Cornwell, Mabel Alice; (2024) Studies towards the optimisation of the continuous flow production of nanomaterials by development of fine-tuned reproducible and robust particle synthesis techniques. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In recent years, extensive development has made nanotechnology a compelling and progressive area of scientific interest. The variety of nanoparticles under study exhibit diverse physical and chemical characteristics, offering potential applications across many fields. Bottom-up synthesis approaches, which begin at the atomic level, allow for tighter control over product uniformity. However, current nanoparticle production methods are typically conducted in batch systems, leading to inevitable product variability. Flow synthesis enhances reaction control, reduces costs, and increases safety; however, it faces challenges like fouling and reproducibility due to the complexity of nanomaterial synthesis. This thesis describes the development of flow synthesis methods that achieve controlled, reproducible, high-quality nanomaterial while eliminating fouling. A continuous two-phase flow reactor design that effectively controls the size of gold nanoparticles while preventing fouling has been developed to produce gold citrate-capped quasi-spherical nanoparticles within the critical size range of 20-60 nm, important for biomedical and sensing applications. By tuning a one-step seeded-growth method, this reactor can continuously produce monodisperse gold nanoparticles in the desired size range. For a more universal application, antibiofouling techniques such as polymer brush surface modifications and slippery liquid-infused porous surfaces (SLIPS) were explored to prevent fouling in nanomaterial flow synthesis. This led to a general-use antifouling reactor, developed by the covalent attachment of (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichlorosilane molecules to the PTFE wall, followed by a coating of Krytox® oil. This multipurpose reactor was able to produce various metal-based nanoparticle species under varying reaction conditions without fouling when compared to an unmodified control reactor, as evidenced both visually and through nanoparticle product characterization. Finally, a continuous three-phase flow setup was developed to translate the extensively studied Brust-Schiffrin synthesis of gold nanoparticles from batch to flow, producing small, uniform thiol-capped gold nanoparticles in toluene. This method uses an aqueous phase for the introduction the reducing agent and a gas phase to capture evolving hydrogen.

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