Cangiano, Alessandro (2025) Design and physico-chemical characterisation of colloidal nanocrystals supramolecular structures. [Tesi di dottorato]

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Abstract

The rational design of novel materials with precisely controlled properties is a cornerstone of modern scientific research and technology. Among the most promising strategies for creating such materials, there is the “bottom-up” approach, wherein nanoscale building blocks are directed to self-assemble into larger, ordered supramolecular structures. This method holds the potential to generate metamaterials with emergent collective properties, such as unique optical, electronic, or catalytic functionalities, that are not present in the individual components or their disordered arrangements.1,2 Colloidal nanocrystals (NCs), with their tunable size, shape, and surface chemistry, represent exceptionally versatile building blocks for this purpose. 2 Despite significant progress, the ability to precisely control the self-assembly process to achieve specific, complex architecture remains a formidable challenge. The final structure of an NCs assembly is governed by a delicate and complex interplay of interparticle forces, which are highly sensitive to both the intrinsic properties of the NCs and the environmental conditions. A comprehensive understanding of how to manipulate these factors to drive the assembly towards desired outcomes is essential for moving beyond empirical trial-and-error and toward true rational design. This thesis aims to elucidate the fundamental principles governing the self-assembly of NCs into ordered supramolecular aggregates. The central hypothesis is that by systematically tuning key parameters, namely the ligand shell density of the NCs building blocks and the polarity of the solvent environment, it is possible to rationally direct the self-assembly process to achieve specific nanoscale architectures with tailored collective properties. To address this, this work undertakes a systematic investigation, starting from the synthesis of well-defined metallic nanoparticles (NCs) of Au, Ag, and Pt with distinct surface properties, and proceeding to explore their assembly into both single-component and complex binary supramolecular structures. The research presented in this thesis is structured as follows: Chapter 1 provides the fundamental theoretical background on NCs and the driving forces that govern their self-assembly. Chapter 2 details the synthesis and rigorous physico-chemical characterisation of the NCs building blocks, establishing their core properties and response to different solvent environments. Chapter 3 presents the core investigation into single-component self-assembly, demonstrating how ligand density and solvent polarity act as powerful tools to select the final supramolecular phase and its associated functional properties. Finally, Chapter 4 extends these design principles to binary systems, exploring how the co-assembly of plasmonic (Au) and semiconductor (CeO2) NCs can be controlled to create synergistic materials with enhanced optical functionalities, thus providing a direct link between structural design and emergent function.

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