Fluctuations and Structure at Liquid-Liquid Interfaces

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Synchrotron x-ray surface scattering and Brewster angle microscopy will be used in a program of research and education to investigate fluctuations and structure at the liquid-liquid interface. Students will be trained to use cutting-edge synchrotron techniques to study interfacial phenomena. This research addresses the poorly understood area of molecular ordering and structure at liquid-liquid interfaces. This interdisciplinary area has important consequences for understanding inhomogenieties in condensed matter systems, and molecular organization at soft interfaces. The results will be relevant to a range of chemical and biological systems. The areas of study are: (1) Molecular ordering and phase transitions in surfactant monolayers at the water-oil interface, (2) Test of a recent hypothesis about the role of capillary waves and intrinsic structure in determining the interfacial width between water and alkanes, (3) Determination of the interfacial Hamiltonian through the study of fluctuating interfaces interacting over short distances in thin wetting films; and (4) Development of a new model system suited for structural studies of the adsorption of larger biomolecules to lipid membranes.Surfactant molecules preferentially adsorb to the interface between two liquids, such as oil and water. The surfactants act as a bridge that connects two types of materials that would, otherwise, not mix. These surfactants play an important role in many domestic products, such as shampoos, paints, and plastics. More importantly, surfactants form the basis for biological cell membranes that support the formation of life on earth. From the point of view of condensed matter physics, it is important to understand how large numbers of molecules arrange themselves at interfaces because the makeup of these interfaces determine many important properties of materials. Chemists and biologists are also interested in the way molecules arrange themselves and transport through liquid interfaces. This is important, for example, in the separation of toxic from non-toxic chemicals and in controlling which biological molecules can enter different parts of cells or the liquid region between cells. Due to the importance of these systems they have been studied for many years. However, an understanding of the structure on the molecular length scale is lacking. During the past three years, NSF support has enabled the development of powerful x-ray scattering techniques that directly probe the organization of molecules at the liquid-liquid interface. The present grant supports the training of students in the further development and application of these techniques to areas of physical, chemical, and biophysical interest.