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Crystallization on the Mesoscale: Self-Assembly of Iron Oxide Nanocubes into Mesocrystals
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0002-2068-6201
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. , p. 64
Keywords [en]
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: urn:nbn:se:su:diva-132582ISBN: 978-91-7649-402-8 (print)OAI: oai:DiVA.org:su-132582DiVA, id: diva2:952962
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: 2022-02-23Bibliographically approved
List of papers
1. Precise control over shape and size of iron oxide nanocrystals suitable for assembly into ordered particle arrays
Open this publication in new window or tab >>Precise control over shape and size of iron oxide nanocrystals suitable for assembly into ordered particle arrays
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2014 (English)In: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 15, no 5, article id 055010Article 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.

Keywords
iron oxide, nanoparticles, synthesis, assembly, superlattice, mesocrystal
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-129566 (URN)10.1088/1468-6996/15/5/055010 (DOI)000345025600014 ()
Available from: 2016-04-25 Created: 2016-04-25 Last updated: 2022-03-23Bibliographically approved
2. Controlling Orientational and Translational Order of Iron Oxide Nanocubes by Assembly in Nanofluidic Containers
Open this publication in new window or tab >>Controlling Orientational and Translational Order of Iron Oxide Nanocubes by Assembly in Nanofluidic Containers
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2015 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 45, p. 12537-12543Article in journal (Refereed) Published
Abstract [en]

We demonstrate that spatial confinement can be used to control the orientational and translational order of cubic nanoparticles. For this purpose we have combined X-ray scattering and scanning electron microscopy to study the ordering of iron oxide nanocubes that have self-assembled from toluene-based dispersions in nanofluidic channels. An analysis of scattering vector components with directions parallel and perpendicular to the slit walls shows that the confining walls induce a preferential parallel alignment of the nanocube (100) faces. Moreover, slit wall separations that are commensurate with an integer multiple of the edge length of the oleic acid-capped nanocubes result in a more pronounced translational order of the self-assembled arrays compared to incommensurate confinement. These results show that the confined assembly of anisotropic nanocrystals is a promising route to nanoscale devices with tunable anisotropic properties.

National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-124758 (URN)10.1021/acs.langmuir.5b03678 (DOI)000365150700026 ()26509355 (PubMedID)
Available from: 2016-01-08 Created: 2016-01-04 Last updated: 2022-02-23Bibliographically approved
3. Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes
Open this publication in new window or tab >>Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes
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2014 (English)In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 8, p. 1443-1450Article 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.

National Category
Chemical Sciences
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-101752 (URN)10.1039/c3ce41871e (DOI)000330781000006 ()
Funder
Swedish Research Council
Note

AuthorCount:5;

Available from: 2014-03-18 Created: 2014-03-14 Last updated: 2022-03-23Bibliographically approved
4. Following the mesocrystal growth of self-assembling iron oxide nanocubes by video microscopy and quartz crystal microbalance with dissipation monitoring
Open this publication in new window or tab >>Following the mesocrystal growth of self-assembling iron oxide nanocubes by video microscopy and quartz crystal microbalance with dissipation monitoring
(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-132590 (URN)
Available from: 2016-08-16 Created: 2016-08-16 Last updated: 2022-02-23Bibliographically approved
5. Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops
Open this publication in new window or tab >>Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops
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2016 (English)In: Nano Letters, ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 11, p. 6838-6843Article in journal (Refereed) Published
Abstract [en]

Mesocrystals composed of crystallographically aligned nanocrystals are present in biominerals and assembled materials which show strongly directional properties of importance for mechanical protection and functional devices. Mesocrystals are commonly formed by complex biomineralization processes and can also be generated by assembly of anisotropic nanocrystals. Here, we follow the evaporation-induced assembly of maghemite nanocubes into mesocrystals in real time in levitating drops. Analysis of time-resolved small-angle X-ray scattering data and ex situ scanning electron microscopy together with interparticle potential calculations show that the substrate-free, particle-mediated crystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals. Controlling and tailoring the particle-mediated formation of mesocrystals could be utilized to assemble designed nanoparticles into new materials with unique functions.

Keywords
Mesocrystal, anisotropic nanoparticles, SAXS, two-step crystallization, acoustic levitation
National Category
Chemical Sciences
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-136757 (URN)10.1021/acs.nanolett.6b02586 (DOI)000387625000019 ()
Available from: 2016-12-14 Created: 2016-12-14 Last updated: 2022-02-28Bibliographically approved

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