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Crystallization on ...
Crystallization on the Mesoscale : Self-Assembly of Iron Oxide Nanocubes into Mesocrystals
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- Agthe, Michael, 1983- (author)
- Stockholms universitet,Institutionen för material- och miljökemi (MMK)
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- Bergström, Lennart, Professor (thesis advisor)
- Stockholms universitet,Institutionen för material- och miljökemi (MMK)
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- Salazar-Alvarez, German, Assoc. Professor (thesis advisor)
- Stockholms universitet,Institutionen för material- och miljökemi (MMK)
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- Nylander, Tommy, Professor (opponent)
- Lund Unviersity, Lund, Sweden
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(creator_code:org_t)
- ISBN 9789176494028
- Stockholm : Department of Materials and Environmental Chemistry, Stockholm University, 2016
- English 64 s.
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Abstract
Subject headings
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- Self-assembly of nanoparticles is a promising route to form complex, nanostructured materials with functional properties. Nanoparticle assemblies characterized by a crystallographic alignment of the nanoparticles on the atomic scale, i.e. mesocrystals, are commonly found in nature with outstanding functional and mechanical properties. This thesis aims to investigate and understand the formation mechanisms of mesocrystals formed by self-assembling iron oxide nanocubes.We have used the thermal decomposition method to synthesize monodisperse, oleate-capped iron oxide nanocubes with average edge lengths between 7 nm and 12 nm and studied the evaporation-induced self-assembly in dilute toluene-based nanocube dispersions. The influence of packing constraints on the alignment of the nanocubes in nanofluidic containers has been investigated with small and wide angle X-ray scattering (SAXS and WAXS, respectively). We found that the nanocubes preferentially orient one of their {100} faces with the confining channel wall and display mesocrystalline alignment irrespective of the channel widths. We manipulated the solvent evaporation rate of drop-cast dispersions on fluorosilane-functionalized silica substrates in a custom-designed cell. The growth stages of the assembly process were investigated using light microscopy and quartz crystal microbalance with dissipation monitoring (QCM-D). We found that particle transport phenomena, e.g. the coffee ring effect and Marangoni flow, result in complex-shaped arrays near the three-phase contact line of a drying colloidal drop when the nitrogen flow rate is high. Diffusion-driven nanoparticle assembly into large mesocrystals with a well-defined morphology dominates at much lower nitrogen flow rates. Analysis of the time-resolved video microscopy data was used to quantify the mesocrystal growth and establish a particle diffusion-based, three-dimensional growth model. The dissipation obtained from the QCM-D signal reached its maximum value when the microscopy-observed lateral growth of the mesocrystals ceased, which we address to the fluid-like behavior of the mesocrystals and their weak binding to the substrate. Analysis of electron microscopy images and diffraction patterns showed that the formed arrays display significant nanoparticle ordering, regardless of the distinctive formation process. We followed the two-stage formation mechanism of mesocrystals in levitating colloidal drops with real-time SAXS. Modelling of the SAXS data with the square-well potential together with calculations of van der Waals interactions suggests that the nanocubes initially form disordered clusters, which quickly transform into an ordered phase.
Subject headings
- NATURVETENSKAP -- Kemi -- Materialkemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences -- Materials Chemistry (hsv//eng)
Keyword
- Self-assembly
- iron oxide nanocubes
- mesocrystal
- small angle X-ray scattering
- video microscopy
- QCM-D
- Materials Chemistry
- materialkemi
Publication and Content Type
- vet (subject category)
- dok (subject category)
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