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@PHDTHESIS{Fokina:986347,
author = {Fokina, Vladislava},
othercontributors = {Förster, Stephan Friedrich and Richtering, Walter},
title = {{C}ontrol of nanoparticle self-assembly},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-05179},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2024},
abstract = {Core-shell nanoparticles are hybrid systems that
self-assemble into complex structures with exceptional
characteristics. Inorganic and polymeric core-shell
nanoparticles are widely used for biomedical and industrial
applications. The precise control of the nanoparticle
assembly process is crucial for obtaining well-defined
structures with desired properties and functions. For that,
internal parameters of a system must be tuned, such as the
core-shell ratio, the constituting materials, and the
solvent type. Additionally, nanoparticle assembly can be
impacted by external conditions, e.g. by shearing, magnetic
fields, and temperature, which potentially leads to the
formation of highly ordered structures. The structural
variability of core/shell particles allows to obtain a
diversity of materials with specific structures. The
challenge is to develop a fundamental understanding of the
relation between the core/shell structure and the
hierarchical structure of the obtained material. The general
tendency of core-shell nanoparticle to assemble into
specific structures can be described using phase diagrams.
Depending on such parameters of spherical particles like
core volume fraction and core-to-shell ratio, resultant
self-assembly structures can thus be classified into a range
of phases from the highly-symmetric face-centered cubic
phase to low-symmetry quasicrystals. In the current work,
the solution self-assembly of hard- and soft-core core/shell
nanoparticles are systematically investigated using
small-angle X-ray scattering under shear, and transmission
electron microscopy. The lyotropic liquid crystals and their
lattices formed by self-assembly of the core/shell
nanoparticles are then compared to predicted structures from
molecular dynamic simulations and integrated into phase
diagrams. In the first part of the thesis, defined system
parameters and external conditions for the formation and
orientation of the A15 Frank-Kasper phase formed by micellar
structures in water are presented. The role of polymer
concentration and the size distribution of its hydrophobic
part is highlighted. In the second part, another type of
soft-core nanoparticle, polyisoprene-polystyrene micelles in
organic solvents, are investigated with respect to the
formation of quasicrystal phases. Previous knowledge about
the rheological behavior of the polymer system provided a
starting point for a new cuvette-type rheo-SAXS shearing
device, which expanded the technical possibilities of
shearing experiments and the studied materials. Besides,
measurements of PI-PS solutions revealed specific insights
in FCC-BCC phase coexistence during temperature changes and
at applied high strains. In the third part of the thesis,
hard-core nanoparticles are investigated. For hard core
core/shell nanoparticles, core deformation during shearing
as happens to soft matter systems is prevented. Synthesis
conditions to control the core size of superparamagnetic
magnetite nanoparticles (SPIONS) over a wide range are
explored. SPIONs are synthesized using the thermal
decomposition method that delivers spherical, uniform,
monodisperse, and monocrystalline particles up to 24 nm
diameter. Various paths of synthesis demonstrate the
influence of the solvent type and the thermal pretreatment
of precursor on resultant particles. Especially, their size,
shape, and quality are essential for assembly in magnetic
fields. Shearing and magnetic external fields are powerful
instruments for structure ordering and orientation, which
enable phase transitions and the adjustment of lattice
parameters. Polymer-grafted SPIONs are investigated as
hard-core core/shell nanoparticles with respect to the
formation of ordered FCC phases. It is found that shearing
in combination with a permanent magnetic field leads to
complex structural reorientation processes. For particular
core-shell nanoparticles of 14 and 24 nm diameter, the
influence of a permanent magnetic field during a long-time
exposure causes well-defined disorder-BCC-FCC phase
transitions. These studies conclude the investigations on
the influence of core/shell-structure and external shear and
magnetic fields on the self-assembly hard and soft core
core/shell nanoparticles.},
cin = {155710 / 150000},
ddc = {540},
cid = {$I:(DE-82)155710_20190327$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-05179},
url = {https://publications.rwth-aachen.de/record/986347},
}
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