With support from the Solid State and Materials Chemistry program, Lian Yu and his student coworkers at the University of Wisconsin - Madison will study Surface Crystallization and Diffusion of Organic Glasses (DMR 1206724). Glasses constitute an important class of solids produced by cooling liquids, condensing vapors, and evaporating solutions while avoiding crystallization. According to the current view that crystallization is controlled by diffusion, glasses should not crystallize readily. Yet many do crystallize, sometimes surprisingly fast. Recent work has discovered new modes of crystal growth that emerge as organic liquids are cooled to become glasses. This study seeks to understand one such process: fast crystal growth at the surface of organic glasses. The team will test the hypothesis that the phenomenon arises because of surface molecular mobility and the possibility for surface crystals to grow toward free space. They will determine how molecules are transported to support upward-lateral growth of surface crystals through real-time high-resolution microscopy. Surface diffusion coefficients will be measured for organic glasses to learn whether surface diffusion can sustain surface crystal growth. Experiments will be performed to determine the effect of glass aging on surface crystallization and diffusion, and how the fast growth of surface crystals is terminated as glasses are heated to become liquids. Polymer additives will be used to perturb crystallization and diffusion to understand their role in stabilizing organic glasses against crystallization. The team will study how the nature of surface mobility changes from hard inorganic solids to soft organic solids, from crystals to glasses, and from small-molecule glasses to polymer glasses.
NON-TECHNICAL SUMMARY: The results of this research will benefit many areas of science and technology in which crystallization, glasses, and surfaces are important. Glasses are amorphous materials that combine solid-like mechanical stability and liquid-like spatial uniformity, making them ideal for many applications ranging from telecommunication to bio-preservation. Understanding glass crystallization will benefit the fabrication of glass ceramics and control of bio-mineralization, for which amorphous solids are key precursors. This research will improve the stability of organic glasses against crystallization and advance their applications in electronic and biomedical technologies. Pharmaceutical scientists will benefit from this knowledge as they develop amorphous formulations to deliver poorly soluble drugs. Poor solubility is limiting the development of many drugs that are beneficial and can significantly advance health care in the U.S. and developing countries. This project will provide rates of surface diffusion on organic materials, which are essential for understanding and controlling many technological processes - crystal growth, sintering, stability of thin films, and durability of nano-materials. Although extensive data exist for metals and semiconductors, the data are lacking for soft organic materials. Graduate and undergraduate students will benefit from the multi-disciplinary nature of this project, having significant exposure to crystals and glasses, high and low molecular weight organic materials, and both industrial and academic research labs. Personnel supported by this grant will work with UW-Madison's Pre-college Enrichment Opportunity Program for Learning Excellence (PEOPLE), which has a proven record of increasing the enrollment of minority and low-income high school students to colleges and universities. This program provides experiences that help students to become scientifically literate citizens and encourages them to consider careers in science and engineering.
