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Authors: Kang, Eunsoo
Title: Controlling Hypersonic Particle Resonances through Tailored Colloidal Synthesis
Online publication date: 3-Jun-2020
Language: english
Abstract: For decades, the application spectrum of nano-scaled materials has been widened. But, there is still a demand to exploit new physical behavior of those materials. Nano-scaled materials usually show distinctive properties compared to the bulk state, which is in particular the case for mechanical, thermal and phononic properties, as demonstrated in this work for different types of nano-scaled colloidal structures. In this thesis, the synthesis, the self-assembly of colloids, the characterization, and the particle vibration spectroscopy utilizing Brillouin light scattering (BLS) spectroscopy are described. Control over the hypersonic resonance of polymer colloids requires tailored colloidal synthesis. Various types of particles with narrow size distribution were synthesized and colloidal structures (i.e., face-centered cubic) on solid substrates (glass or silicon wafer) were prepared by drop-evaporation method or vertical lift deposition. The samples were investigated by BLS spectroscopy to study the colloid mechanical resonances and interparticle interactions. BLS is a high-resolution spectroscopic method that can sensitively detect particle vibrations in the GHz regime through inelastic light scattering in analogy to THz Raman molecular vibration spectroscopy. Access to particle vibrations and interactions allow estimation of colloid elastic moduli, glass transition, and direct observation of the surface mobility, respectively. The experimental results yielded the following information: First, polystyrene (PS) nanoparticles (NPs) with different chemical compositions (different comonomers) have distinct particle interactions, elastic modulus, and surface softening temperature (Ts). Second, surface tuning of PS NPs were achieved by chemical and physical methods; (i) chemically bonded groups (by two-step surfactant-free polymerization), (ii) physically adsorbed groups (by layer-by-layer adsorption method) led to PS NP systems with thin (8 ~ 18 nm for chemically bonded groups, 1 ~ 2 nm for physically adsorbed groups) shells atop the PS core. The presence of the thin shell modified particle interactions, elastic modulus, Ts, and glass transition temperature (Tg > Ts). Third, poly (butyl methacrylate) (PBMA), a low Tg (~ 290 K) polymer compared to the PS core, was introduced on top of the PS core with different PBMA thicknesses. For this core-shell NP structure, the shear modulus decreased with increasing PBMA shell thickness. Interestingly, while the Tg of the PS core was virtually constant, an elevation of the Tg of PBMA shell was found with decreasing PBMA thickness. Overall the results in this dissertation suggest that nanoparticle modulus and thermomechanical behavior can be tuned independently through tailored particle architectures and compositions. In addition, it is shown that BLS is a non-contact and no destructive sensitive spectroscopy method that can provide elastic modulus and thermal properties of nanoparticles. The results from BLS were complemented with the finite element method (FEM), and modulated differential scanning calorimetry (MDSC).
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Externe Einrichtungen
Place: Mainz
Version: Original work
Publication type: Dissertation
License: in Copyright
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Extent: IX, 128 Seiten
Appears in collections:JGU-Publikationen

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