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Tunable self assembly of crystals and branching chain networks
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
University of Basel.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.ORCID iD: 0000-0002-7517-8204
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-365206OAI: oai:DiVA.org:uu-365206DiVA, id: diva2:1262347
Available from: 2018-11-11 Created: 2018-11-11 Last updated: 2018-11-12
In thesis
1. Self-assembly of magnetic particles
Open this publication in new window or tab >>Self-assembly of magnetic particles
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Self-assembly is the spontaneous formation of larger structures from small building blocks. This process is driven and determined by the interactions between the constituents. Examples of self assembly are found almost everywhere and, in particular, biological systems in general rely on a hierarchical formation of structures over a range of length scales. Technologically, self-assembly can be used to form mesoscopic structures and artificial crystals. In the case of particles with micrometer size suspended in a liquid phase, it is possible to use optical microscopy for the the investigation of self-assembly.

In this thesis, the self-assembly of microbeads with tunable magnetic interactions is studied, based on the statistic analysis of microscope images and computer simulations. Magnetic and non-magnetic microbeads are suspended in a ferrofluid, which is a dispersion of magnetic nanoparticles in water. As a result, the magnetic properties of the microbeads in the ferrofluid are altered and can be described by effective magnetic susceptibilities and magnetic dipole moments, which can be tuned continuously. The liquid is confined between glass slides and effectively the microbeads are studied in a 2D geometry under a magnetic field, applied either in- or out-of-plane. The resulting structures are detected by image analysis algorithms, analyzed and correlated to the dipolar interaction between the beads, as well as to macroscopic quantities, like the particle density and ratio. For the in-plane field a phase transition from square to hexagonal lattice is observed. This phase transition is explained by the change in dipole interaction between the microbeads as the moments change from anti-parallel to parallel alignment.  For the out-of-plane field the situation becomes diverse and more phases appear. It turns out that the phase formation in this case is strongly dependent on the bead ratio, density and interactions.

We identify regions in the phase diagram, where isolated beads, percolated structures, and crystals dominate. To cover a wide parameter range the experiments are complemented by computer simulations. The tools developed in this thesis enable us to construct phase diagrams extracted from direct imaging and dependence on the extracted relevant parameters.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 47
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1742
Keywords
self-assembly, tunable interactions, phase transition, ferrofluid
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-364557 (URN)978-91-513-0500-4 (ISBN)
Public defence
2018-12-19, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Carl Tryggers foundation
Available from: 2018-11-28 Created: 2018-10-30 Last updated: 2018-12-27

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Carstensen, HaukeKapaklis, VassiliosWolff, Max

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