Dokument: Structural and Optical Properties of Plasmonic Core-Shell Microgels and their 2D Assemblies
| Titel: | Structural and Optical Properties of Plasmonic Core-Shell Microgels and their 2D Assemblies | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=70392 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20250731-130313-4 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Feller, Déborah [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Karg, Matthias [Gutachter] Prof. Dr. Crassous, Jérôme [Gutachter] | |||||||
| Stichwörter: | core-shell microgels, plasmonic nanoparticles, in situ extinction spectroscopy, small-angle neutron scattering, monolayers, 2D non-close-packed Bravais lattices | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | Hybrid microgels with a rigid, inorganic core and a soft, polymeric shell are highly interesting for fundamental and applied science due to their - often synergistic - properties originating from both the core and the shell. A prominent example is gold nanoparticle core-poly(N-isopropylacrylamide) (PNIPAM) shell microgels. These microgels exhibit an optical response which arises from two primary contributions: the localized surface plasmon resonance (LSPR) of the gold nanoparticle and the strong scattering from the PNIPAM shell. To enhance the plasmonic properties, the gold cores are overgrown in situ within the shell, increasing their size and absorbance. This results in a stronger plasmonic signal that can outweigh the scattering contribution of the shell. At the same time, the crosslinked PNIPAM shell renders such colloids with thermoresponsive properties due to the lower critical solution temperature behavior of PNIPAM in water. The polymeric shell further enables adsorption of the microgels at fluid interfaces and promotes their self-assembly into hexagonally ordered arrangements with interparticle distances in the range of the wavelength of visible light. Here, the shell acts as stabilizer and spacer for the gold cores. These arrangements can be transferred onto substrates to form periodic coatings that feature pronounced plasmonic properties. Even though they find application in the field of, e.g., sensing, only little is known about the interplay of the structural properties and the interface-assisted assembly behavior of such microgels.
This thesis investigates the structural and optical properties of plasmonic core-shell microgels and their suitability as colloidal building blocks for the preparation of plasmonic monolayers through interface-assisted assembly. One objective is to investigate the microgels before and after the overgrowth of the core in situ within the shell. Small-angle scattering techniques are used to follow the core growth, but more importantly to investigate the resulting change in the local morphology of the microgel shells – a change that has not been addressed so far. Crucial for the clarification of the structural changes are the pronounced differences in contrast of the cores and the shells for neutrons and X-rays. While the cores primarily contribute to the scattering signal in X-ray scattering experiments, the polymeric shells provide excellent contrast in neutron scattering. Prior to core overgrowth, the scattering profiles of the microgels are described by an exponential shell form factor model, whereas the scattering profiles of the microgels after the core overgrowth significantly deviate from the common form factor models. Consequently, reverse Monte-Carlo simulations are employed to reveal structural changes within the polymer shell induced by the overgrowth of the core. While the overall dimensions of the microgels do not significantly change, as revealed by, e.g., dynamic light scattering, analysis by transmission electron microscopy and reverse Monte Carlo simulations point to a densification of the polymer shell in the close vicinity of the gold nanoparticle cores upon in situ overgrowth of those. The thesis further explores the fabrication of non-hexagonal, plasmonic monolayers using fluid interface-assisted assembly. Typically, the microgels assemble at fluid interfaces and are then transferred to a substrate resulting in a hexagonally ordered monolayer. By adjusting parameters such as transfer direction, speed and substrate contact angle, 2D non-close-packed Bravais lattices of gold nanoparticles are obtained. All five lattices exhibit pronounced LSPR peaks as shown by extinction spectroscopy and supported by finite difference time domain simulations. The lattices show surface lattice resonance, if the RI environment around the gold nanoparticle cores is adjusted to enable plasmonic-diffractive coupling. Further it is proven that the transfer process is applied to microgels with different dimensions resulting in the same lattices with other periodicities. A novel aspect of this research is the in situ measurements of monolayers of plasmonic core-shell microgels at the air/water interface. This is achieved by using a Langmuir trough combined with an optical fiber-based extinction spectrometer. In situ spectroscopy is performed on plasmonic monolayers with interparticle distances in the range of the wavelength of visible light. At the interface, resonance coupling with in-plane diffractive modes is enabled. This is followed in dependence of interparticle distance, controlled through uniaxial compression of the monolayer. A shift of the resonance peak is observed during the reduction of the total interfacial area. These findings are validated by COMSOL simulations which support that at large interparticle distances plasmonic-diffractive coupling is enabled providing a sharp narrow surface lattice resonance peak. This study provides a deeper understanding of not only the plasmonic response, but also of the interfacial behavior of assembled microgels in dependence of their packing fraction. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie » Physikalische Chemie und Elektrochemie | |||||||
| Dokument erstellt am: | 31.07.2025 | |||||||
| Dateien geändert am: | 31.07.2025 | |||||||
| Promotionsantrag am: | 23.04.2025 | |||||||
| Datum der Promotion: | 17.07.2025 |
