Water is the most precious substance on our planet. Environmental concerns about adequate clean water resources have increasingly become more global with the recognition that unwanted chemicals in the atmosphere, in our soils and in our surface waters often transport well beyond the national boundaries of origin. As a result, there is a growing international urgency to understand environmental issues that can cross boundaries with climate change, healthy air quality and clean water resources being the most obvious. The focus of the studies in the Richmond Laboratory is to provide fundamental insights into molecular processes that underlie some of the aforementioned global concerns, with a particular focus on understanding environmentally important processes that occur at water surfaces and aqueous-oil boundary layers.
Ongoing Research Projects: The current studies fall into two interrelated areas. The first studies examine environmentally important chemistry that occurs on atmospheric aerosols, and marine and fresh water surfaces. on the nature of adsorption, solvation and reactivity of gases and small organic molecules on the surface of aqueous solutions. How these processes depend on temperature, solution composition and surface energetics is being examined. The systems selected for study are ones that play a central role in the environmentally important chemistry that occurs on atmospheric aerosols, and marine and fresh water surfaces.
The second area of study focuses on understanding what happens to the molecular behavior of the surface of water when covered with oil and how surfactants, dispersants and polymers assemble and organize at that fluid junction. Knowledge gained from these studies have direct relevance to understanding important issues including the interaction of water with soils, metal ion transport across membranes, toxic metal complexation and oil spill remediation. These studies are conducted both on planar oil/water interfaces as well as on the surface of nanoemulsions, small droplets of oil suspended in water and small droplets of water suspended in oil.
Approach: An integrated coupling of experiment and theory is involved in these investigations. The primary experimental tools are ultra-fast lasers that are used to probe the molecular characteristics of molecules at the top layer of the water surface. This is done with a nonlinear optical technique, vibrational sum frequency spectroscopy (VSFS), a powerful surface specific vibrational spectroscopic method for measuring the molecular structure of aqueous surfaces. Pendant drop tensiometry, infrared reflection-absorption spectroscopy, light scattering, and zeta potential measurements complement the VSF studies. Both classical and ab initio molecular dynamics calculations arembe used in conjunction with the experimental studies to derive information such as population densities, orientational distributions and the nature of bonding of different molecules across the interfacial region. This information is incorporated into calculations of VSF spectra to compare directly with experiment.
More information about the instrumentation and individual studies can be found on the Research Team Blog page.