Colloidal nanoparticles (NPs) can assemble into a large variety of superlattices, going from amorphous glassy assemblies towards periodic and aperiodic structures, which eventually display collective physical properties. However, our understanding of the different experimental parameters affecting the final assembled structure is still incomplete which prevents a predictive approach towards the design of NP superlattices. The aim of this thesis is to control the two-dimensional self-assembly of NPs at the liquid/air interface from the evaporation of a NP dispersion on a liquid surface. The first chapter reviews the state of art on NP synthesis, colloidal interactions, self-assembly, quasicrystals, aperiodic superlattices and collective properties. In the second chapter, we discuss the synthesis of well-defined hydrophobic spherical gold NPs and their self-assembly. Many different structures were observed: hexagonal close-packed monolayers, Moiré patterns, fused NPs. Then, we investigated the self-assembly of binary systems composed of spherical or cubic NPs by varying several experimental parameters. In Chapter four, we focus on the synthesis and self-assembly of triangular CeF3 nanoplatelets (NPLs). Using time-resolved in situ SAXS/WAXS, we investigated their growth mechanism and evidence a nucleation-induced lamellar self-assembly process. In the last chapter, we report the synthesis and self-assembly of square CdSe NPLs. Finally, we investigated the binary self-assembly of triangular and square NPLs with the same edge length to reproduce the pattern of quasicrystalline structures. Our study helps to establish guiding principles for film formation and structure tuning, a first step towards more complex superlattices to design new nanomaterials. We also open a route toward the understanding of NPL formation and bring insights that can be extended to other systems and will facilitate the rational design of colloidal NP assemblies.
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Disciplines