Investigation of Vapor-deposited Glasses by Nanocalorimetry Dielectric Relaxati

Overview: Experiments are proposed to investigate vapor-deposited glasses of simple organic molecules using in situ nanocalorimetry and dielectric relaxation. Molecules to be studied include decahydroisoquinoline, 2-methyltetrahydrofuran, 2-picoline, m-cresol, t-butanol, and propylene carbonate. The first objective of this work is to study the extent to which secondary relaxation processes in vapor-deposited glasses are suppressed relative to liquid-cooled glasses. A second objective is to test whether deposition in the presence of a large electric field can produce glasses with even higher kinetic stability. The third objective is to understand why some organic molecules do not form highly stable glasses when vapor-deposited. Intellectual merit: The potential energy landscape provides a useful framework for discussing the thermodynamic and dynamic properties of liquids and glasses. Recent work has established that vapor-deposited glasses can exhibit extraordinary kinetic stability and also have other properties expected only for glasses prepared by slow cooling from the liquid over the timescale of thousands of years or more. Thus vapor-deposited glasses provide a unique opportunity to understand the properties of amorphous states deep in the potential energy landscape. The nature of these low energy states holds the key to understanding the ultimate properties of amorphous solids and the ultimate fate of liquids upon slow cooling. Initial experiments show that secondary relaxations can be suppressed by more than a factor of three in vapor-deposited glasses, indicating that these glasses are closely approaching an ideal glass state. The proposed experiments will explore suppression of several different types of secondary relaxation processes and also provide information about characteristic barrier heights within the metabasins present deep in the energy landscape. Deposition in the presence of a large electric field may allow a test of the role of entropy in determining the heights of barriers between metabasins deep in the landscape. By studying a wide range of small organic molecules, an understanding of the molecular features needed for stable glass formation will emerge. Experiments over a range of deposition rates will test whether failure to form a stable glass is a consequence of kinetics or thermodynamics. Broader impacts: The proposed work will have a broad impact in two respects. Glasses play an important role in modern technology: optical fibers are critical for modern communications, metallic glasses are used in the highest efficiency electrical transformers, polymer glasses form the structure of new commercial aircraft, and organic glasses are the active layers in some light emitting diodes (OLEDs). The proposed experiments on model supercooled liquids and glasses will provide increased fundamental understanding and it is expected that this will enable the production of improved glasses that are useful in applications. For example, if we understand more about the mechanisms by which vapor-deposited glasses are formed, it may be possible to produce glasses for OLEDs that lead to improved efficiency and long-term stability. In addition, the funding of this proposal will also advance the training of graduate, undergraduate, and high school students, through the integration of chemistry research and education activities. The PI and his students will help prepare high school students from under-represented groups for college by working with the University of Wisconsin-Madisons PEOPLE program. Those supported by this grant will refine a materials chemistry curriculum for summer educational outreach and each summer present a thirty-hour course for 15 high school juniors. The PEOPLE program has a proven track record of preparing students to succeed in college.