Publication : Films Langmuir-Blodgett composés de copolymères di-blocs et de nanoparticules métalliques
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2017
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Cette thèse de doctorat étudie l’auto-assemblage de copolymères di-blocs et de nanoparticules métalliques à l’interface air-eau. Les nanoparticules métalliques peuvent interagir fortement avec la lumière grâce à l’oscillation collective des électrons de conduction. Ce phénomène, qu’on appelle le plasmon de surface localisé, offre d’importantes perspectives dans l’élaboration de matériaux optiques. Cependant, la force et la fréquence du plasmon de surface varient significativement en fonction de plusieurs paramètres dont l’arrangement des nanoparticules. Les copolymères à blocs, quant à eux, ont la capacité de former des domaines de morphologies définies à la surface de l’eau et représentent une voie simple pour organiser les nanoparticules en deux dimensions. Avec la technique Langmuir-Blodgett, il a été possible de former des monocouches composites de nanoparticules et de copolymères, et de les transférer sur des substrats solides. Les films composites Langmuir-Blodgett ont été caractérisés par microscopie à force atomique et par microscopie électronique en transmission. Plusieurs auto-assemblages, incluant des agrégats, des systèmes cœur-satellites, des cercles et des lignes de nanoparticules ont été observés. Les caractéristiques structurales de ces assemblages peuvent être ajustées avec précision en modifiant l’organisation des copolymères et la longueur des ligands thioalcanes à la surface des nanoparticules. De plus, une procédure de recroissance in situ a été développée pour augmenter la taille des nanoparticules incorporées sans altérer l’ordre des monocouches. Les propriétés optiques des auto-assemblages ont ensuite été étudiées expérimentalement et comparées à des simulations théoriques par l’approximation aux dipôles discrets. Une attention particulière a été portée aux nanocercles qui sont des structures hautement symétriques et compliquées à obtenir avec d’autres méthodes. Enfin, la thèse se termine par une série d’expériences préliminaires destinées à évaluer l’utilité de ce type de monocouches pour des applications de détection.
The present Ph. D. thesis treats the investigation of the self-assembly of block copolymers and metallic nanoparticles at the air-water interface. Metallic nanoparticles interact strongly with light because of the collective oscillation of the conduction electrons. This phenomenon is called the localized surface plasmon resonance and offer significant promise in the development of optical materials. However, the strength and frequency of the surface plasmon depend on several parameters, including details of the arrangement of the nanoparticles. As block copolymers can form nanodomains at the surface of water, they represent a simple way to organize nanoparticles in two dimensions. With the help of the Langmuir-Blodgett technique, it has been possible to form composite monolayers composed of nanoparticles and block copolymers, which are transferable on solid substrate. The Langmuir-Blodgett composite films have been characterized both by atomic force microscopy and transmission electron microscopy. Several self-assemblies, including aggregates, core-satellite structures, nanorings, and particle lines have been observed. The structural characteristics of these assemblies can be tuned precisely by modifying the copolymer organization and the capping ligand length at the nanoparticle surface. In addition, an in situ regrowth procedure has been developed to increase the size of the incorporated nanoparticles without losing the order of the monolayers. Then, optical properties of the self-assemblies have been investigated experimentally and compared to theoretical calculations by the discrete dipole approximation. Particular attention has been paid to the nanoring structures, which are highly symmetrical and complicated to obtain with other fabrication procedures. Finally, the thesis presents a series of preliminary experiments intended to assess the usefulness of the monolayers for sensing applications.
The present Ph. D. thesis treats the investigation of the self-assembly of block copolymers and metallic nanoparticles at the air-water interface. Metallic nanoparticles interact strongly with light because of the collective oscillation of the conduction electrons. This phenomenon is called the localized surface plasmon resonance and offer significant promise in the development of optical materials. However, the strength and frequency of the surface plasmon depend on several parameters, including details of the arrangement of the nanoparticles. As block copolymers can form nanodomains at the surface of water, they represent a simple way to organize nanoparticles in two dimensions. With the help of the Langmuir-Blodgett technique, it has been possible to form composite monolayers composed of nanoparticles and block copolymers, which are transferable on solid substrate. The Langmuir-Blodgett composite films have been characterized both by atomic force microscopy and transmission electron microscopy. Several self-assemblies, including aggregates, core-satellite structures, nanorings, and particle lines have been observed. The structural characteristics of these assemblies can be tuned precisely by modifying the copolymer organization and the capping ligand length at the nanoparticle surface. In addition, an in situ regrowth procedure has been developed to increase the size of the incorporated nanoparticles without losing the order of the monolayers. Then, optical properties of the self-assemblies have been investigated experimentally and compared to theoretical calculations by the discrete dipole approximation. Particular attention has been paid to the nanoring structures, which are highly symmetrical and complicated to obtain with other fabrication procedures. Finally, the thesis presents a series of preliminary experiments intended to assess the usefulness of the monolayers for sensing applications.
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thèse de doctorat