Imaging the Dynamics of Freezing and Melting with Colloids

*非技术摘要*晶体的冻结和熔化是令人着迷的重要技术现象，但在实验室中很难研究。在单个原子形成晶体时跟踪它们的运动的实验可以提供强大的洞察力，但重大的技术挑战阻碍了许多必要的测量。该项目将使用悬浮在溶液中的微观球形颗粒(胶体颗粒)作为模型原子。用来研究结晶和熔化。这些粒子遵循支配原子或分子的相同物理原理，但比原子大得多，速度也慢得多，因此在光学显微镜下直接可见。这些实验将为瞬变结构的作用提供新的见解。瞬变结构不稳定，但仍然可以控制晶体生长或熔化的速度，甚至阻止晶体生长。这项研究可能导致蛋白质更有效的结晶(确定其结构和功能的主要步骤)，以及纳米粒子中原子的受控结晶(可能导致新材料)。该项目将为研究生和本科生提供培训，并包括向高中生伸出援手，让他们接触尖端科学领域的兴奋和职业机会。该项目还将支持从事工业研究的物理学家进行一系列新的访问和研讨会，目的是为合作研究创造机会，并让学生有一系列的职业选择。*技术摘要*冻结和融化现象在日常生活中很常见，多年来一直被深入研究，但许多重要问题仍未得到解答。最近的实验表明，微米级的粒子或液滴可以作为强大的实验模型，以单粒子分辨率提供对这些现象的直接洞察。这一个人研究人员奖支持使用胶体球体和液滴的实验，这些胶体球体和液滴的相互作用势可以调节以诱导结晶、凝胶化或熔化。使用光学显微镜将在二维或三维上定量跟踪粒子的运动。特别令人感兴趣的是热力学亚稳态的作用，它对自由能垒、速率和系统陷入不平衡情况下的最终状态有重大影响。这些结果将有助于球状蛋白质的结晶或无机纳米晶的合成。研究生和本科生将在该项目中发挥关键作用，并接受实验室研究方面的培训。一项外展计划将让高中生接触尖端科学的兴奋和职业潜力。反映了研究人员？S结合了软物质的工业应用和研究生培训的兴趣，该项目还将支持目前在工业领域工作的物理学家的一系列访问和研讨会。

****NON-TECHNICAL ABSTRACT****The freezing and melting of crystals are fascinating and technologically important phenomena, yet are very difficult to study in the laboratory. Experiments that follow the motions of individual atoms as they form crystals can provide powerful insight, but major technical challenges prevent many of the needed measurements. This project will use microscopic spherical particles suspended in solution (colloidal particles) as ?model atoms,? with which to study crystallization and melting. These particles follow the same physical principles that govern atoms or molecules, but are much larger and slower than atoms and hence directly visible in optical microscopes. The experiments will offer new insight into the role of transient structures, which are not stable but which can nonetheless control the rate at which crystals grow or melt, or even arrest crystal growth. The research may lead to more efficient crystallization of proteins (a major step in determining their structure and function), and controlled crystallization of atoms in nanoparticles (potentially leading to novel materials). The project will provide training for graduate and undergraduate students and includes outreach to high-school students to expose them to the excitement and career opportunities in cutting-edge science. The project will also support a new series of visits and seminars by physicists working in industrial research, with the goals of creating opportunities for collaborative research and of exposing students to a range of career options.****TECHNICAL ABSTRACT****The phenomena of freezing and melting are familiar in everyday life and have been studied intensively for many years, but many important questions remain unanswered. Recent experiments have shown that micron-sized particles or droplets can be used as powerful experimental models, providing direct insight into these phenomena with single-particle resolution. This individual-investigator award supports experiments with colloidal spheres and liquid droplets whose interaction potentials can be tuned to induce crystallization, gelation, or melting. The particle motions will be quantitatively tracked in two or three dimensions using optical microscopy. Of particular interest is the role of thermodynamically metastable states, which have a major effect on the free-energy barriers, the rates, and on the final state in cases where the system is trapped out of equilibrium. The results should be helpful in applications such as crystallization of globular proteins or synthesis of inorganic nanocrystals. Graduate and undergraduate students will play key roles in the project and receive training in laboratory research. An outreach program will expose high-school students to the excitement and career potential of cutting-edge science. Reflecting the investigator?s combined interests in industrial applications of soft matter and in training graduate students, the project will also support a series of visits and seminars by physicists currently working in industry.