Thesis

Multimodal characterisation of silicates : combining fluorescence imaging, spectroscopy, and molecular simulations

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Awarding institution
  • University of Strathclyde
Date of award
  • 2025
Thesis identifier
  • T17513
Person Identifier (Local)
  • 202187267
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Department, School or Faculty
Abstract
  • Silica-based nanomaterials are central to catalysis, coatings, and sustainable technologies, yet their rapid and reliable characterisation remains challenging. Traditional methods such as nuclear magnetic resonance (NMR) spectroscopy using the 29Si isotope provide limited structural information, while scattering an microscopy techniques are complex and unsuitable for routine or industrial use. This thesis addresses this gap by developing a fluorescence-based nanometrology platform that combines advanced spectroscopy and microscopy with computational modelling, offering a scalable framework for particle sizing and mechanistic insight. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations were used to investigate the interactions of Rhodamine 6G (R6G) with silica nanoparticles (SNPs). Adsorption strength was found to depend on nanoparticle curvature, crystallinity, and pH, with larger SNPs and hydroxyl-rich surfaces favouring stable binding. Crucially, adsorption occurred even at the isoelectric point, highlighting the role of van der Waals forces beyond electrostatics. Simulations also showed R6G dimerisation, which quenches fluorescence, occurs primarily in solution rather than on the silica surface due to structural constraints, providing a molecular-level explanation for how adsorption and aggregation influence fluorescence. Experimental validation used time-resolved fluorescence anisotropy and fluorescence recovery after photobleaching (FRAP). Anisotropy-based methods yielded reliable hydrodynamic radii for sodium silicate systems, agreeing with small-angle X-ray scattering (SAXS), and demonstrated the influence of dye flexibility on size determination. FRAP proved particularly powerful, resolving distinct particle populations in complex colloids and detecting changes in viscosity, dye concentration, and aggregation. Larger SNPs consistently exhibited stronger dye binding and more stable fluorescence, confirming computational predictions. This work unites modelling and experiment to create a multiscale fluorescence-based nanometrology approach. Compared with dynamic light scattering (DLS), transmission electron microscopy (TEM), or SAXS, the platform offers rapid, non-invasive, and sample-efficient characterisation. Its ability to probe both average and spatially resolved particle sizes provides new insights into colloidal stability and structural evolution. Beyond advancing fluorescence imaging as a nanometrology tool, the results highlight broader opportunities for integrating simulation and spectroscopy in the study of soft matter and industrially relevant materials.
Advisor / supervisor
  • Chen, Yu
  • Kubiak-Ossowska, Karina
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