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TY - THES AU - Fokina, Vladislava TI - Control of nanoparticle self-assembly PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2024-05179 SP - 1 Online-Ressource : Illustrationen PY - 2024 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, RWTH Aachen University, 2024 AB - 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. LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2024-05179 UR - https://publications.rwth-aachen.de/record/986347 ER -