films multicouches dans lesquels par exemple des superstructures uniaxiales ou hélicoïdales peuvent être préparées en choisissant les directions de pulvérisation appropriées pour chaque monocouche individuelle. Les systèmes uniaxiaux sont des polariseurs fortement dépendant de la longueur d'onde (en raison de l'orthogonalité des plasmons transversaux et longitudinaux des AgNWs) et montrent une conductivité anisotrope dans le plan. Les systèmes hélicoïdaux montrent un dichroïsme circulaire très élevé qui peut être ajusté par exemple par le biais de la densité des AgNWs dans le plan ou de la distance entre les monocouches individuelles. Les mesures de la matrice Müller confirment que le dichroïsme circulaire observé découle de la superstructure hélicoïdale des multicouches à base d’AgNWs. / This thesis work describes the spray-alignment of silver nanowires (AgNWs) at solid interfaces in the form of mono- and multilayer films. The technique allows to control the in-plane density of nanowires over macroscopic areas with the best nematic order parameters reaching > 0.90 in monolayer films. Repeated deposition cycles using layer-by-layer assembly yield multilayer films in which for example uniaxial or helically twisted superstructures can be prepared by choosing appropriate spraying directions for each individual monolayer. Uniaxial systems are strong wavelength dependent polarizers (due to the orthogonality of the transversal and longitudinal plasmons of the AgNWs) and they show anisotropic in-plane conductivitiy. Helically twisted systems show very high circular dichroism which can be tuned for example through the in-plane density of AgNWs or through the distance between individual monolayers. Müller Matrix measurements confirm that the observed circular dichroism arises from the helically twisted superstructure of the AgNW multilayers.

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La cellulose étant l'un des biopolymères les plus abondants, elle est employée dans ce travail de thèse sous sa forme nano-fibrille (2 à 5nm de diamètre et plusieurs microns de long) pour préparer des nanomatériaux durables. Les microfibrilles de cellulose (MFC) chargées positivement ou négativement sont assemblées en couches minces dans ces nanomatériaux par la méthode « Layer by Layer » (LbL) par trempage, pulvérisation ou spin assisté. Les différences entre ces films LbL à base de MFC et les films LbL à base de polymères standards sont discutées brièvement et sont reliées à la forme nanofibrillaire de la cellulose. Les MFC réagissent comme des nano-objets anisotropes et rigides. Les films LbL de MFC sont ensuite intégrés à des membranes de séparation, entre la couche polymérique de séparation et le support poreux, pour améliorer le débit à travers ces membranes. Ces films minces sont également déposés sur des aérogels de cellulose pour améliorer la stabilité de ces aérogels en milieu aqueux. Dans les deux applications, les résultats était encouragent et montre une validation de principe. / Cellulose, one of the most abundant biopolymers, is used in this PhD work in its nanofibrillated form, 2-5 nm in diameter and microns long, to prepare sustainable nanomaterials. Both positively and negatively charged microfibrillated celluloses (MFC) are assembled in these nanomaterials using the versatile Layer by Layer (LbL) assembly methods: dipping, spray assisted-deposition and spin-assisted deposition. A brief comparison between the MFC based LbL assembled films and the standard polymeric LbL films is carried out. Thedifferences between the two species are related to the fibrillar form of cellulose. MFC behaves like rigid anisotropic nano-objects. MFC LbL assembled films are then integrated in separation membranes between active polymeric separation layers and a mechanically stable porous support to improve the flux through these membranes. MFC LbL assembled films are also coated on cellulosic aerogels to improve the wet stability of these aerogels. In both cases, results were encouraging and showed a proof of concept.

Ce travail de thèse a été consacré à l'élaboration d'un nouveau type de membranes de nanofiltration efficaces avec des propriétés améliorées (flux élevé et rétention élevée, et de bonnes propriétés mécaniques) en déposant un revêtement assemblé couche-par-couche (LbL) sur des supports poreux. Après avoir systématiquement étudié le mécanisme de croissance des films assemblés couche par couche des polyélectrolytes choisis et la relation entre les structures de ces films et les performances des membranes résultant, nous avons identifié avec succès les meilleures structures multicouches pour la construction de membranes de nanofiltration de référence avec des performances optimales. En outre, en prenant avantage de la technique LbL, nous avons introduit une couche de diffusion latérale assemblée soit de nanofibrilles de cellulose ou de nanotubes de carbone, qui permet d’augmenter le flux de 30% tout en conservant la même rétention par rapport à la membrane de référence. En plus, les films assemblés à base de chitosan et nanofibrils de cellulose ont montré une forte résistance à la traction allant jusqu’à 450 MPa et un module d’Young jusqu’à 50 GPa. / This thesis work was devoted to the development of a novel and efficient nanofiltration membrane with improved properties (high flux and high retention, good mechanical strength) by coating Layer-by-Layer (LbL) assembled films onto porous membrane support. After having systematically studied the growth mechanism of LbL-assembled films of chosen polyelectrolytes and the relationship between the structures of these films and the membrane performance of the resulting NF membranes, we successfully identified the best multilayer structures for constructing nanofiltration membranes (NF) of reference with optimal membrane performance. Furthermore, taking advantages of the LbL-assembly, we successfully introduced LbL-assembled lateral diffusion layer that is made of either cellulose nanofibrils or carbon nanotubes, which in turn led to membranes with 30% higher flux. In addition, the LbL-assembled films of chitosan and cellulose nanofibrils showed surprisingly strong tensile strength of up to 450 MPa and a high Young modulus of up to 50 GPa.

The understanding of self-assembly processes is important for fabrication of well-defined structures with new functionalities for applications in the area of biomedical sciences, material sciences and electronics. In this thesis, two types of self-assembly processes are described: (1) self-assembly of fullerene derivatives in water and (2) self-assembly on surfaces using layer-by-layer (LbL) approach. The various interactions and parameters involved in the self-assembly are detailed in the introductory chapter 1. The various internal parameters like molecular geometry, intramolecular and intermolecular forces that guides the self-assembly process of amphiphiles in water are discussed. The experimental procedures used in the present thesis for the fabrication of nanostructures via self-assembly approach are also described. In the later part of the chapter, the LbL technique for fabrication of thin films and microcapsules is reviewed where various interactions involved in the growth of LbL assembly are discussed. The effect of ionic strength and pH on the growth and property of LbL assemblies is elaborated. A brief discussion of the materials used in the thesis ‒ fullerene, bovine serum albumin (BSA) and nanocrystalline cellulose (NCC) is also provided The self-assembly behaviour of amphiphilic fullerene derivatives are described in chapter 2. Fullerene is anisotropically substituted with five polar hydroxyl groups using organo-copper reagent. The derivative can interact in water via the van der Waals and hydrophobic interactions of the fullerene moiety as well as the intermolecular hydrogen bonding among the hydroxyl groups and also with water. The penta-hydroxy fullerene derivative self-assembles in water as vesicular structures. The size of these vesicles can be varied by modifying the kinetics of self-assembly which was done by changing the rate of addition of non-solvent (water) to the solution of the fullerene derivative. In the second derivative, the hydroxyl groups are substituted with less polar methoxy groups. The penta-methoxy fullerene derivative cannot participate in inter-molecular hydrogen bonding formation unlike the penta-hydroxy derivative but there is possibility of hydrogen bond formation with water where oxygens on methoxy group can act as hydrogen bond acceptor. The penta-methoxy fullerene does not show any vesicle formation in water. The computational simulation studies were carried out on the two fullerene derivatives to understand the self-assembly behaviour of these two derivatives. Furthermore, the vesicle structures formed by the penta-hydroxy fullerene derivative are used for entrapment of hydrophobic polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and also hydrophilic dye, Rhodamine B. In both the cases, fluorescence quenching is observed due to electron transfer reaction with fullerene and hence these fullerene vesicles can be used to study the effect of confinement on electron transfer reactions and other chemical dynamics. The layer-by-layer self-assembly approach for the fabrication of biopolymeric thin films and microcapsules is discussed in the chapters 3 to 6. The biocompatible nanoparticles and nanofibers were used as the components of the assembly. In chapter 3, we have described fabrication of thin film of bovine serum albumin (BSA) nanoparticles via LbL approach using biopolymer chitosan as the complementary polymer. The driving force for the assembly growth of the assembly was the electrostatic and complementary hydrogen bond formation between the two components. The idea of incorporating nanoparticles in the thin film was that the nanoparticles can act as reservoirs for functional materials. The films were loaded with anticancer drug doxorubicin and show pH dependent release of the drug. The various interactions involved in the LbL assembly of BSA nanoparticles and polymers were investigated towards understanding the growth mechanism of the assembly in chapter 4. The understanding of the interactions involved in the assembly formation is important in order to modify the conditions of the assembly for enhancing the growth. It is inferred from the study reported in this chapter that not only the interaction of nanoparticles with polymers but also the inter-particle interactions are important factors in determining the growth of LbL assembly of nanoparticles/polymers. The growth of the assembly is enhanced on minimizing the inter-particle repulsions, which was achieved in case of BSA nanoparticles by modifying the pH of the assembly. We also utilized the LbL self-assembly approach for the delivery of lipophilic drugs. The lipophilic drugs are difficult to administer in the body due to their poor water solubility and hence show poor pharmacokinetic profile. The methods for incorporating hydrophobic drugs in LbL assembled thin films and microcapsules are described in chapters 5 and 6. In chapter 5, hydrophobic molecules binding property of albumin has been exploited for solubilisation of a water-insoluble molecule, pyrene (model drug) and hydrophobic drug, curcumin, by preparation of non-covalent conjugates with BSA. The interaction with BSA provided negative zeta potential to the previously uncharged molecules and hence they can be incorporated in the LbL assembled thin films and microcapsules using electrostatic as well as hydrogen bonding interaction with biopolymer, chitosan. The fabrication of protein encapsulated stable microcapsules with hydrophobic molecules incorporated in the shell of the microcapsules has also been demonstrated. The microcapsules were further capable of loading hydrophilic molecules like Rhodamine B. Thus, this approach can be employed for fabrication of multi-agent carrier for hydrophobic and hydrophilic drugs as well as therapeutic macromolecules. In chapter 6, we have incorporated nanocrystalline cellulose (NCC) LbL assembled thin films and microcapsules. The assembly formed was porous in nature due to the nano-fibrous morphology of NCC. The nanoassemblies can act as potential drug delivery carrier, which has been demonstrated by loading anticancer drug doxorubicin, and a lipophilic drug, curcumin. Doxorubicin hydrochloride, the salt form of the drug, doxorubicin, has good water solubility and hence can be postloaded in the assembly by diffusion from its aqueous solution. In the case of curcumin, which has limited solubility in water, a stable aqueous dispersion of the drug was prepared via noncovalent interaction with NCC prior to incorporation in the LbL assembly. The interaction of various other lipophilic drugs with NCC was analysed computationally.

Ma thèse a porté sur des complexes de polyélectrolytes en solution et en films LbL pour la transfection de cellules et le contrôle des interactions cellule-surface. Il est possible de doser un agent de transfection et de l'ADN plasmidique dans des films LbL en ajustant le nombre de couches. Les efficacités de transfection avec différentes lignées cellulaires ont été au moins aussi bonnes que celles rapportées dans la littérature, mais sont restées globalement faibles. Différents nanobags ont également été systématiquement testés menant à un protocole de transfection très efficace avec une faible cytotoxicité pour des fibroblastes humains qui sont difficiles à transfecter. Nous avons pu identifier les architectures LbL qui permettent de contrôler l'adhésion cellulaire même en présence de sérum. Cela nous a permis d'introduire une nouvelle technique pour le suivi in situ de la transfection par QCM-D en suivant la mobilité du cytosquelette qui sera poursuivie dans un futur projet. / My PhD work was focused on polyelectrolyte complexes in bulk and in LbL-films for cell transfection and for controlling cell-surface interactions. It is possible to dose transfection agent and plasmid DNA in LbL-films by adjusting the number of layers. Transfection efficiencies with different cell lines were at least as good as reported in the literature, but remained overall weak. Different nanobags were also tested systematically leading to a highly efficient transfection protocol with low cytotoxicity for human fibroblasts which are difficult to transfect. We were able to identify multilayer architectures that allow to control cell adhesion even in the presence of serum. This allowed us also to introduce a new technique for the in-situ monitoring of transfection by QCM-D through monitoring cytoskeleton mobility which will be further pursued in a future research project.