In this collaborative project, Profs. Lian Yu, Mark Ediger, and Juan de Pablo of the University of Wisconsin ? Madison, Dr. Geoff Zhang of Abbott Laboratories, and their research student colleagues will investigate the crystallization of organic glasses. Glasses are liquids that are too cold to flow. According to the current view that crystallization is controlled by diffusion, organic glasses should not crystallize readily. Yet recent work has shown that many do crystallize, sometimes at rates 105 times faster than predicted by the standard models. This study concerns two modes of crystal growth activated near the glass transition temperature: a bulk mode and a surface mode. Both growth modes are too fast to be controlled by bulk diffusion. The team will test the hypothesis that molecular motions native to the glassy state can cause crystal growth, without involving substantial bulk diffusion, if sufficient similarity exists between the crystal and liquid structures. They will determine whether crystal growth in the glassy state becomes faster if bulk molecular motions are amplified with an external field. They will study whether surface-enhanced crystal growth results from surface-enhanced molecular mobility. Surface diffusion coefficients of organic glasses will be measured for the first time by the method of surface grating decay and correlated with surface crystal growth rates. The project will examine what properties of coating materials are important for suppressing surface crystallization. Computer simulations will identify the underlying mechanisms of bulk and surface crystal growth of organic glasses. For each growth mode, a screening experiment will be performed to assess its generality and polymer additives will be added to perturb it for further insights on its mechanism and control. NON-TECHNICAL SUMMARY: Crystallization influences almost every aspect of modern technology. While it has been extensively studied for hard inorganic materials, crystallization remains poorly understood for organic materials. In this collaborative project, a team of academic and industrial researchers will seek to understand the crystallization of organic glasses. Glasses are liquids that are too cold to flow; they are the preferred materials for many applications, ranging from pharmaceutical development to telecommunication. The team will study the activation of new, fast modes of crystal growth as a liquid becomes a glass and the control of these new modes in developing amorphous materials. The results of this research will benefit scientists in a range of fields where crystal growth is important; for example, amorphous pharmaceuticals and organic electronics. The enormous potential of using amorphous solids to enhance the bioavailability of poorly soluble drugs has motivated Abbott to partner with the University of Wisconsin in this project. It is a unique advantage that the Chicago-based Abbott is only a short distance away from Madison, enabling close interactions between the collaborators. Graduate and undergraduate students will benefit from the multi-disciplinary nature of this project, having significant exposure to experiments and simulations, 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 in 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.
In this collaborative project, Profs. Lian Yu, Mark Ediger, and Juan de Pablo of the University of Wisconsin – Madison, Dr. Geoff Zhang of Abbott Laboratories, and their research student colleagues investigated the crystallization of organic glasses. Glasses are liquids that are too cold to flow. According to the current view that crystallization is controlled by diffusion, organic glasses should not crystallize readily. Yet recent work has shown that many do crystallize, sometimes at rates 105 times faster than predicted by the standard models. The team studied two modes of crystal growth activated near the glass transition temperature: a bulk mode and a surface mode. Both growth modes are too fast to be controlled by bulk diffusion. The team established that molecular motions native to the glassy state can enable crystal growth, without involving substantial bulk diffusion, if sufficient similarity exists between the crystal and liquid structures. Their study showed that surface-enhanced crystal growth results from surface-enhanced molecular mobility and freedom for surface crystals to grow upward, but not the easier release of crystallization-induced tension. Surface diffusion of organic glasses was measured for the first time by the method of surface grating decay and shown to be able to support fast surface crystal growth. Computer simulations were performed to identify the underlying mechanisms of bulk and surface crystal growth of organic glasses. Polymer additives were added to perturb crystal growth in organic glasses for further insights on its mechanism and control. The research findings have been presented in 18 papers in high-impact journals of basic and applied science. Crystallization influences almost every aspect of modern technology. While it has been extensively studied for hard inorganic materials, crystallization remains poorly understood for organic materials. In this collaborative project, a team of academic and industrial researchers advanced the understanding of the crystallization of organic glasses. Glasses are liquids that are too cold to flow; they are the preferred materials for many applications, ranging from pharmaceutical development to telecommunication. The team studied the activation of new, fast modes of crystal growth as a liquid becomes a glass and the control of these new modes in developing amorphous materials. The results of this research will benefit scientists in a range of fields where crystal growth is important; for example, amorphous pharmaceuticals and organic electronics. The enormous potential of using amorphous solids to enhance the bioavailability of poorly soluble drugs has motivated Abbott to partner with the University of Wisconsin in this project. This multi-disciplinary project involved experiments and simulations, crystals and glasses, high and low molecular weight materials, and industrial and academic research labs; it has provided training for 9 graduate students, 7 postdoctoral researchers, and 5 undergraduates. Three graduate students received their Ph.D.’s on the basis of their work on this project, and are now pursuing scientific research in academia and industry. Three postdoctoral researchers are now faculty members. Personnel supported by this grant worked with University of Wisconsin’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 in colleges and universities. The research findings have been incorporated into the course materials for Molecular Solids, a graduate course taught by Lian Yu to students from Pharmaceutical Sciences, Chemistry, Chemical Engineering, and Food Science, and from industrial companies, and into short courses to industrial scientists organized by University of Wisconsin Extension Service and the Association of American Pharmaceutical Scientists. It is significant that this NSF-supported project has been augmented by additional industrial funding to develop the technology of stable amorphous pharmaceuticals for delivering poorly soluble drugs.
