Many phenomena occur primarily or exclusively at interfaces. These include adhesion, friction, lubrication, chromatographic separations, catalysis and many biological processes. The goal of our research is to establish links between molecular structure and function in interfacial systems. To accomplish this, we use a non-linear spectroscopy technique known as vibrationally resonant sum-frequency generation (VR-SFG). This technique allows us to probe molecules at interfaces without interfering signal from molecules in the bulk. It also allows us to determine the orientation of molecules at these interfaces. We are currently studying two types of systems: solid-solid interfaces relevant to adhesion and solid-liquid interfaces relevant to chromatography.

The goal of our first project is to better understand the molecular basis of adhesion or, in less technical terms, what makes things stick. We are using VR-SFG to determine the molecular structure of polymer surfaces and the interface between two polymeric materials. We will also correlate the results of the spectroscopy measurements with mechanical strength tests. This will allow us to better identify the molecular structures that give strong adhesive bonds. Our findings will pave the way for the development of new adhesives designed from molecular considerations. This work is currently being funded by the Air Force Office of Scientific Research.

In our second project, we are looking at the molecular basis for chromatographic separations. High performance liquid chromatography (HPLC) is used in many analytical and biomedical fields to separate chemical species, but a molecular level understanding of the fundamental processes is lacking. We are currently studying model HPLC stationary phases under high pressure. Our results show that the structure of the interface changes both with pressure and how the samples are stored. We will soon be changing the composition of the liquid phase to learn more about how those conditions influence retention in HPLC. Our results will lead to improved predictions of optimal separation programs which will in turn improve the efficiency of HPLC analysis.

Students in our research group use a state-of-the-art, ultra-fast laser system to perform the non-linear spectroscopy measurements. They also prepare and characterize our samples, using such techniques as polymer spin coating, ellipsometry (in the lab of Prof. Linford), and silane chemistry. Most importantly, we study interesting systems that impact many fields of science and engineering.