Synthesis and characterization of highly stable functional silica nanoparticles for LbL assembly
Barak, Melike (2018) Synthesis and characterization of highly stable functional silica nanoparticles for LbL assembly. [Thesis]
Layer by Layer (LbL) assembly is a superior method to create thin films with aqueous based dispersions which include polyelectrolytes and nanoparticles. LbL presents exceptional advantages like conformal coatings with controlled structure and composition by using electrostatic interactions of oppositely charged materials. Nevertheless, these interactions may cause weaker mechanical properties on the thin films. In order to eliminate the drawback, the covalent bond between oppositely charged materials can establish by crosslinking of functional groups. Silica nanoparticles are mostly used in the LbL process due to enhance adhesion of films by creating roughness on the surface. They are also suitable for surface modification which provides surface charge manipulation, stable dispersibility and good mechanical property. Silane alkoxy groups are one of the best choices for functionalization process. These coupling agents promote mechanical robustness of the surface via the formation of physically and chemically stable covalent bonds. In this study, silica nanoparticle was synthesized by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in surfactant/cyclohexane/ammonia media by microemulsion method. Monodisperse and having around 50 nm diameter silica nanoparticles were achieved to use in further steps. Amino and poly (ethylene glycol)-terminated alkoxy silanes were performed to ensure positive and negative surface charges on the silica nanoparticles surface by crosslinking. The functionalized silica nanoparticles were utilized in LbL process, right after poly allylamine hydrochloride (PAH) and poly (sodium 4-styrenesulfonate) (SPS) were applied in desired number of layers on the silicon wafer substrates. Dynamic light scattering (DLS) is employed to analyze size and surface charge distribution of bare and functionalized silica nanoparticles. The presence of functional groups was examined by Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The thickness, surface topography and roughness of thin films are measured by ellipsometry and atomic force microscopy (AFM). Scanning electron microscopy (SEM) was performed to analyze nanostructural morphology of silica nanoparticle and thin films. The obtained results indicated that chemically crosslinked silica nanoparticle containing thin films exhibit better mechanical properties that make them useful for desired applications.
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