Interfacial Phenomena Near Phase Transitions

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This project will investigate a variety of surface processes that occur when either a bulk or a surface phase transition takes place. One topic consists of a polarization atomic force microscopy and microscopic interferometry study of the shape and line tension of droplets on surfaces, from scales of nanometers through to many microns, in the vicinity of a wetting transition. These data should reveal the influence of surface interactions, surface heterogeneities, and temperature on such droplets. A second topic is an atomic force microscopy and spectroscopic ellipsometry study of critical finite-size effects within thin critical films to ascertain the critical fluctuation force and composition profile within such films. The final topic is an ellipsometry study of dipole-induced surface orientational order at the liquid-vapor surface of critical binary liquid mixtures to examine how dipole interactions influence the composition profile and orientational order at such interfaces. Line tension effects of droplets on surfaces and the universal aspects of surface critical phenomena, in both finite and semi-infinite systems, are poorly understood. Droplet line tensions strongly influence the nucleation and coalescence of droplets on surfaces, while, surface critical phenomena are particularly important in many supercritical extraction processes used in the food, pharmaceutical, and petroleum industries. An improved understanding of surface phenomena will lead to better control of surface related processes and ultimately to the ability to design surfaces possessing desirable characteristics on the molecular length scale. These projects will provide graduate students with excellent training using innovative surface techniques on topics at the forefronts of knowledge. This research will prepare these students well for academic, industrial, or government careers.%%%This work seeks a quantitative understanding of the physical origins of a number of liquid surface processes in the vicinity of either a surface or a bulk phase transition point where, respectively, either the surface or the bulk undergo a structural change as a function of temperature. Innovative optical and force microscopy techniques will be used to study the orientation of molecules at surfaces, the topography and associated energies of droplets on surfaces, and the structure of liquid mixtures within thin films. The data should reveal and how these phenomena are influence by surface interactions, surface heterogeneities, and bulk and surface phase transitions. An understanding of droplet topography and how it is influenced by surface interactions and the presence of a surface phase transition is important in governing (i) the uniformity of surface coatings used in many manufacturing processes and (ii) the wetting or non-wetting properties of fabrics and fibers. Similarly, surface phenomena in the vicinity of a bulk phase transition plays an extremely important role in many supercritical extraction processes used in the food, pharmaceutical, and petroleum industries. An improved understanding of these processes will lead to a better control of surface related processes and ultimately to the ability to design surfaces possessing desirable characteristics on the molecular length scale. Students involved in this research will gain a comprehensive training in physics and material science which will prepare them well for careers in the academic, industrial, or government arena.