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Precise control over shape and size of iron oxide nanocrystals suitable for assembly into ordered particle arrays
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2014 (English)In: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514Article in journal (Refereed) Published
Abstract [en]

Here we demonstrate how monodisperse iron oxide nanocubes and nanospheres with average sizes between 5 and 27 nm can be synthesized by thermal decomposition. The relative importance of the purity of the reactants, the ratio of oleic acid and sodium oleate, the maximum temperature, and the rate of temperature increase, on robust and reproducible size and shape-selective iron oxide nanoparticle synthesis are identified and discussed. The synthesis conditions that generate highly monodisperse iron oxide nanocubes suitable for producing large ordered arrays, or mesocrystals are described in detail.

Place, publisher, year, edition, pages
National Category
Materials Chemistry
URN: urn:nbn:se:su:diva-129566DOI: 10.1088/1468-6996/15/5/055010OAI: diva2:923222
Available from: 2016-04-25 Created: 2016-04-25 Last updated: 2016-08-16
In thesis
1. Crystallization on the Mesoscale: Self-Assembly of Iron Oxide Nanocubes into Mesocrystals
Open this publication in new window or tab >>Crystallization on the Mesoscale: Self-Assembly of Iron Oxide Nanocubes into Mesocrystals
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2016. 64 p.
Self-assembly, iron oxide nanocubes, mesocrystal, small angle X-ray scattering, video microscopy, QCM-D
National Category
Materials Chemistry
Research subject
Materials Chemistry
urn:nbn:se:su:diva-132582 (URN)978-91-7649-402-8 (ISBN)
External cooperation:
Public defence
2016-10-06, Magnéli Hall, Arrhenius Laboratory, Universitetsvägen 16 B, Stockholm, 13:00 (English)
Swedish Research Council

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2016-09-13 Created: 2016-08-15 Last updated: 2016-09-02Bibliographically approved

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