UC Irvine

The interface between two phases of matter is an interaction polestar, a chemically rich intermolecular hub often fraught with science unexplored. May it be the liquid/vapor interfaces of our oceans, rivers and aqueous cloud-based droplets suspended in the atmosphere, or the hydrated solid/liquid interfaces of industrial catalysts and electrodes found in batteries, fuel cells or groundwater remediation plants. No matter the choice, we are regularly exposed to interfaces and staunchly rely on an evolving knowledge-base of such systems to enhance the quality of life.

The work to be presented in the following thesis will include the studies of both liquid/vapor and solid/liquid interfaces using experimental and computational techniques. In Chapter 1 is an experimental background highlighting the development of X-ray Photoelectron Spectroscopy toward its use of probing the liquid/vapor interface of liquid micro-jets and the adaptation of this technique to permit near ambient pressures in the sample analysis chamber. The experimental system utilized for the studies herein may be found in Appendix A.

Also included in Chapter 1 is a general background on the computational methods required for simulating molecular trajectories of the systems in question. To follow, in Chapter 2, is a description of the program that I have written that evaluates the instantaneous interface of a liquid solution. Input and output les are considered for proper use of the program, and the source is provided in Appendix B.

Chapter 3 is a highly comprehensive evaluation of the solvation of 1- and 2-propanol at the surface of aqueous solutions. Results presented are of liquid-jet ambient pressure X-ray Photoelectron Spectroscopy and classical Molecular Dynamics simulations. The direction of these studies were toward elucidating surface concentration, density and orientation effects upon changing the bulk alcohol concentration. The two systems were compared to learn of differences due to elementally identical, but geometrically dissimilar molecules. Discussed is the observation of surface concentration enhancements, orientational ordering and trends of the surface atom populations over varying bulk concentration.

Chapter 4 is of the investigation of the solid/liquid interface of suspended titanium dioxide nanoparticles in a high ionic strength, aqueous, nitric acid electrolyte. The goal here was to investigate the affect that the surrounding ions have on the nanoparticle surface. It was the first study to successfully observe band bending at the solid/liquid interface of a colloidal TiO2 nanoparticle in bulk electrolyte solution.