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Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2014 (English)In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 8, 1443-1450 p.Article in journal (Refereed) Published
Abstract [en]

The growth modes of self-assembled mesocrystals and ordered arrays from dispersions of iron oxide nanocubes with a mean edge length of 9.6 nm during controlled solvent removal have been investigated with a combination of visible light video microscopy, atomic force microscopy and scanning electron microscopy. Mesocrystals with translational and orientational order of sizes up to 10 mu m are formed spontaneously during the final, diffusion-controlled, drop-casting stage when the liquid film is very thin and the particle concentration is high. Convection-driven deposition of ordered nanocube arrays at the edge of the drying droplet is a manifestation of the so called coffee-ring effect. Dendritic growth or fingering of rapidly growing arrays of ordered nanocubes could also be observed in a transition regime as the growth front moves from the initial three-phase contact line towards the centre of the original droplet.

Place, publisher, year, edition, pages
2014. Vol. 16, no 8, 1443-1450 p.
National Category
Chemical Sciences
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-101752DOI: 10.1039/c3ce41871eISI: 000330781000006OAI: oai:DiVA.org:su-101752DiVA: diva2:705864
Funder
Swedish Research Council
Note

AuthorCount:5;

Available from: 2014-03-18 Created: 2014-03-14 Last updated: 2017-12-05Bibliographically approved
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.
Keyword
Self-assembly, iron oxide nanocubes, mesocrystal, small angle X-ray scattering, video microscopy, QCM-D
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-132582 (URN)978-91-7649-402-8 (ISBN)
Public defence
2016-10-06, Magnéli Hall, Arrhenius Laboratory, Universitetsvägen 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Note

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: 2017-03-03Bibliographically approved

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Agthe, MichaelWetterskog, ErikSalazar-Alvarez, GermanBergström, Lennart
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