Author

Yao WuFollow

Degree

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Document Type

Dissertation

Abstract

The ability to explore and predict metastable structures of hybrid self-assemblies is of central importance for the next generation of advanced materials with novel properties. As compared to their thermodynamically stable forms, the kinetically stabilized materials show improved functionality potentially over their stable counterparts. The self-assembly processes usually originate from weak intermolecular interactions, involving a dynamic competition between attractive and repulsive interactions. These weak forces, including van der Waals (vdW), electrostatic interaction and the hydrogen bonding (H-bonding), can be tuned by external stimuli, e.g., confinement, temperature and ionization, and consequently driving hybrid materials into different configurations. It is challenging to determine the mechanisms and design rules for guiding a system into particular metastable states. Therefore, as a starting point, the focus of this dissertation is to understand how these interactions vary as a function of external parameters to determine why a particular equilibrium structure emerges. This information can not only be used to understand the mechanisms responsible for a system choosing a particular configuration, but also as a reference for future studies of metastable configurations with the long-term goal of developing rules for experimentalists to use in synthesizing hybrid materials into metastable states. In this dissertation, we studied the assembly processes of both ionic and non-ionic amphiphiles with silica that exhibit all three molecular interactions. By judiciously choosing three particular systems, the complex coupled nature of these interactions can be separated, allowing for each interaction to be isolated and systematically studied. For globular/silica hybrid system, the orientation of adsorbed protein depends on electrostatic interactions that can be tuned via ionization of silica; the morphologies of silica-adsorbed fatty acids are related to the competition between electrostatic and vdW interaction as a function of fatty acids’ ionized degree; the phase behavior of ethoxylated surfactants in silica pores can be programmed by tuning the H-bonding as a function of temperature and confinement. For the first time, the atomic interactions at the amphiphile/silica interfaces are studied systematically to set up a basis for choosing the appropriate assembly environments to modulate the structures of a wide range of amphiphiles for wet bench research.

Committee Chair

Shelton, William A

Available for download on Saturday, December 18, 2021

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