Surface Crystallization and Diffusion of Organic Glasses

技术概述：在固态和材料化学项目的支持下，李宇和他在威斯康星大学麦迪逊分校的学生同事将研究有机玻璃的表面结晶和扩散（DMR 1206724）。玻璃是一类重要的固体，由冷却液体、冷凝蒸汽和蒸发溶液而避免结晶而产生。根据目前的观点，结晶是由扩散控制的，玻璃不应该容易结晶。然而，许多确实会结晶，有时速度惊人。最近的研究发现了晶体生长的新模式，当有机液体被冷却成玻璃时，就会出现这种新模式。这项研究试图了解这样一个过程：在有机玻璃表面的快速晶体生长。该团队将测试一种假设，即这种现象是由于表面分子的流动性和表面晶体向自由空间生长的可能性而产生的。他们将通过实时高分辨率显微镜确定分子如何运输以支持表面晶体的向上横向生长。将测量有机玻璃的表面扩散系数，以了解表面扩散是否能维持表面晶体生长。实验将确定玻璃老化对表面结晶和扩散的影响，以及当玻璃被加热成液体时，如何终止表面晶体的快速生长。聚合物添加剂将用于干扰结晶和扩散，以了解它们在稳定有机玻璃不结晶中的作用。该团队将研究表面迁移率的性质如何从坚硬的无机固体到柔软的有机固体，从晶体到玻璃，从小分子玻璃到聚合物玻璃。非技术总结：这项研究的结果将有利于许多科学和技术领域，其中结晶，玻璃和表面是重要的。玻璃是一种无定形材料，结合了固体状的机械稳定性和液体状的空间均匀性，使其成为从电信到生物保存等许多应用的理想选择。了解玻璃结晶将有助于玻璃陶瓷的制备和生物矿化的控制，其中非晶固体是关键的前体。该研究将提高有机玻璃的抗结晶稳定性，促进其在电子和生物医学技术中的应用。制药科学家将从这些知识中受益，因为他们开发出非晶配方，以提供难溶性药物。在美国和发展中国家，低溶解度限制了许多有益的药物的开发，这些药物可以显著地促进医疗保健。该项目将提供有机材料的表面扩散速率，这对于理解和控制许多技术过程至关重要-晶体生长，烧结，薄膜稳定性和纳米材料的耐久性。虽然在金属和半导体方面有大量的数据，但在软质有机材料方面却缺乏数据。研究生和本科生将受益于这个项目的多学科性质，有大量的接触晶体和玻璃，高分子量和低分子量有机材料，以及工业和学术研究实验室。这项拨款支持的人员将与威斯康辛大学麦迪逊分校的大学前学习卓越丰富机会计划（PEOPLE）合作，该计划在增加少数民族和低收入高中学生进入学院和大学方面有着良好的记录。这个项目提供了帮助学生成为具有科学素养的公民的经验，并鼓励他们考虑从事科学和工程方面的职业。

TECHNICAL SUMMARY: 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.