Liquid surfaces and interfaces play crucial roles in physics, chemistry, geology, biology, etc., and in a large variety of real-world processes and products such as lubrication, adhesion, filtration, oil recovery, wetting/spreading/coating, aerosols and emulsions, etc. It has long been theoretically predicted that all liquids will have non-isotropic order (layers) near their free surfaces, in contrast to the conventional view of the liquid state as an isotropic continuum. In recent years, as a result of NSF-supported research in this group, it has been established that nonmetallic liquids do develop surface order at sufficiently low temperatures. The structural and mechanical properties of these surfaces will be characterized in detail using X-ray reflectivity, off-specular scattering, and X-ray photon correlation spectroscopy. Relationships will be sought between the ordering of these liquids at their free surfaces and their ordering at liquid-solid interfaces, to try to learn whether these can be explained within a common framework. Identification of universal qualitative and quantitative features and trends will be sought in order to help the development of a more advanced theoretical picture. This project will integrate research and teaching by training graduate students in an interdisciplinary environment. Liquids-related topics will be incorporated into undergraduate and graduate courses and web-disseminated teaching materials. The results of the research will be made available through traditional scientific channels and also through web pages.
Liquid surfaces and interfaces play crucial roles in physics, chemistry, geology, biology, etc., and in a large variety of real-world processes and products such as lubrication, adhesion, filtration, oil recovery, wetting/spreading/coating, aerosols and emulsions, etc. As a result of recent advances, it is now known that the atoms or molecules in liquids can arrange themselves into layers near the surface. The nanoscale surface region thus resembles a liquid crystal rather than the liquid itself. The objective of this project is a detailed and systematic study of this phenomenon using synchrotron radiation. The knowledge gained from these studies may help determine not only how liquid surface properties are different from bulk liquid properties, but why. Therefore, these studies may ultimately lead to benefits to society from being able to better control processes occurring at surfaces. This project will integrate research and teaching by training graduate students in an interdisciplinary environment. Liquids-related topics will be incorporated into undergraduate and graduate courses and web-disseminated teaching materials. The results of the research will be made available through traditional scientific channels and also through web pages.
Many scientists think of liquids as continuous (uniform) materials, but liquids are made up of individual molecules that are not always arranged randomly. This is especially true at surfaces and interfaces. Since the arrangements of molecules determines the properties of a material, studies of ordering phenomena in liquids give insight into physical, chemical, biological and mechanical processes that can occur at liquid surfaces and liquid-solid interfaces. Research supported by this project has yielded a number of exciting results, including the following: (a) We have proved experimentally that when water is in apparent contact with a hydrophobic surface (for example, beads of water on a waxed car), there is a nanoscale gap between the water and the surface. The bead does not actually touch the waxed surface, but floats slightly above it. This explains why such beads slide so easily over the waxed surface, and studies such as these may provide information helpful in the development of energy-efficient low-friction pipelines, or easy manipulation of small droplets in "labs-on-a-chip", etc. (b) Living organisms grow inorganic crystals, such as those that make up bones and shells, by using organic molecules to "tell" the crystals how and where to grow. Mimicking aspects of this biological process, we showed that oriented gold nanocrystals can be grown by making a solution of gold chloride and putting it in contact with a suitable organic surface that acts as a template. The gold crystals are nucleated by the template and grow in a precisely tailored fashion. Not only is this a new way of making gold nanoparticles, but more generally it suggests the possibility of making designed crystals of various kinds with the help of ideas derived from biology.
