Controlled synthesis of organic-inorganic composite particles

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2022-8-26

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Erçelik, Elif

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Liquid crystal (LC) is a state of matter having long-range orientational order between crystalline solid and isotropic liquid, and its molecular orientation can be altered with external stimuli. The polymerization of liquid crystal droplets has been widely used for the synthesis of LC-templated functional materials due to its ordering property and fluidic behavior. In this study, we investigated the synthesis of composite particles with controlled internal and interfacial structure using surface-modified nanoparticles-adsorbed LC droplets as templates. In the first part of this study, we synthesized silica nanoparticles, silver nanoparticles, and iron oxide nanoparticles and modified their surfaces by using thiol or silane groups to procure either planar, tilted, or homeotropic anchoring to LC droplets and pH-dependent surface charge, hydrophobicity, and hydrophilicity. Secondly, we adsorbed nanoparticles to the LC-aqueous interface and characterized the configurations (internal structuring) of LC droplets. We showed that surface chemistry, concentration, and surface charging of nanoparticles affect the change in configuration of LC droplets and form heterogeneity on the surface. According to our results, adsorption of silver and iron oxide nanoparticles modified with 1-decanethiol and 1-hexadecanethiol (-C10/C16 mixed monolayers of thiols) showed a transition from bipolar to radial, whereas -COOH/C16 mixed monolayers of thiol terminated nanoparticles (tilted) changed the configuration to preradial. Adsorption of silica nanoparticles modified with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP, homeotropic) and -COOH/DMOAP terminated counterparts exhibited a configuration change from bipolar to radial and preradial, respectively. -NH2 and -COOH terminated counterparts (planar) did not change the configuration. Thirdly, we used -NH2 and -COOH terminated silica nanoparticles with different sizes (51.2 nm ± 9.0 nm to 417.1 nm ± 22.1 nm), tuned their surface charges by changing pH, and finally polymerized the LC droplets after adsorption. Charging property of -NH2 and -COOH terminated silica nanoparticles provided adsorption control. We showed partial coverage of charged, surface-modified silica nanoparticles to enable their preferential positioning, which offered control over the interfacial structure for composite particles. These results in this study provide a basis for synthesizing anisotropic, polymeric composite particles with complex structures for technological products, biomedical or sensing applications.

Subject Keywords

Liquid crystal emulsions, Nanoparticles, Internal structuring, Surface charge, Polymerization

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https://hdl.handle.net/11511/98692

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

E. Erçelik, “Controlled synthesis of organic-inorganic composite particles,” M.S. - Master of Science, Middle East Technical University, 2022.