In this award, funded by the Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division, Prof. Mark Ediger and Dr. Stephen Swallen of the University of Wisconsin - Madison and their graduate research students will explore the dynamics of supercooled liquid phases prepared via physical vapor deposition. The recent discovery of unusual molecular mobility within these phases has prompted many questions that reach to the heart of glassy material behavior. The research will involve a number of advanced tools, including secondary ion mass spectrometry (SIMS), probe molecule photobleaching and, in collaboration with Professor Ranko Richert of Arizona State University, dielectric spectroscopy measurements. The researchers will probe the nature of these unusually mobile liquids by observing the manner in which they transform into the ordinary liquid.
The glassy state of matter is ubiquitous in nature, and also has a number of useful technological applications, from the fabrication of better structural materials to the development of organic electronics and improved formulations for pharmaceuticals. Besides the broader technological impacts of the research being supported, Prof. Ediger and his student colleagues will continue their involvement in the University of Wisconsin - Madison's PEOPLE Program, providing educational enrichment in the summer for high school sophomores from groups under-represented in the sciences.
Most of us are familiar with the idea that a pure substance can exist as a vapor, liquid, or a solid, depending upon the temperature. Recently it has been proposed that a pure substance can possess two distinct liquid states. As far as is known, there is no fundamental law of that forbids this. There are a number of experiments that support the idea that at least some substances, including water, can have two distinct liquid states. This is an important idea, which in the case of water, could explain many of the unusual properties of liquid water. About five years ago, it was reported that physical vapor deposition might produce unusual liquids of two substances: trisnaphthylbenzene (TNB) and indomethacin (IMC). Physical vapor deposition is a method in which a solid is formed directly from the vapor; heating this solid produces a liquid. The major goal of this grant was to use several experimental techniques to investigate the liquids of TNB and IMC formed by this route, and to determine if they were distinct from the ordinary liquid formed by melting the crystal. A major result of this grant, supported by multiple independent experimental methods, is that the liquid formed by physical vapor deposition is the same as the liquid formed by melting the crystal. A second major result, achieved with the tools developed for this work, is that glasses of IMC with unprecedented temperature resistance can be prepared by vapor-depositing a capping layer of TNB on top of the vapor-deposited IMC. This builds upon recent work from our laboratory showing that vapor deposition conditions can be manipulated to significantly increase the stability of the resulting glassy solids. In the context of our work, a "glass" is any solid that does not exhibit the regular molecular packing of a crystal. This work may have a broad impact on technology and society in two respects. Although TNB and IMC are model glassformers, what is learned here will likely have an impact in organic electronics where the active materials are often glasses of a similar nature. If our capping strategy turns out to be general, which we think is likely to be true, this method could be used to produce glasses for organic electronics that are better than those currently utilized. Organic light emitting diodes (used in some cell phone displays) and organic photovoltaics are two examples of devices based upon organic electronics. In addition, this grant advanced the training of graduate, undergraduate, and high school students, through the integration of chemistry research and education activities. The principal investigator and his students worked with the University of Wisconsin-Madison’s PEOPLE program to prepare high school students from under-represented groups for college. Those supported by this grant refined a physical science curriculum for summer educational outreach. Each summer, they staffed a thirty-hour course for 15-20 high school juniors. The PEOPLE program has a proven track record of preparing students to succeed in college. Currently, the University of Wisconsin-Madison has more than 200 undergraduates who participated in the PEOPLE program as high school students.
