Doctor of Philosophy (PhD)
Cain department of chemical engineering
Molecular and nanoscale colloids such as surfactant, fatty acid and metallic nanoparticles are widely used in numerous applications such as detergents, biomedicine, and catalyst. The assemblies of these colloids show different morphological behavior in aqueous solution due to the wide range of intermolecular interactions such as hydrogen bonding, van der Waals, and electrostatics. The morphology of these assemblies can be changed by environmental factors including temperature, ionic strength, and salinity. However, the guidance to direct assembled state of colloidal assemblies at heterogenous interfaces under various external stimuli remains poorly understand. In this Ph.D. dissertation, we show the adsorption and reconfiguration of nanostructures on liquid-solid and liquid-vapor interfaces using adsorption isotherms, spectrophotometry, and small angle neutron scattering techniques.
The adsorption and self-assembly at solid-liquid interface are investigated using nonionic, ionic amphiphiles, and metallic nanoparticles as model materials. We show that the binding and reorganization of these assemblies on silica-based adsorbents are impacted by temperature, presence of counterions, and dispersion salinity. The effect of temperature on morphological change of nonionic surfactant (“soft matter”) in silica pore is first studied, and this change is attributed to the change in hydration state of the headgroups of the surfactant. We further investigate the assembled state of “hard matter” i.e. gold nanoparticle in propylamine modified silica porous materials, and we demonstrate the spatial distribution and catalysis activity of gold nanoparticles in different pore size silica porous materials in dispersion of increasing salinity. Moreover, the effect of counterion on the surface organization of fatty acid adsorbed on silica nanoparticle is uncovered. We find that the phase behavior of fatty acid on silica surface is governed by their ionization state, and we report that the interfacial activities of fatty acid-based materials regulate the stability of liquid-vapor interface i.e. foam in aqueous solution. We extend this concept to a long-term thermostimulable foam in high alcohol solvents (> 75 vol%) formed by the natural fatty acid crystals. My Ph.D. works provide fundamental science to surface chemistry of molecular and nanoscale colloids, which is crucial in the development of new multiresponsive materials, personal care products, cosmetics and sensors.
Ma, Yingzhen, "Assembly of Nanostructures at Solid-Liquid and Liquid-Air Interfaces" (2022). LSU Doctoral Dissertations. 5839.
Available for download on Saturday, April 08, 2023